Teach Yourself PHP 4 in 24 hours

sams teach yourself php4 in 24 hours - Upload a Document to Scribd

No tf or co m er cia l, us e fo re du ca http://i-tronics.blogspot.com/ tio n 1 on ly 3 originally graduated in philosophy and has learned his trade by reinventing wheels and then working out why they don't run straight. Matt has taught courses in HTML, JavaScript, Perl, and PHP and was a contributing author to Dynamic HTML Unleashed. When not coding, Matt is a committed urban cyclist, a Guinness drinker, an obsessive reader, and a writer of unpublishable short stories. One day he claims he will write a novel. No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 4 Acknowledgments The open source concept made both my career and this book possible. I would like to thank all those people whose voluntary efforts continue to defy the received wisdom. Particular thanks to the PHP community, especially contributors to the PHP mailing lists whose postings revealed pitfalls, suggested techniques, and kept me amused. From Macmillan, I would like to thank Randi Roger for suggesting me for this project as well as Jeff Schultz, Paul Schneider, and Scott Meyers for support and tolerance as deadlines loomed and panic set in. extreme vagueness on any matter not pertaining to PHP. In particular, my business partner circumstances, and Dave Urmson, who took over formatting when the going got tough. Other Corrosive stars include Anisa Swaffield, Jeff Coburn, Mai Chokelumlerd, and Moira Govern. I must also thank Small Planet (http://www.smallpla.net) for providing me with additional development space and allowing me to use it to play with beta software. Particular thanks to Mohammed Abba and Clive Hills, who recompiled PHP on the Small Planet system more times than we care to remember. graciously agreed to act as guinea pigs. One of the best ways to test a tutorial text is to use it in class. Thanks to my PHP students who Thanks also to my partner Louise and our new daughter Holly for being there, and bearing the As my social life took second place to PHP, my local became a refuge for last minute pint and proofing sessions. Thanks to Alan and Dora of the Prince Arthur for running the perfect pub. Tell Us What You Think! As the reader of this book, you are our most important critic and commentator. We value your opinion and want to know what we're doing right, what we could do better, what areas you'd like to see us publish in, and any other words of wisdom you're willing to pass our way. You can fax, email, or write me directly to let me know what you did or didn't like about this book— as well as what we can do to make our books stronger. No Please note that I cannot help you with technical problems related to the topic of this book, and that due to the high volume of mail I receive, I might not be able to reply to every message. When you write, please be sure to include this book's title and author as well as your name and phone or fax number. I will carefully review your comments and share them with the author and editors who worked on the book. Fax: 317-581-4770 tf or co m er Finally, thanks to the fishes, who cheered up a lurker. cia l, grumpy, hunched, and obsessed character I became while writing this book. http://i-tronics.blogspot.com/ us e fo re du ca Massimo Guglielmino, who kept the Corrosive show on the road under the usual stressful tio n Thanks must also go to all at Corrosive for putting up with my continued absence and my on ly 5 Email: Mail: Mark Taber Associate Publisher Sams Publishing 201 West 103rd Street Indianapolis, IN 46290 USA No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 6 Introduction This is a book about PHP, the open source Web scripting language that has joined Perl, ASP, and Java on the select list of languages that can be used to create dynamic online environments. It is also a book about programming. In the space available, it is neither technique that PHP offers. Nevertheless, whether you are an experienced programmer enough information to get your journey off to a good start. possible to create a complete guide to programming in PHP nor to cover every function and considering a move to PHP or a newcomer to scripting, the steps in this book should provide Who Should Read This Book? This book will take you from the first principles through to a good working knowledge of the PHP4 programming language. No prior experience of programming is assumed, though if you have worked with a language such as C or Perl in the past, you will find the going much easier. PHP4 is a Web programming language. To get the most from this book, you should have some understanding of the World Wide Web and of HTML in particular. If you are just starting out, you are comfortable creating basic documents and can build a basic HTML table, you will be fine. you will still be able to use this book, though you should consider acquiring an HTML tutorial. If written to work with MySQL, a SQL database that is free for personal use on some platforms. We include a short introduction to SQL, but if you intend to use PHP to work with databases, you might want to spend some time reading up on the subject. Numerous introductory SQL tutorials are available online. If you intend to work with a database other than MySQL, many of functions designed to query your database. the examples in this book will be relatively easy to reproduce with the equivalent PHP No How This Book Is Organized This book is divided into four parts: Part 1 is an introduction to PHP4. Part 2 covers the basic features of the language. Pay particular attention to this section if you are new to programming. tf or co m er cia l, PHP4 is designed to integrate well with databases. Some of the examples in this book are http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 7 Part 3 covers PHP4 in more detail, looking at the functions and techniques you will need to become a proficient PHP programmer. Part 4 illustrates a complete self-contained example. Part 1 contains Hours 1 through 3 and handles the information you will need to get your first script up and running: and looks at some of the compelling reasons for deciding to learn this scripting language. Hour 1, "PHP: From Home Page to Portal," describes the history and capabilities of PHP Hour 2, "Installing PHP," explains how to install PHP on a UNIX system and discusses hour, we also look at PHP configuration options. Hour 3, "A First Script," looks at the different ways in which you can embed a PHP script in a document and create a script that writes text to the user's browser. Part 2 comprises Hours 4 through 8. In this part, you will learn the basic components of the PHP language: data types, operators, and expressions. Hour 4, "The Building Blocks," covers the basics of PHP. You will learn about variables, Hour 5, "Going with the Flow," covers the syntax for controlling program flow in your scripts. Hour 6, "Functions," explores the use of functions to organize your code. We will also look at some of the functions that PHP4 provides to manipulate arrays. Hour 8, "Objects," introduces PHP4's support for classes and objects. Throughout the course of the hour, we will develop a working example. Part 3 consists of Hours 9 through 22. In this part, you will come to grips with the features and techniques of the language: Hour 9, "Working with Forms," introduces the dimension of user input through the Hour 10, "Working with Files," shows you how to work with files and directories on the local machine. Hour 11, "Working with the DBM Functions," demonstrates PHP4's support for DBM Hour 12, "Database Integration— MySQL," provides a brief introduction to SQL syntax and introduces the PHP4 functions that can be used to work with the MySQL database. Hour 13, "Beyond the Box," covers some of the details of HTTP requests and looks at PHP network functions. No tf database systems, versions of which are available on most systems. or mechanism of the HTML form. You will learn how to gather data submitted via a form. co m er cia l, Hour 7, "Arrays," discusses the array data type that can be used to hold list information. http://i-tronics.blogspot.com/ us statements. e In addition to if and switch constructs, you will learn about loops using for and while fo re du ca tio n some of the configuration options you might want to choose when compiling PHP. In this on ly 8 Hour 14, "Working with Dynamic Images" explores PHP's image functions. With these, you can create GIF or PNG files dynamically. Hour 15, "Working with Dates," covers the functions and techniques you can use for date arithmetic. We create a calendar example. Hour 16, "Working with Data," revisits data types and explores some more of the functions you can use to work with data in your scripts. More array functions are also covered. Hour 17, "Working with Strings," covers the functions that you can use to manipulate strings. You can use these to find and replace complex patterns in strings. passing information across scripts and requests. 19, using PHP4's built-in session functions. Hour 18, "Working with Regular Expressions," introduces regular expression functions. Hour 19, "Saving State with Cookies and Query Strings," shows you some techniques for Hour 20, "Saving State with Session Functions," extends the techniques explored in Hour Hour 21, "Working with the Server Environment," shows you how to call external programs from your scripts and incorporate their output into your own. Hour 22, "Debugging," shows you some techniques that you can use to track down problems in your code. We also examine some common errors. some of the techniques that were introduced earlier in the book. Hour 23, "An Example (Part 1)," creates a brief for a club listings script. We build the code that will allow users to create accounts and enter listings. Hour 24, "An Example (Part 2)," concludes the project, building the code for nonmembers to browse the listings and look at club profiles. No tf or co m er cia l, http://i-tronics.blogspot.com/ us Part 4 consists of Hours 23 and 24. In these, we build a working example that incorporates e fo re du ca tio n on ly 9 co Overview tf 29 Platforms, Servers, Databases, and PHP Where to Find PHP and More 30 Installing PHP4 for Linux and Apache 30 32 --enable-track-vars 32 --with-gd 32 --with-mysql 33 m er Hour 1: PHP: From Home Page to Portal Overview 22 What Is PHP? 22 How Did PHP Evolve? 23 What's New in PHP4 24 The Zend Engine 24 Why Choose PHP? 25 Speed of Development 25 PHP Is Open Source 26 Performance 26 Portability 26 Summary 27 Q&A 27 Workshop 27 Quiz 27 Activity 28 Hour 2: Installing PHP 29 cia l, us e No or Some configure Options Configuring Apache 33 php.ini 34 short_open_tag 35 Error Reporting Directives 35 http://i-tronics.blogspot.com/ fo re du ca 29 tio 22 n SAMS Teach Yourself PHP4 in 24 Hours Acknowledgments 4 Tell Us What You Think! 4 Introduction 6 Who Should Read This Book? 6 How This Book Is Organized 6 2 on ly 10 m er Hour 4: The Building Blocks49 Overview 49 Variables 49 Dynamic Variables 50 References to Variables 52 Data Types 53 Changing Type with settype() Changing Type by Casting 57 cia l, us e Hour 3: A First Script 40 Overview 40 Our First Script 40 Beginning and Ending a Block of PHP Statements The print() Function 44 Combining HTML and PHP 44 Adding Comments to PHP Code 46 Summary 47 Q&A 47 Workshop 47 Quiz 48 Activity 48 or Operators and Expressions 58 The Assignment Operator Arithmetic Operators 59 co No tf The Concatenation Operator More Assignment Operators60 Comparison Operators 61 Creating More Complex Test Expressions with the Logical Operators 62 Automatically Incrementing and Decrementing an Integer Variable 63 Operator Precedence 65 http://i-tronics.blogspot.com/ fo re du ca 55 59 60 tio n 42 on ly Variable Directives 36 Help! 36 Summary 38 Q&A 38 Workshop 38 Quiz 38 Activity 39 11 What Is a Function? Calling Functions 88 Defining a Function 90 m er Constants 66 Predefined Constants 67 Summary 67 Q&A 67 Workshop 68 Quiz 68 Activities 69 Hour 5: Going with the Flow 70 Overview 70 Switching Flow 70 The if Statement 70 Using the else Clause with the if Statement 72 Using the elseif Clause with the if Statement 73 The switch Statement 75 Using the ? Operator 77 Loops 78 The while Statement 78 The do..while Statement 79 The for Statement 80 Breaking Out of Loops with the break Statement 82 Skipping an Iteration with the continue Statement 84 Nesting Loops 85 Summary 86 Q&A 86 Hour 6: Functions 88 Overview 88 No tf or Returning Values from User-Defined Functions 92 Dynamic Function Calls 93 Variable Scope 94 Accessing Variables with the global Statement 95 Saving State Between Function Calls with the static Statement 98 More About Arguments 100 Setting Default Values for Arguments 100 Passing References to Variables to Functions co cia l, us 88 e http://i-tronics.blogspot.com/ fo re du ca tio 102 n on ly 12 Summary 105 Q&A 105 Workshop 105 Quiz 106 Activity 107 Hour 7: Arrays 108 Overview 108 What Is an Array? 108 Creating Arrays 109 Defining Arrays with the array() Function 109 Defining or Adding to Arrays with the Array Identifier 110 Associative Arrays 110 Defining Associative Arrays with the array() Function 111 Directly Defining or Adding to an Associative Array 111 Multidimensional Arrays 112 Accessing Arrays 113 Getting the Size of an Array 113 Looping Through an Array 114 Looping Through an Associative Array 115 Outputting a Multidimensional Array 116 Manipulating Arrays118 Joining Two Arrays with array_merge() 119 Adding Multiple Variables to an Array with array_push() 119 No Sorting Numerically Indexed Arrays with sort() 122 Sorting an Associative Array by Value with asort() 123 Sorting an Associative Array by Key with ksort() 123 Summary 124 124 Workshop 125 Quiz 125 Activities 125 Hour 8: Objects126 Overview 126 tf or Q&A co Slicing Arrays with array_slice() Sorting Arrays 122 m er Removing the First Element of an Array with array_shift() 120 121 cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 13 Quiz 152 Activities 153 Hour 9: Working with Forms co m er What Is an Object? 126 Creating an Object 127 Object Properties 128 Object Methods 129 An Example132 Defining the Class's Properties 133 Creating a Constructor 133 The addRow() Method 134 The addRowAssocArray() Method 134 The output() Method 135 Bringing It All Together 136 What's Missing?139 Why a Class? 139 Inheritance 140 Overriding the Method of a Parent Class 141 Calling an Overridden Method 143 Inheritance: An Example 144 Defining HTMLTable's Properties144 Creating the Constructor 145 The setCellpadding() Method 146 The Output() Method 146 The Table and HTMLTable Classes in Their Entirety 147 Why Use Inheritance? 150 Summary 151 Q&A 152 Workshop 152 No tf or Overview 154 Global and Environment Variables 154 A Script to Acquire User Input 156 Accessing Input from Multiple SELECT Elements cia l, us e 154 Accessing All the Fields from a Form in an Associative Array 159 Distinguishing Between GET and POST Transactions 161 Combining HTML and PHP Code on a Single Page 162 Using Hidden Fields to Save State 165 http://i-tronics.blogspot.com/ fo re du ca tio 157 n on ly 14 Hour 10: Working with Files Overview 175 175 Working with Directories No Quiz 194 Activities 195 Hour 11: Working with the DBM Functions 196 tf or Reading the Contents of a Directory with readdir() 192 Summary 194 Q&A 194 Workshop 194 co 191 Creating Directories with mkdir() 191 Removing a Directory with rmdir() 192 Opening a Directory for Reading with opendir() 192 m er Reading Characters from a File with fgetc() 188 Writing or Appending to a File 189 Writing to a File with fwrite() or fputs() 189 Locking Files with flock() 190 cia l, Reading Arbitrary Amounts of Data from a File with fread() 186 http://i-tronics.blogspot.com/ us Including Files with include() 175 Testing Files 178 Checking for Existence with file_exists() 179 A File or a Directory? 179 Checking the Status of a File 179 Determining File Size with filesize() 180 Getting Date Information About a File 180 Creating a Function That Performs Multiple File Tests 181 Creating and Deleting Files 183 Opening a File for Writing, Reading, or Appending 183 Reading from Files 184 Reading Lines from a File with fgets() and feof() 185 e fo re du ca tio n on ly Redirecting the User 167 File Upload Forms and Scripts 169 Summary 173 Q&A 173 Workshop 173 Quiz 174 Activities 174 15 227 Listing the Tables Within a Database 229 Listing and Exploring Fields 229 Database Structure— Bringing It All Together 230 Summary 232 Q&A 233 Workshop 233 Quiz 234 235 No Activities 234 Hour 13: Beyond the Box Overview 235 tf or co Listing Databases m er Hour 12: Database Integration— MySQL213 Overview 213 A (Very) Brief Introduction to SQL 213 Connecting to the Database Server 214 Selecting a Database 215 Finding Out About Errors 215 Adding Data to a Table 216 Acquiring the Value of an Automatically Incremented Field 220 Accessing Information 221 Finding the Number of Rows Found by a Query 221 Accessing a Resultset 222 Changing Data 225 Getting Information About Databases 227 cia l, http://i-tronics.blogspot.com/ us e fo re du ca Overview 196 Opening a DBM Database 196 Adding Data to the Database 197 Amending Elements in a Database 198 Reading from a DBM Database 199 Determining Whether an Item Exists in a Database 201 Deleting an Item from a Database 201 Adding Complex Data Structures to a DBM Database 201 An Example205 Summary 211 Q&A 211 Workshop 211 Quiz 211 Activities 212 tio n on ly 16 m er Sending Mail with the mail() Function 252 Summary 253 Q&A 253 Workshop 254 Quiz 254 Activities 254 Hour 14: Working with Dynamic Images 256 Overview 256 Creating and Outputting Images 256 Acquiring Color 257 Drawing Lines 258 Applying Color Fills 259 Drawing an Arc 260 Drawing a Rectangle 261 Drawing a Polygon 262 Making a Color Transparent 263 Working with Text 264 Writing a String with imageTTFtext() 265 Testing Text Dimensions with imageTTFbox() cia l, us e Bringing It Together co 270 Summary 275 Q&A 275 Workshop 276 Quiz 276 Activities 276 Hour 15: Working with Dates Overview 277 No tf or 277 Getting the Date with time() 277 Converting a Time Stamp with getdate() 278 Converting a Time Stamp with date() 279 http://i-tronics.blogspot.com/ fo re du ca 266 tio n on ly Environmental Variables 235 A Brief Summary of an HTTP Client/Server Negotiation 238 The Request 238 The Response 241 Getting a Document from a Remote Address 243 Converting IP Addresses and Hostnames 244 Making a Network Connection 245 Making an NNTP Connection Using fsockopen() 249 17 Hour 16: Working with Data 294 Overview 294 Data Types Revisited 294 A Recap 294 Converting Complex Types 295 Automatic Conversion of Data Types 297 Testing Data Types 298 More Ways of Changing Type 300 Why Are Data Types Important? 300 Testing for Absence and Emptiness 302 More About Arrays 303 An Alternative Approach to Traversing Arrays 304 Checking That a Value Exists in an Array 305 Removing an Element from an Array 306 Applying a Function to Every Element in an Array 306 Custom Sorting Arrays 307 Summary 311 Q&A 311 311 Quiz 311 Activities 312 Hour 17: Working with Strings 313 Overview 313 Formatting Strings 313 No tf or Workshop co Working with printf() 313 printf() and Type Specifiers 314 Padding Output with the Padding Specifier 317 m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio Creating Time Stamps with mktime() Testing a Date with checkdate() An Example283 Checking User Input 284 Building the HTML Form 285 Creating the Calendar Table287 Summary 292 Q&A 292 Workshop 292 Quiz 292 Activity 293 282 283 n on ly 18 m er Hour 18: Working with Regular Expressions 334 Overview 334 POSIX Regular Expression Functions 334 Using ereg() to Match Patterns in Strings cia l, Specifying a Field Width 318 Specifying Precision 319 Conversion Specifications: A Recap 320 Storing a Formatted String 322 Investigating Strings 323 A Note About Indexing Strings 323 Finding the Length of a String with strlen() 324 Finding a Substring Within a String with strstr() 324 Finding the Position of a Substring with strpos() 325 Extracting Part of a String with substr() 325 Tokenizing a String with strtok() 326 Manipulating Strings 328 Cleaning Up a String with trim() and ltrim()328 Replacing a Portion of a String using substr_replace() 329 Replacing Substrings Using str_replace 329 Converting Case 329 Breaking Strings into Arrays with explode() 331 Summary 331 Q&A 332 Workshop 332 Quiz 332 Activities 333 us e No tf or co Using Quantifiers to Match a Character More Than Once 335 Matching Ranges of Characters with Character Classes 338 Working with Atoms 339 Branches 340 Anchoring a Regular Expression 340 342 The Membership Code Example Revisited 341 Using egrep_replace() to Replace Patterns in Strings Using Back References with egrep_replace() 342 Using split() to Break Up Strings 343 Perl Compatible Regular Expressions (PCREs) 343 Matching Patterns with preg_match() 343 http://i-tronics.blogspot.com/ fo re du ca 335 tio n on ly 19 Hour 19: Saving State with Cookies and Query Strings 356 Overview 356 Cookies 356 The Anatomy of a Cookie 357 Setting a Cookie with PHP 358 Deleting a Cookie 360 Creating Session Cookies 360 An Example— Tracking Site Usage 361 Working with the Query String 369 Creating a Query String370 Summary 372 Q&A 373 Workshop 373 Quiz 373 Activities 374 Hour 20: Saving State with Session Functions 375 Overview 375 What Are Session Functions? 375 Starting a Session with session_start() 376 No tf or Working with Session Variables 377 Destroying Sessions and Unsetting Variables 382 Passing Session IDs in the Query String 383 384 Checking that a Session Variable Is Registered 385 Summary 385 Q&A 386 Workshop Quiz 386 386 Encoding and Decoding Session Variables co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n PCREs and Greediness 344 PCREs and Backslashed Characters 345 Finding Matches Globally with preg_match_all() Using preg_replace() to Replace Patterns 350 Modifiers 351 Summary 354 Q&A 354 Workshop 355 Quiz 355 Activity 355 347 on ly 20 Activities 386 Hour 21: Working with the Server Environment 388 Overview 388 Opening Pipes to and from Processes with popen() 388 Running Commands with exec() 392 Running External Commands with system() or the Backtick Operator 393 Plugging Security Holes with escapeshellcmd() 394 Running External Applications with passthru() 396 Calling an External CGI Script with the virtual() Function 397 Summary 398 Q&A 398 Workshop 399 Quiz 399 Activities 400 Hour 22: Debugging 401 Overview 401 Getting Information About PHP and Your Script 401 phpinfo() 401 Viewing Source with Syntax Coloring 405 PHP Error Messages 407 Writing Error Messages to a Log File 410 Getting the Error String 412 Manual Debugging 412 Common Errors 414 Summary 416 Q&A 417 Workshop 417 417 Activity 417 Hour 23: An Example (Part 1) 418 Overview 418 The Brief 418 The Structure 418 Designing the Database419 No tf or Design Choices 421 The Members Environment 421 join.php and dblib.inc 421 co Quiz m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 21 No tf or co m er cia l, Hour 24: An Example (Part 2) 457 Overview 457 The Events Diary Public Screens viewevents.php 457 viewclubs.php 466 viewclub.php 470 viewevent.php 473 The Future 476 Summary 477 Q&A 477 Workshop 477 Quiz 477 Activities 478 http://i-tronics.blogspot.com/ us e fo re du ca 457 tio n updateclub.php 429 membersmenu.php 437 login.php 438 updateevent.php 441 reviewevents.php 450 Summary 455 Q&A 455 Workshop 456 Quiz 456 Activity 456 on ly 22 Hour 1: PHP: From Home Page to Portal Welcome to PHP! Throughout this book you will look at almost every element of the future. In this hour, you will learn What PHP is About PHP's history PHP language. But first you will explore PHP as a product— its history, features, and What improvements can be found in PHP4 Some options that add features to your PHP binary Some reasons you should choose to work with PHP PHP is a language that has outgrown its name. It was originally conceived as a set of macros to help coders maintain personal home pages, and its name grew from its purpose. Since then, PHP's capabilities have been extended, taking it beyond a set database-driven online environments. As PHP's capabilities have grown, so too has its popularity. According to NetCraft (http://www.netcraft.com), PHP was running on more than 1 million hosts in November 1999. As of February 2000, that figure had already risen to 1.4 million hosts. According to E-Soft, PHP is the most popular Apache module available, beating even ModPerl. of utilities to a full-featured programming language, capable of managing huge No PHP is now officially known as PHP: HyperText Preprocessor. It is a server-side scripting language usually written in an HTML context. Unlike an ordinary HTML page, a PHP script is not sent directly to a client by the server; instead, it is parsed by the PHP binary or module. HTML elements in the script are left alone, but PHP code is interpreted and executed. PHP code in a script can query databases, create images, read and write files, talk to remote servers— the possibilities are endless. tf or co m er cia l, http://i-tronics.blogspot.com/ us What Is PHP? e fo re du ca tio n on ly Overview 23 The output from PHP code is combined with the HTML in the script and the result sent to the user. How Did PHP Evolve? publishing macros. These were released as the Personal Home Page Tools and later From a user's perspective, PHP/FI was already an attractive proposition, and its community. By 1997, a team of programmers was working on the project. The next release— PHP3— was born out of this collaborative effort. PHP3 was an rewritten and extended to include a package called the Form Interpreter (PHP/FI). popularity grew steadily. It also began to attract interest from the developer effective rewrite of PHP, with an entirely new parser created by Zeev Suraski and Andi Gutmans, as well as differences in syntax and new features. This release established PHP as one of the most exciting server scripting languages available, and the growth in usage was enormous. module. MySQL is a powerful free SQL database, and PHP provides a comprehensive all but unbeatable. That isn't to say that PHP is not designed to work in other environments and with other tools. In fact, PHP supports a bewildering array of databases and servers. The rise in popularity of PHP has coincided with a change of approach in Web publishing. In the mid-1990s it was normal to build sites, even relatively large sites, with hundreds of individual hard-coded HTML pages. Increasingly, though, site publishers are harnessing the power of databases to manage their content more effectively and to personalize their sites according to individual user preferences. No The use of databases to store content, and of a scripting language to retrieve this data, will become further necessary as data is sent from a single source to multiple environments, including mobile phones and PDAs, digital television, and broadband Internet environments. In this context, it is not surprising that a tool of PHP's sophistication and flexibility is becoming so popular. tf or co m er cia l, set of functions for working with it. The combination of Apache, MySQL, and PHP is http://i-tronics.blogspot.com/ us the most-used Web server in the world, and PHP3 can be compiled as an Apache e PHP's support for Apache and MySQL further secured its popularity. Apache is now fo re du ca tio n on ly The first version of PHP was created by Rasmus Lerdorf in 1994 as a set of Web 24 At the time of this writing, PHP4 is in its final beta stage and is due for release shortly. By the time you read this book, PHP4 will be making waves! What's New in PHP4 interesting. Let's take a quick look at some of them. A new foreach statement, similar to that found in Perl, makes it much easier to book. Additionally, a raft of new array functions have been added, making arrays easier to manipulate. The language now includes the boolean data type. A particularly useful feature of PHP3 was the capability to name form elements as if they were elements in an array. The elements' names and values are then made available to the code in array form. This feature has been extended to support multidimensional arrays. Support for object-oriented programming was somewhat rudimentary in PHP. This is significantly extended in PHP4; for example, it is now possible to call an overridden method from a child class. PHP4 now provides native support for user sessions, using both cookies and the query string. You can now "register" a variable with a session, and then access the same variable name and value in subsequent user requests. A new comparison operator (===) has been introduced that tests for New associative arrays containing server and environmental variables have been made available, as well as a variable that holds information about uploaded PHP4 now provides built-in support for both Java and XML. Although these and other features significantly improve the language, perhaps the files. equivalence of type as well as equivalence of value. No The Zend Engine When PHP3 was written, an entirely new parser was created from the ground up. PHP4 represents a similar change to the scripting engine. This rewrite, though, is more significant by orders of magnitude. tf most significant change has taken place under the hood. or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n loop through arrays. We will be using this for most of the array examples in this on ly PHP4 introduces numerous new features that will make the programmer's life more 25 Zend is a scripting engine that sits below the PHP-specific modules. It is optimized to significantly improve performance. These changes in efficiency will ensure PHP4's continued success. Most code written for PHP3 will continue to run with no changes; however, these scripts may run up to 200 times faster! A commercial addition to the Zend engine will be the facility for compiling PHP all, competitors far behind. scripts. This will provide a further gain in performance that should leave most, if not Communication with servers has been improved, so it will be possible to create PHP modules that work with a wider range of servers. Unlike a CGI interpreter, which sits outside a server and is initialized every time a script is run, a server module runs in conjunction with the server. This improves performance because the scripting engine does not need to be started for a PHP page to be executed. Why Choose PHP? There are some compelling reasons to work with PHP4. For many projects you will find that the production process is significantly faster than you might expect if you are used to working with other scripting languages. As an open source product, PHP4 is well supported by a talented production team and a committed user community. Furthermore, PHP can be run on all the major operating systems with most servers. Because PHP allows you to separate HTML code from scripted elements, you will instances, you will be able to separate the coding stage of a project from the design and build stages. Not only can this make life easier for you as a programmer, it also can remove obstacles that stand in the way of effective and flexible design. No tf notice a significant decrease in development time on many projects. In many or co Speed of Development m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio Zend is built to improve performance but is also designed for increased flexibility. n on ly 26 PHP Is Open Source To many people, "open source" simply means free, which is, of course, a benefit in itself. To quote from the official PHP site at http://www.php.net/: background, but PHP doesn't cost anything. You can use it for commercial and/or non-commercial use all you want. You can give it to your friends, print it out and This may sound a little foreign to all you folks coming from a non-UNIX license. Well-maintained open source projects offer users additional benefits, though. You benefit from an accessible and committed community who offer a wealth of experience in the subject. Chances are that any problem you encounter in your coding can be answered swiftly and easily with a little research. If that fails, a question sent to a mailing list can yield an intelligent, authoritative response. You also can be sure that bugs will be addressed as they are found, and that new the next commercial release before taking advantage of improvements. There is no vested interest in a particular server product or operating system. You are free to make choices that suit y our needs or those of your clients, secure that your code will run whatever you decide. Performance Because of the powerful Zend engine, PHP4 compares well with ASP in benchmark tests, beating it in some tests. Compiled PHP leaves ASP far behind. Portability No PHP is designed to run on many operating systems and to cooperate with many servers and databases. You can build for a UNIX environment and shift your work to NT without a problem. You can test a project with Personal Web Server and install it on a UNIX system running on PHP as an Apache module. tf or co m er cia l, http://i-tronics.blogspot.com/ us features will be made available as the need is defined. You will not have to wait for e fo re du ca tio software! Smile, be happy, the world is good. For the full legalese, see the official n hang it on your wall or eat it for lunch. Welcome to the world of Open Source on ly 27 Summary In this hour, we introduced PHP. You learned the history of PHP from a simple set of macros to the powerful scripting environment it has become. You found out about PHP4 and the Zend scripting engine, and how they incorporate new features and more efficiency. Finally, you discovered some of the features that make PHP a compelling choice as a Web programming language. Q Is PHP an easy language to learn? A In short, yes! You really can learn the basics of PHP in 24 hours. PHP provides an enormous wealth of functions that allow you to do things for which you would have to write custom code in other languages. PHP also handles data types and memory issues for you (much like Perl). Understanding the syntax and structures of a programming language is only the beginning of the journey, however. Ultimately, you will only really learn by building your own projects and by making mistakes. You should see this book as a starting point. Workshop material covered. Try to understand the quiz answers before continuing to the next hour's lesson. Quiz answers are provided in Appendix A. Quiz No tf What did the initials PHP originally stand for? Who created the original version of PHP? What is the name of the new scripting engine that powers PHP? Name a new feature introduced with PHP4. or co m er The Workshop provides quiz questions to help you solidify your understanding of the cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n Q&A on ly 28 Activity Flick through this book to get an idea of its structure. Think about the topics covered and how they might help you with any future projects. No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 29 Hour 2: Installing PHP Overview Before getting started with the PHP language, you must first acquire, install, and works in conjunction with many servers. In this hour, you will learn Where to find PHP and other useful open source software One way of installing PHP on Linux Some configuration directives How to find help when things go wrong Some options that add features to your PHP binary configure the PHP interpreter. PHP is available for a wide range of platforms and PHP is truly cross-platform. It runs on the Windows operating system, most versions of UNIX including Linux, and even the Macintosh. Support is provided for a range of Web servers including Apache (itself open source and cross-platform), Microsoft Personal Web Server. The latter is useful if you want to test your scripts offline on a Windows machine, although Apache can also be run on Windows. You can also compile PHP as a standalone application. You can then call it from the command line. In this book, we will concentrate on building Web applications, but do not underestimate the power of PHP4 as a general scripting tool comparable to Perl. Internet Information Server, WebSite Pro, the iPlanet Web Server, and Microsoft's No PHP is designed to integrate easily with databases. This feature is one of the factors that make the language such a good choice for building sophisticated Web applications. Many databases are directly supported, including Adabas D, InterBase, Solid, dBASE, mSQL, Sybase, Empress, MySQL, Velocis, FilePro, Oracle, UNIX dbm, Informix, and PostgreSQL. PHP also supports ODBC. tf or co m er cia l, http://i-tronics.blogspot.com/ us Platforms, Servers, Databases, and PHP e fo re du ca Which platforms, servers, and databases are supported by PHP4 tio n on ly 30 Throughout this book, we will be using a combination of Linux, Apache, and MySQL. All these are free to download and use, and can be installed relatively easily on a PC. You on can a find Power out PC, more you about can getting find Linux for your about computer LinuxPPC at at . If you want to run Linux information . MySQL, the database we will use in this book, can be downloaded from including UNIX, Windows, and OS/2. . There are versions for many operating systems On the other hand, you can easily stick with Windows, NT, or MacOS. PHP is, after Where to Find PHP and More You can find PHP4 at . PHP4 is open source software, which means that you won't need your credit card handy when you download it. read online at , complete with helpful annotations from other PHP coders. You can also download the manual in several formats. Installing PHP4 for Linux and Apache In this section, we will look at one way of installing PHP4 with Apache on Linux. The process is more or less the same for any UNIX operating system. You might be able to find prebuilt versions of PHP for your system, which are simple to install. Compiling PHP, though, gives you greater control over the features built in to your binary. Before you install you should make sure that you are logged into your system as the No root user. If you are not allowed access to your system's root account, you may need to ask your system administrator to install PHP for you. There are two ways of compiling an Apache PHP module. You can either recompile Apache, statically linking PHP into it, or you can compile PHP as a Dynamic Shared Object (DSO). If your version of Apache was compiled with DSO support, it will be capable of supporting new modules without the need for recompiling the server. tf or co m er cia l, http://i-tronics.blogspot.com/ us e The PHP WebSite is an excellent resource for PHP coders. The entire manual can be fo re du ca all, a cross-platform scripting language. tio n on ly 31 This method is the easiest way to get PHP up and running, and it is the one we will look at in this section. In order to test that Apache supports DSOs you should launch the Apache binary (httpd) with the -l argument. /www/bin/httpd -l You should see a list of modules. If you see mod_so.c Apache. The Apache distribution contains full instructions for this. If you have not already done so, you will need to download the latest distribution of PHP4. Your distribution will be archived as a tar file and compressed with gzip, so you will need to unpack it: tar -xvzf php-4.0.tar.gz After your distribution is unpacked, you should move to the PHP4 distribution arguments that will control the features that PHP will support. For this example, we will include some useful command line arguments, although you might want to available to you later in the hour. ./configure --enable-track-vars \ --with-gd \ --with-mysql \ specify arguments of your own. We will discuss some of the configure options No The path you assign to the --with-apxs argument is likely to be different on your system. It is possible that you will find apxs in the same directory as your Apache executable. After the configure script has run, you can run the make program. You will need a C compiler on your system to run this command successfully. make tf or co --with-apxs=/www/bin/apxs m er cia l, Within your distribution directory you will find a script called configure. This accepts http://i-tronics.blogspot.com/ us cd ../php-4.0 e directory: fo re du ca tio among them, you should be able to proceed; otherwise, you may need to recompile n on ly 32 make install These commands should end the process of PHP4 compilation and installation. You should now be able to configure and run Apache. When we ran the configure script, we included some command-line arguments script itself gives you a list of available options. From the PHP distribution directory type the following: ./configure --help that determined the features that the PHP interpreter will include. The configure The list produced is long, so you may want to add it to a file for reading at leisure: ./configure --help > configoptions.txt Although the output from this command is very descriptive, we will look at a few useful options— especially those that might be needed to follow this book. --enable-track-vars This option automatically populates associative arrays with values submitted as part of GET, POST requests or provided in a cookie. You can read more about arrays in good idea to include this option when running configure. --with-gd Hour 7, "Arrays," and about HTTP requests in Hour 13, "Beyond the Box." It is a --with-gd enables support for the GD library, which, if installed on your system, more about creating dynamic images in Hour 14, "Working with Dynamic Images." You can optionally specify a path to your GD library's install directory: --with-gd=/path/to/dir No tf allows you to create dynamic GIF or PNG images from your scripts. You can read or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly Some configure Options 33 --with-mysql --with-mysql enables support for the MySQL database. If your system has MySQL installed in a directory other than the default location, you should specify a path: --with-mysql=/path/to/dir As you know, PHP provides support for other databases. Table 2.1 lists some of Table 2.1: Some Database configure Options Database Adabas D FilePro msql informix iODBC OpenLink ODBC Oracle PostgreSQL Solid Sybase Sybase-CT Velocis LDAP configure Option --with-adabas --with-filepro --with-msql --with-informix --with-iodbc --with-openlink --with-oracle --with-pgsql --with-solid or tf No Configuring Apache After you have compiled PHP and Apache, you should check Apache's configuration file, httpd.conf, which you will find in a directory called conf in the Apache install directory. Add the following lines to this file: co m er --with-sybase --with-sybase-ct --with-velocis --with-ldap cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n them and the configure options you will need to use them. on ly 34 AddType application/x-httpd-php .php AddType application/x-httpd-php-source .phps This ensures that the PHP interpreter will parse files that end with the .php extension. Any files with the .phps extension will be output as PHP source. That is, the source code will be converted to HTML and color-coded. This can be useful for debugging your scripts. If you want to offer to your users PHP pages with extensions more familiar to them, the .html extension are treated as PHP files with the following: AddType application/x-httpd-php .html Note that treating files with the .html extension as PHP scripts could slow down your site, because every page with this extension will be parsed by the PHP interpreter before it is served to the user. If PHP has been preinstalled and you have no access to the Apache configuration files, you may be able to change the extensions that will determine which files will called .htaccess. After you have created this file, the directive will affect the enclosing directory, as well as any subdirectories. This technique will only work if the AllowOverride directive for the enclosing directory is set to either FileInfo or All. Although the filename .htaccess is the default for an access control file, it may have you don't have root access, you should be able to read the Apache configuration files. be treated as PHP executables by including an AddType directive in a file An .htaccess file can be an excellent way of customizing your server space if you do not have access to the root account. An additional way of controlling the behavior of PHP, even as a non-root user, is the php.ini file. No php.ini After you have compiled or installed PHP, you can still change its behavior with a file called php.ini. On UNIX systems, the default location for this file is /usr/local/lib; on a Windows system, the default location is the Windows directory. A php.ini file in the current working directory will override one in the default location, so you can change the behavior of PHP on a per-directory basis. tf or co m er been changed. Check the AccessFileName directive in httpd.conf to find out. Even if cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n you can choose any extension you want. You can even ensure that files with on ly 35 You should find a sample php.ini file in your distribution directory, which contains factory settings. Factory settings will be used if no php.ini file is used. The default settings should be adequate for most of the examples in this book, although you can read about some amendments you might like to make in Hour 22, "Debugging." Directives in the php.ini file take the form of a directive and a value separated by an equals sign. Whitespace is ignored. can create one in your script's directory that can override the default. You can also set an environmental variable PHPRC that designates a php.ini file. You can change your php.ini settings at any time, though if you are running PHP as an Apache module, you should restart the server for the changes to take effect. short_open_tag code with the symbols . If this has been disabled, you will see short_open_tag = Off short_open_tag = No short_open_tag = On short_open_tag = True No You can read more about PHP open and close tags in Hour 3, "A First Script." Error Reporting Directives To diagnose bugs in your code, you should enable the directive that allows error messages to be written to the browser. This is on by default: tf short_open_tag = Yes or co To enable the directive you can use one of the following: m er short_open_tag = False cia l, one of the following: http://i-tronics.blogspot.com/ us The short_open_tag directive determines whether you can begin a block of PHP e fo re du ca tio settings in php.ini. Remember, if you are not allowed to alter this document, you n If PHP has been preinstalled on your system, you might want to check some of the on ly 36 display_errors = On You can also set the level of error reporting. We will cover the options available for the error_reporting directive in more depth in Hour 22. For now, however, you should set this to the following: error_reporting = E_ALL & ~ E_NOTICE This will report all errors but not notices that warn about potential problems with your code. Notices can interfere with some PHP techniques. This setting is the default. Variable Directives PHP makes certain variables available to you as a result of a GET request, a POST request, or a cookie. You can influence this in the php.ini file. The track_vars directive creates associative arrays containing elements generated as a result of an HTTP request. This is allowed by default: The register_globals directive determines whether values resulting from an HTTP request should be made available as global variables. Many scripts in this book will require the following setting to be enabled: register_globals = On Help! Help is always at hand on the Internet, particularly for problems concerning open matter how intractable your installation, configuration, or programming problem might seem, chances are you are not alone. Someone will have already answered your question. When you hit a brick wall, your first recourse should be to the official PHP site at , particularly the annotated manual at . If you still can't find your answer, don't forget that the PHP site is searchable. The advice you are seeking may be lurking in a press release or a Frequently Asked No tf or source software. Wait a moment before you hit the send button, however. No co m er cia l, http://i-tronics.blogspot.com/ us e track_vars = On fo re du ca tio n on ly 37 Questions file. Another excellent and searchable resource is the PHP Knowledge Base at . Still no luck? You can find links to searchable mailing list archives at . These archives represent a huge information resource with contributions from many of the great and the good in the If you are still convinced that your problem has not been addressed, you may well be doing the PHP community a service by exposing it. Although these lists are often high volume, you can learn a lot from them. If you are serious about PHP scripting, you should certainly subscribe at least to a digest list . Once subscribed to the list that matches your concerns, you might consider posting your problem. When you post a question it is often a good idea to include as much information as possible (without writing a novel). The following items often are pertinent: Your operating system The configure options you chose failure Any output from the configure or make commands that preceded an installation A reasonably complete example of the code that is causing you problems research skills will stand you in good stead. A good researcher can generally solve a problem quickly and efficiently. Asking a naive question of a technical list often involves a wait rewarded only by a message or two referring you to the archives where you should have begun your search for answers. Second, remember that a mailing list is not analogous to a technical support call center. No one is paid to answer your questions. Despite this, you have access to an No impressive resource of talent and knowledge, including that of some of the creators of PHP itself. A good question and its answer will be archived to help other coders. Asking a question that has been answered several times just adds more noise. Having said this, don't be afraid to post a problem to the list. PHP developers are a civilized and helpful breed, and by bringing a problem to the attention of the community, you might be helping others to solve the same problem. tf or co m er Why all these cautions about posting a question to a mailing list? First, developing cia l, http://i-tronics.blogspot.com/ us e The version of PHP you are running or installing fo re du ca tio You can join the PHP mailing lists at . n on ly PHP community. Spend some time trying out a few keyword combinations. 38 Summary PHP4 is open source software. It is also open in the sense that it does not demand that you use a particular server, operating system, or database. In this hour, you learned where to locate PHP and other open source software that can help you host and serve Web sites. You learned how to compile PHP as an distribution will contain step-by-step instructions. You learned some of the configure options that can change the features that your binary will support. You about sources of support. You should now be ready to come to grips with the language itself. learned about php.ini and some of the directive it contains. Finally, you learned Apache module on Linux. If you download a PHP binary for another platform, your Q&A Q You have covered an installation for Linux and Apache. Does that mean A No, one of PHP's great strengths is that it runs on multiple platforms. If you are don't forget to read the files that come with your PHP distribution. You should find comprehensive step-by-step instructions for installation. If you are still having problems, review the "Help!" section earlier in this hour. The online resources mentioned there will almost certainly contain the answers you need. No material covered. Try to understand the quiz answers before continuing to the next hour's lesson. Quiz answers are provided in Appendix A. Quiz Where can you find the PHP online manual? From a UNIX operating system, how would you get help on configuration options (the options that you pass to the configure script in your PHP distribution)? http://i-tronics.blogspot.com/ tf The Workshop provides quiz questions to help you solidify your understanding of the or Workshop co m er cia l, having trouble installing PHP to work on your operating system or with your server, us that this book will not apply to my server and operating system? e fo re du ca tio n on ly 39 What is Apache's configuration file typically called? What line should you add to the Apache configuration file to ensure that the .php extension is recognized? What is PHP's configuration file called? Activity Install PHP on your system. If it is already in place, review your php.ini file and check your configuration. No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 40 Hour 3: A First Script Overview Having installed and configured PHP, it is now time to put it to the test. In this hour, you will create your first script and spend a little time analyzing its syntax. By the end of the hour, you should be ready to create documents that include both HTML In this hour, you will learn How to create, upload, and run a PHP script How to incorporate HTML and PHP in the same document How to make your code clearer with comments Let's jump straight in with a PHP script. To begin, open your favorite text editor. Like text editor, such as Notepad on Windows, Simple Text and BBEdit on MacOS, or VI and Emacs on UNIX operating systems. Most popular HTML editors provide at least some support for PHP. Type in the example in Listing 3.1 and save the file, calling it something like first.php. Listing 3.1: A First PHP Script 1: Figure 3.1 shows the script created in Listing 3.1 as typed into the BBEdit text editor for MacOS. tf or print "Hello Web!"; co m er cia l, HTML documents, PHP files are made up of plain text. You can create them with any http://i-tronics.blogspot.com/ us Our First Script e fo re du ca and PHP. tio n on ly 41 Figure 3.1: Your first script as created in the BBEdit text editor. the file as PHP code and invoke the interpreter. The default PHP extension for a PHP 4 document is .php. This can be changed, however, by altering the server's configuration. You saw how to do this in Hour 2, "Installing PHP." If you are not working directly on the machine that will be serving your PHP script, you will probably need to use an FTP client, such as WS-FTP for Windows or Fetch for MacOS to upload your saved document to the server. from the first.php script. Figure 3.2: Success: the output from Listing 3.1. No If PHP is not installed on your server or your file's extension is not recognized, you may not see the output shown in Figure 3.2. In these cases, you probably will see the source code created in Listing 3.1. Figure 3.3 shows what happens when an unknown extension is encountered. tf or co m er cia l, http://i-tronics.blogspot.com/ us all has gone well, you should see the script's output. Figure 3.2 shows the output e After the document is in place, you should be able to access it via your browser. If fo re du ca tio The extension to the PHP document is important because it tells the server to treat n on ly 42 Figure 3.3: Failure: the extension is not recognized. If this happens, first check the extension with which you saved your PHP script. In Figure 3.3, the document was accidentally called first.nphp. If the file extension is as it should be, you may need to check that PHP has been installed properly and that your server is configured to work with the extension that you have used for your script. You can read more about installing and configuring PHP in Hour 2. Now that you have uploaded and tested your script, you can take a look at the code Beginning and Ending a Block of PHP Statements When writing PHP, you need to inform the interpreter that you want it to execute and will be output to the browser. Table 3.1 shows the four ways of enclosing PHP code. Table 3.1: PHP Start and End Tags tags No Short tags ASP tags Script tags tf Standard or Tag Style co m er your commands. If you don't do this, the code you write will be mistaken for HTML Start Tag cia l, http://i-tronics.blogspot.com/ us e in a little more detail. End Tag ?> ?> %> fo re du ca tio n on ly 43 Of the tags in Table 3.1, only the standard and the script tags can be guaranteed to work on any configuration. The short and ASP style tags must be explicitly enabled in your php.ini. You examined the php.ini file in Hour 2. To activate recognition for short tags, you must make sure that the short_open_tag switch is set to "On" in php.ini: short_open_tag = On; Short tags are enabled by default, so you would only need to edit php.ini if you want To activate recognition for the ASP style tags, you must enable the asp_tags asp_tags = On; After you have edited php.ini, you should be able to choose from any of the four styles for use in your scripts. This is largely a matter of preference, although if you intend to work with XML, you should disable the short tags ( ) and work with the standard tags (). Let's run through some of the ways in which you can legally write the code in Listing 3.1. You could use any of the four PHP start and end tags that you have seen: print("Hello Web!"); ?> <% No %> Single lines of code in PHP also can be presented on the same line as the PHP start and end tags: tf print("Hello Web!"); or co m er cia l, Now that you know how to define a block of PHP code, take a closer look at the code in Listing 3.1 itself. The print() Function print() is a function that outputs data. In most cases, anything output by print() ends up in the browser window. A function is a command that performs an action, usually modified in some way by data provided for it. Data sent to a function is almost always placed in parentheses after the function name. In this case, you sent enclosed by quotation marks, either single or double. the print() function a collection of characters, or string. Strings must always be Note Function calls generally require parentheses after their name whether or not they demand that data be passed to them. print() is an exception, and enclosing the data you want to print to the browser in parentheses is optional. This is the more common syntax, so we will usually omit the brackets in our examples. informs the interpreter that you have completed a statement. TERM is to PHP what a sentence is to written or spoken English. A statement should usually end with a semicolon; a sentence should enclose other statements, and statements that end a block of code. In most cases, however, failure to end a statement with a semicolon end with a period. Exceptions to this include statements that semicolon is optional. No Combining HTML and PHP The script in Listing 3.1 is pure PHP. You can incorporate this into an HTML document simply by adding HTML outside the PHP start and end tags, as shown in Listing 3.2. Listing 3.2: A PHP Script Including HTML 1: 2: tf or Because the statement in Listing 3.1 is the final one in that block of code, the co will confuse the interpreter and result in an error. m er cia l, NEW A statement represents an instruction to the interpreter. Broadly, it http://i-tronics.blogspot.com/ us You ended your only line of code in Listing 3.1 with a semicolon. The semicolon e fo re du ca tio n on ly 45 3: 4: 5: 6: 7: 10: 11: 12: print "hello world"; typing in the code. The PHP interpreter ignores everything outside PHP open and close tags. If you were to view Listing 3.2 with a browser, as shown in Figure 3.4, you would see the string "hello world" in bold. If you were to view the document source, as shown in Figure 3.5, the listing would look exactly like a normal HTML document. You can include as many blocks of PHP code as you need in a single document, code in a single document, they combine to form a single script. Anything defined in the first block (variables, functions, or classes, for example) usually will be available to subsequent blocks. No Figure 3.4: The output of Listing 3.2 as viewed in a browser. tf or co m er cia l, http://i-tronics.blogspot.com/ us e interspersing them with HTML as required. Although you can have multiple blocks of fo re du ca As you can see, incorporating HTML into a PHP document is simply a matter of tio n on ly 46 Figure 3.5: The output of Listing 3.2 as HTML source code. Adding Comments to PHP Code Code that seems clear at the time of writing, can seem like a hopeless tangle when can save you time later on and make it easier for other programmers to work with your code. NEW TERM A comment is text in a script that is ignored by the interpreter. Comments can be used to make code more readable, or to annotate a script. All text from either of these marks until either the end of the line or the PHP close tag is ignored. # // this is a comment this is another comment Multiline comments begin with a forward slash followed by an asterisk (/*) and end /* No this is a comment none of this will be parsed by the interpreter * tf with an asterisk followed by a forward slash (*/). / or co m er Single line comments begin with two forward slashes (/ /) or a single hash sign (#). cia l, http://i-tronics.blogspot.com/ us e you come to amend it six months later. Adding comments to your code as you write fo re du ca tio n on ly 47 Summary You should now have the tools at your disposal to run a simple PHP script on a properly configured server. In this hour, you created your first PHP script. You learned how to use a text editor use to begin and end blocks of PHP code. You learned how to use the print() function to send data to the browser, and you brought HTML and PHP together into the same documents. script. Finally, you learned about comments and how to add them to PHP Q&A Q Which are the best start and end tags to use? A It is largely a matter of preference. For the sake of portability the standard tags () are probably the safest bet. Short tags are enabled by default and have the virtue of brevity. example). Even if you save files created using this type of editor in plain text format, hidden characters are likely to creep into your code. Q When should I comment my code? A This is a matter of preference once again. Some short scripts will be self-explanatory to you, even after a long interval. For scripts of any length or complexity, you should comment your code. This often saves you time and frustration in the long run. No Workshop The Workshop provides quiz questions to help you solidify your understanding of the material covered. Try to understand the quiz answers before continuing to the next hour's lesson. Quiz answers are provided in Appendix A. tf or co m er cia l, A Do not use word processors that format text for printing (such as Word, for http://i-tronics.blogspot.com/ us Q What editors should I avoid when creating PHP code? e fo re du ca tio n on ly to create and name a PHP document. You examined four sets of tags that you can 48 Quiz Can a user read the source code of PHP script you have successfully installed? What do the standard PHP delimiter tags look like? What do the ASP PHP delimiter tags look like? What do the script PHP delimiter tags look like? What function would you use to output a string to the browser? Activity scripts. No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca Familiarize yourself with the process of creating, uploading, and running PHP tio n on ly 49 Hour 4: The Building Blocks Overview In this hour, you are going to get your hands dirty with some of the nuts and bolts of the language. bombarded with information. Don't worry— you can always refer back here later on. If you're already an experienced programmer, you should at least skim this hour's lesson. It covers a few PHP-specific features. In this hour, you will learn How to define and access variables About data types About variables— what they are and how to use them How to use operators to create expressions Variables A variable is a special container that you can define to "hold" a value. A variable consists of a name that you can choose, preceded by a dollar ($) sign. The variable names cannot include spaces or characters that are not alphanumeric. The following code defines some legal variables: $a; $a_longish_variable_name; name can include letters, numbers, and the underscore character (_). Variable No $2453; $sleepyZZZZ Remember that a semicolon (;) is used to end a PHP statement. The semicolons in the previous fragment of code are not part of the variable names. NEW TERM A variable is a holder for a type of data. It can hold numbers, strings of characters, objects, arrays, or booleans. The contents of a variable can be changed at any time. tf or co m er cia l, How to define and use constants http://i-tronics.blogspot.com/ us About some of the more commonly used operators e fo re du ca Concentrate on understanding rather than memorizing the features covered. tio n There's a lot of ground to cover, and if you are new to programming, you might feel on ly 50 As you can see, you have plenty of choices about naming, although it is unusual to see a variable name that consists exclusively of numbers. To declare a variable, you need only to include it in your script. You usually declare a variable and assign a value to it in the same statement. $num1 = 8; $num2 = 23; The preceding lines declare two variables, using the assignment operator (=) to give them values. You will learn about assignment in more detail in the Operators and Expressions section later in the hour. After you give your variables values, you print $num1; is equivalent to print 8; as long as $num1 contains 8. Dynamic Variables As you know, you create a variable with a dollar sign followed by a variable name. Unusually, the variable name can itself be stored in a variable. So, when assigning $user = "bob"; is equivalent to $holder="user"; $$holder = "bob"; a value to a variable The $holder variable contains the string "user", so you can think of $$holder as a Note You can use a string constant to define a dynamic variable instead of a variable. To do so, you must wrap the string you want to use for the variable name in braces: ${"user"} = "bob"; No When accessing a dynamic variable, the syntax is exactly the same: $user ="bob"; print $user; is equivalent to $user ="bob"; $holder="user"; tf or This might not seem useful at first glance. However, by using the concatenation operator and a loop (see Hour 5, "Going with the Flow"), you can use this technique to create tens of variables dynamically. co m er dollar sign followed by the value of $holder. PHP interprets this as $user. cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n can treat them exactly as if they were the values themselves. In other words on ly 51 print $$holder; If you want to print a dynamic variable within a string, however, you need to give the interpreter some help. The following print statement: $user="bob"; $holder="user"; print "$$holder"; does not print "bob" to the browser as you might expect. Instead it prints the strings "$" and "user" together to make "$user". When you place a variable within quotation marks, PHP helpfully inserts its value. In this case, PHP replaces $holder that a variable within a string is part of a dynamic variable, you must wrap it in $user="bob"; $holder="user"; print "${$holder}"; now prints "bob", which is the value contained in $user. Listing 4.1 brings some of the previous code fragments together into a single script using a string stored in a variable to initialize and access a variable called $user. 1: 2: 4: 5: 6: "; 15: print $$holder; 16: print "
"; tf or co 17: print "${$holder}
"; // prints "bob" 18: print "${'user'}
"; 19: ?> // prints "bob" m er cia l, 3: // prints "bob" // prints "bob" http://i-tronics.blogspot.com/ us e fo re du ca braces. The print statement in the following fragment: tio n with the string "user". The first dollar sign is left in place. To make it clear to PHP on ly 52 20: 21: References to Variables By default, variables are assigned by value. In other words, if you were to assign $aVariable to $anotherVariable, a copy of the value held in $aVariable would be stored in $anotherVariable. Subsequently changing the value of $aVariable would have no effect on the contents of $anotherVariable. Listing 4.2 illustrates this. Listing 4.2: Variables Are Assigned by Value 1: 2: 4: 5: 6: 13: 14: 3: 9: // a copy of the contents of $aVariable is placed in $anotherVariable 11: print $anotherVariable; // prints 42 assigned to $anotherVariable. A copy of the value of $aVariable is placed in $anotherVariable. Changing the value of $aVariable to 325 has no effect on the contents of $anotherVariable. The print statement demonstrates this by outputting 42 to the browser. In PHP4, you can change this behavior, forcing a reference to $aVariable to be Listing 4.3. No Listing 4.3: Assigning a Variable by Reference 1: 2: 3: 4: 5: tf assigned to $anotherVariable, rather than a copy of its contents. This is illustrated in or co m er This example initializes $aVariable, assigning the value 42 to it. $aVariable is then cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 53 6: 13: 14: We have added only a single character to the code in Listing 4.2. Placing an variable, rather than a copy of its contents, is assigned to $anotherVariable. Now any changes made to $aVariable are seen when accessing $anotherVariable. In other words, both $aVariable and $anotherVariable now point to the same value. Because this technique avoids the overhead of copying values from one variable to another, it can result in a small increase in performance. Unless your script assigns variables intensively, however, this performance gain will be barely measurable. Note References to variables were introduced with PHP4. Different types of data take up different amounts of memory and may be treated therefore demand that the programmer declare in advance which type of data a variable will contain. PHP4 is loosely typed, which means that it will calculate data it means that variables can be used flexibly, holding a string at one point and an you expect a variable to hold one data type when in fact it holds something completely different. types as data is assigned to each variable. This is a mixed blessing. On the one hand, integer at another. On the other hand, this can lead to confusion in larger scripts if No Table 4.1 shows the six data types available in PHP4. Table 4.1: Data Types Example 5 Description A number whole Type Integer tf or co m er differently when they are manipulated in a script. Some programming languages cia l, Data Types http://i-tronics.blogspot.com/ us e fo re du ca ampersand (&) in front of the $aVariable variable ensures that a reference to this tio n on ly 54 Double 3.234 A floating-point number String "hello" A collection of characters special values true or false Object See Hour 8, "Arrays" Of PHP4's six data types, we will leave arrays and objects for Hours 7 and 8. You can use PHP4's built-in function gettype() to test the type of any variable. If you place a variable between the parentheses of the function call, gettype() returns a string representing the relevant type. Listing 4.4 assigns four different data types to a single variable, testing it with gettype() each time. Note You can read more about calling functions in Hour 6, "Functions." Listing 4.4: Testing the Type of a Variable 1: 2: 3: 4: 5: 6: "); 13: $testing = 5.0; tf 8: print gettype( $testing ); // integer 9: print "
"; or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca Array See Hour 7, tio "Objects" n on ly Boolean true One of the 55 14: print gettype( $testing ); // double 15: print("
"); 16: $testing = true; 17: print gettype( $testing ); // boolean 18: print "
"; 19: ?> 20: 21: integer string double boolean strings in your scripts, they should always be surrounded by double (") or single (') includes a decimal point. A boolean can be one of two special values, true or false. Note Prior to PHP4, there was no boolean type. Although true was used, it actually resolved to the integer 1. Changing Type with settype() between the parentheses and separated by commas. Listing 4.5 converts 3.14 (a No double) to the four types that we are covering in this hour. Listing 4.5: Changing the Type of a Variable with settype() 1: 2: 3: 4: http://i-tronics.blogspot.com/ tf settype(), you must place the variable to change (and the type to change it to) or PHP provides the function settype() to change the type of a variable. To use co m er cia l, quotation marks. A double is a floating-point number. That is, a number that us without a decimal point. A string is a collection of characters. When you work with e An integer is a whole or real number. In simple terms, it can be said to be a number fo re du ca This script produces the following: tio n on ly 56 5: 6: "; // 3.14 10: settype( $undecided, string ); 11: print gettype( $undecided ); // string 12: print " -- $undecided
"; // 3.14 13: settype( $undecided, integer ); 14: print gettype( $undecided ); // integer 15: print " -- $undecided
"; // 3 16: settype( $undecided, double ); 17: print gettype( $undecided ); // double 18: print " -- $undecided
"; // 3.0 19: settype( $undecided, boolean ); 21: print " -- $undecided
"; 22: ?> 23: 24: print the value of the variable $undecided to the browser. When we convert the That's why $undecided still contains 3 after we have changed it back to a double. Finally, we convert $undecided to a boolean. Any number other than 0 becomes true No when converted to a boolean. When printing a boolean in PHP, true is represented as 1 and false as an empty string, so $undecided is printed as 1. tf or string "3.14" to an integer, any information beyond the decimal point is lost forever. co In each case, we use gettype() to confirm that the type change worked and then m er cia l, http://i-tronics.blogspot.com/ us 20: print gettype( $undecided ); // boolean // 1 e fo re du ca tio n on ly 57 Changing Type by Casting By placing the name of a data type in brackets in front of a variable, you create a copy of that variable's value converted to the data type specified. The principal leaving the original variable untouched. Listing 4.6 illustrates this. Listing 4.6: Casting a Variable 1: 2: 3: 4: 5: 6: "; // 3.14 difference between settype() and a cast is the fact that casting produces a copy, 11: $holder = ( string ) $undecided; 12: print gettype( $holder ); 13: print " -- $holder
"; 14: $holder = ( integer ) $undecided; 16: print " -- $holder
"; co 15: print gettype( $holder ); m er 17: $holder = ( double ) $undecided; 18: print gettype( $holder ); tf or No 19: print " -- $holder
"; 20: $holder = ( boolean ) $undecided; // boolean // 1 21: print gettype( $holder ); 22: print " -- $holder
"; 23: ?> cia l, // string // 3.14 // integer // 3 // double // 3.14 http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 58 24: 25: We never actually change the type of $undecided, which remains a double throughout. In fact, by casting $undecided, we create a copy that is then converted to the type we specify. This new value is then stored in the variable $holder. Because we are working with a copy of $undecided, we never discard any information from it as we did in Listing 4.5. Operators and Expressions You can now assign data to variables. You can even investigate and change the data type of a variable. A programming language isn't very useful, though, unless you can manipulate the data you can store. Operators are symbols that make it possible to use one or more values to produce a new value. A value that is operated on by an operator is referred to as an operand. NEW TERM NEW TERM An operator is a symbol or series of symbols that, when used in conjunction with values, performs an action and usually produces a new value. An operand is a value used in conjunction with an operator. There are usually two operands to one operator. Let's combine two operands with an operator to produce a new value: 4+5 4 and 5 are operands. They are operated on by the addition operator (+) to produce 9. Operators almost always sit between two operands, though you will see a few exceptions later in this hour. The combination of operands with an operator to manufacture a result is called an expression. Although most operators form the basis of expressions, an expression No need not contain an operator. In fact in PHP, an expression is defined as anything that resolves to a value. This includes integer constants such as 654, variables such as $user, and function calls such as gettype(). The expression (4 + 5), therefore is an expression that consists of two further expressions and an operator. NEW TERM An expression is any combination of functions, values, and operators that resolve to a value. As a rule of thumb, if you can use it as if it were a value, it is an expression. tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 59 Now that we have the principles out of the way, it's time to take a tour of PHP4's more common operators. The Assignment Operator consists of the single character =. The assignment operator takes the value of its right-hand operand and assigns it to its left-hand operand: $name ="matt"; The variable $name now contains the string "matt". Interestingly, this construct is changes the variable $name without producing a value, but in fact, a statement that uses the assignment operator always resolves to a copy of the value of the right operand. Thus print ( $name = "matt" ); prints the string "matt" to the browser in addition to assigning "matt" to $name. Arithmetic Operators The arithmetic operators do exactly what you would expect. Table 4.2 lists these operators. The addition operator adds the right operand to the left operand. The operator divides the left-hand operand by the right. The multiplication operator multiplies the left-hand operand by the right. The modulus operator returns the remainder of the left operand divided by the right. Table 4.2: Arithmetic Operators Operator + − subtraction operator subtracts the right-hand operand from the left. The division or co m er Name cia l, us Example 10+3 10− 3 10/3 10*3 10%3 e tf No Addition Subtraction Division Multiplication Modulus / * % http://i-tronics.blogspot.com/ fo re du ca Example Result 13 7 30 1 an expression. It might look at first glance that the assignment operator simply 3.3333333333333 tio n on ly You have met the assignment operator each time we have initialized a variable. It 60 The Concatenation Operator The concatenation operator is a single dot. Treating both operands as strings, it appends the right-hand operand to the left. So "hello"." world" returns "hello world" Regardless of the data types of the operands, they are treated as strings, and the More Assignment Operators Although there is really only one assignment operator, PHP4 provides a number of combination operators that transform the left-hand operand as well as return a Assignment operators break this rule. A combined assignment operator consists of a standard operator symbol followed by an equals sign. Combination assignment operators save you the trouble of using two operators yourself. For example, $x = 4; result. As a rule, operators use their operands without changing their values. is equivalent to $x = 4; $x = $x + 4; // $x now equals 8 There is an assignment operator for each of the arithmetic operators and one for the Table 4.3: Some Combined Assignment Operators Example $x += 5 $x − = 5 $x /= 5 Equivalent to $x = $x + 5 $x = $x − 5 $x = $x / 5 No Operator += −= /= tf concatenation operator. Table 4.3 lists some of the most common. or co m er $x += 4; // $x now equals 8 cia l, http://i-tronics.blogspot.com/ us e fo re du ca result always is a string. tio n on ly 61 * = $x *= 5 $x%=5 $x .= "test" $x = $x * 5 %= .= $x = $x % 5 $x = $x" test" Each of the examples in Table 4.3 transforms the value of $x using the value of the right-hand operand. Comparison Operators Comparison operators perform tests on their operands. They return the boolean value true if the test is successful, or false otherwise. This type of expression is useful in control structures, such as if and while statements. You will meet these in Hour 5. To test whether the value contained in $x is smaller than 5, for example, you would use the less than operator: $x < 5 contained 7, the expression would resolve to false. Table 4.4 lists the comparison operators. Table 4.4: Comparison Operators Operator m er Name cia l, us If $x contained 3, this expression would be equivalent to the value true. If $x e Returns True if Left equivalent to right Left is not equivalent to right is fo re du ca Example $x == 5 $x != 5 is $x === 5 No === tf != or co == Equivalence Non-equivalence Identical Left equivalent to right and they are the same type http://i-tronics.blogspot.com/ tio n Result false true false on ly 62 > Greater Left is than greater than right $x >4 false >= Greater equal to than or Left greater than equal right is or to $x >= 4 true than right <= Less than or equal to Left is less than equal right fo re du ca $x <= 4 or to These operators are most commonly used with integers or doubles, although the equivalence operator is also used to compare strings. Creating More Complex Test Expressions with the Logical Operators The logical operators test combinations of booleans. The or operator, for example returns true if either the left or the right operand is true. true || false would return true. The and operator only returns true if both the left and right operands are true. would return false. It's unlikely that you would use a logical operator to test boolean No constants, however. It would make more sense to test two or more expressions that resolve to a boolean. For example, ( $x > 2 ) && ( $x < 15 ) would return true if $x contained a value that is greater than 2 and smaller than 15. We include the parentheses to make the code easier to read. Table 4.5 lists the logical operators. tf or true && false co m er cia l, http://i-tronics.blogspot.com/ us e tio < Less than Left is less x<4 n true on ly false 63 Table 4.5: Logical Operators Operator Name Returns True if… || Or Left or right is true or Or Left or right is true xor Xor Left or right is true but not both && And Left right true and And Left right true ! Not The and are true && false true || true false true || false true true || false true Example Result and are operand not true Why are there two versions of both the or and the and operators? The answer lies in Automatically Incrementing and Decrementing an Integer Variable integer variable. You will usually need to do this when you are counting the iterations of a loop. You have already learned two ways of doing this. I could No increment the integer contained by $x with the addition operator $x = $x + 1; // $x is incremented or with a combined assignment operator $x += 1; // $x is incremented tf or When coding in PHP, you will often find it necessary to increment or decrement an co m er operator precedence, which you will look at later in this section. cia l, http://i-tronics.blogspot.com/ us single is e fo re du ca false true && false false ! true false tio n on ly 64 In both cases, the resultant integer is assigned to $x. Because expressions of this kind are so common, PHP provides some special operators that allow you to add or subtract the integer constant 1 from an integer variable, assigning the result to the variable itself. These are known as the post-increment and post-decrement operators. The post-increment operator consists of two plus symbols appended to a variable name. $x++; // $x is incremented increments the variable $x by one. Using two minus symbols in the same way $x− − ; // $x is decremented If you use the post-increment or post-decrement operators in conjunction with a conditional operator, the operand will only be modified after the test has been completed: $x = 3; $x++ < 4; // true incremented. In some circumstances, you might want to increment or decrement a variable in a test expression before the test is carried out. PHP provides the pre -increment and exactly the same way as the post-increment and post-decrement operators. They are written with the plus or minus symbols preceding the variable: pre-decrement operators for this purpose. On their own, these operators behave in − − $x; // $x is decremented If these operators are used as part of a test expression, the incrementation occurs before the test is carried out. No $x = 3; ++$x < 4; // false In the previous fragment, $x is incremented before it is tested against 4. The test expression returns false because 4 is not smaller than 4. tf or co ++$x; // $x is incremented m er cia l, http://i-tronics.blogspot.com/ us operator, so the test expression returns true. After this test is complete, $x is e In the previous example, $x contains 3 when it is tested against 4 with the less than fo re du ca tio n decrements the variable: on ly 65 Operator Precedence When you use an operator, the interpreter usually reads your expression from left to right. For complex expressions that use more than one operator, though, the waters can become a little murky. First, consider a simple case: 4+5 4+5 * 2 This presents a problem. Does it mean the sum of 4 and 5, which should then be multiplied by 2, giving the result 18? Does it mean 4 plus the result of 5 multiplied by 2, resolving to 14? If you were to read simply from left to right, the former would be true. In fact, PHP attaches different precedence to operators. Because the multiplication operator has higher precedence than the addition operator does, the second solution to the problem is the correct one. expression with parentheses: (4+5) * Whatever the precedence of the operators in a complex expression, it is a good idea Table 4.6 lists the operators covered in this hour in precedence order (highest first). Table 4.6: Order of Precedence for Selected Operators Operators No +− < <= => > == === != && || tf / *% or ++ − − (cast) co m er to use parentheses to make your code clearer and to save you from obscure bugs. cia l, 2 http://i-tronics.blogspot.com/ us You can force PHP to execute the addition expression before the multiplication e fo re du ca tio fragment? n There's no room for confusion, here. PHP simply adds 4 to 5. What about the next on ly 66 = += − = /= *=%= .= and xor or As you can see, or has a lower precedence than || and and has a lower precedence than &&, so you could use the lower-precedence logical operators to change the way two expressions are equivalent, but the second is much easier to read: $x and $y || $z ( $x && $y ) || $z a complex test expression is read. This is not necessarily a good idea. The following Constants Variables offer a flexible way of storing data. You can change their values and the type of data they store at any time. If, however, you want to work with a value that you do not want to alter throughout your script's execution, you can define a constant. You must use PHP's built-in function define() to create a constant. After you have done this, the constant cannot be changed. To use the define() function, you must place the name of the constant and the value you want to give it within the call's parentheses: The value you want to set can only be a number or a string. By convention, the constant name only; no dollar symbol is required. Listing 4.7 defines and accesses Listing 4.7: Defining a Constant No tf 1: 2: 3: 4: 5: 6: 10: 11: Notice that we used the concatenation operator to append the value held by our distinguishing between a constant and a string within quotation marks. Predefined Constants PHP automatically provides some built-in constants for you. __FILE__, for example, returns the name of the file currently being read by the interpreter. __LINE__ returns the line number of the file. These constants are useful for generating error messages. You can also find out which version of PHP is interpreting the script with PHP_VERSION. This can be useful if you want to limit a script to run on a particular Summary learned about variables and how to assign to them using the assignment operator. You learned about dynamic or "variable" variables. You also learned how to assign to variables by reference rather than by value. You were introduced to operators and learned how to combine some of the most common of these into expressions. No Q&A Q Why can it be useful to know the type of data a variable holds? A Often the data type of a variable constrains what you can do with it. You may want to make sure that a variable contains an integer or a double before using it in a mathematical calculation, for example. tf or Finally, you learned how to define and access constants. co m er In this hour, you covered some of the basic features of the PHP language. You cia l, http://i-tronics.blogspot.com/ us PHP release. e fo re du ca tio n constant to the string "Welcome". This is because the interpreter has no way of on ly 68 You explore situations of this kind a little further in Hour 16, "Working with Data." Q Should I obey any conventions when naming variables? A Your goal should always be to make your code both easy to read and understand. A variable such as $ab123245 tells you nothing about its role in your script and invites typos. Keep your variable names short and descriptive. A variable named $f is unlikely to mean much to you when you return to your code after a month or so. A variable named $filename, on the other hand, should make more sense. Q Should I learn the operator precedence table? A There is no reason why you shouldn't, but I would save the effort for more useful tasks. By using parentheses in your expressions, you can make your code easy to read at the same time as defining your own order of precedence. Workshop The Workshop provides quiz questions to help you solidify your understanding of the material covered. Try to understand the quiz answers before continuing to the next hour's lesson. Quiz answers are provided in Appendix A. Quiz Which of the following variable names is not valid? $a_value_submitted_by_a_user $666666xyz $xyz666666 No $the first $file-name How could you use the string variable created in the assignment expression $my_var = "dynamic"; to create a "variable" variable, assigning the integer 4 to it. How might you access this new variable? tf $_____counter____ or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 69 What will the following statement output? print gettype("4"); What will be the output from the following code fragment? $test_val = 5.4566; settype( $test_val, "integer" ); print $test_val; Which of the following statements does not contain an expression? 4; gettype(44); 5/12; Which of the statements in question 5 contains an operator? What value will the following expression return? 5<2 What data type will the returned value be? Activities Create a script that contains at least five different variables. Populate them with the browser. first value is Assign values to two variables. Use comparison operators to test whether the The same as the second Less than the second Less than or equal to the second Print the result of each test to the browser. Change the values assigned to your test variables and run the script again. No tf or co Greater than the second m er cia l, values of different data types and use the gettype() function to print each type to http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 70 Hour 5: Going with the Flow Overview The scripts created in the last hour flow only in a single direction. The same leave much room for flexibility. statements are executed in the same order every time a script is run. This does not You now will look at some structures that enable your scripts to adapt to How to use the if statement to execute code only if a test expression evaluates to true statement evaluates to false a test expression How to execute alternative blocks of code when the test expression of an if How to use the switch statement to execute code based on the value returned by How to repeat execution of code using a while statement How to break out of loops Most scripts evaluate conditions and change their behavior accordingly. The facility according to circumstances. Like most programming languages, PHP4 allows you to The if Statement No The if statement evaluates an expression between parentheses. If this expression results in a true value, a block of code is executed. Otherwise, the block is skipped entirely. This enables scripts to make decisions based on any number of factors. if ( expression ) { tf or do this with an if statement. co to make decisions makes your PHP pages dynamic, capable of changing their output m er Switching Flow cia l, How to nest one loop within another http://i-tronics.blogspot.com/ us How to use for statements to make neater loops e fo re du ca circumstances. In this hour, you will learn tio n on ly 71 // code to execute if the expression evaluates to true } Listing 5.1 executes a block of code only if a variable contains the string "happy". Listing 5.1: An if Statement 2: 3: 4: 5: 6: 13: 14: { print "Hooray, I'm in a good mood"; } You use the comparison operator == to compare the variable $mood with the string "happy". If they match, the expression evaluates to true, and the code block below example, this is only necessary if the block contains more than one line. The the if statement is executed. Although the code block is wrapped in braces in the following fragment, therefore, would be acceptable: if ( $mood == "happy" ) No If you change the value of $mood to "sad" and run the script, the expression in the if statement evaluates to false, and the code block is skipped. The script remains sulkily silent. tf or print "Hooray, I'm in a good mood"; co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 1: 72 Using the else Clause with the if Statement When working with the if statement, you will often want to define an alternative block of code that should be executed if the expression you are testing evaluates to of code: if ( expression ) { // code to execute if the expression evaluates to true } else { // code to execute in all other cases } false. You can do this by adding else to the if statement followed by a further block executed if $mood is not equivalent to "happy". Listing 5.2: An if Statement That Uses else 1: 2: 3: 4: 5: 6: 17: 18: print "Not happy but $mood"; } $mood contains the string "sad", which is not equivalent to "happy", so the code is skipped. The block of code after else, therefore, is executed, and the message "Not happy but sad" is printed to the browser. Using the else clause with the if statement allows scripts to make sophisticated decisions, but you currently are limited to an either -or branch. PHP4 allows you to evaluate multiple expressions in a cascade. Using the elseif Clause with the if Statement default block of code: if ( expression ) { } { No else If the first expression does not evaluate to true, then the first block of code is ignored. The elseif clause then causes another expression to be evaluated. Once tf // and this one evaluates to true { // code to execute in all other cases } or // code to execute if the previous expression failed co elseif ( another expression ) m er // code to execute if the expression evaluates to true cia l, http://i-tronics.blogspot.com/ us You can use an if-elseif-else construct to test multiple expressions before offering a e fo re du ca tio n expression in the if statement evaluates to false. This means that the first block of on ly 74 again, if this expression evaluates to true, then the second block of code is executed. Otherwise, the block of code associated with the else clause is executed. You can include as many elseif clauses as you want, and if you don't need a default action, you can omit the else clause. Listing 5.3 adds an elseif clause to the previous example. 1: 2: 3: 4: 5: 6: 21: 22: tf or { print "Neither happy nor sad but $mood"; } co m er cia l, 11: } http://i-tronics.blogspot.com/ us e print "Hooray, I'm in a good mood"; fo re du ca tio n on ly Listing 5.3: An if Statement That Uses else and elseif 75 Once again, $mood holds a string, "sad". This is not equivalent to "happy", so the first block is ignored. The elseif clause tests for equivalence between the contents of $mood and "sad", which evaluates to true. This block of code is therefore executed. The switch Statement The switch statement is an alternative way of changing program flow according to the evaluation of an expression. There are some key differences between the switch different code according to the result of that expression, as long as the expression evaluates to a simple type (a number, a string, or a boolean). The result of an expression evaluated as part of an if statement is read as either true or false. The expression of a switch statement yields a result that is tested against any number of values. switch ( expression ) { case result1: // execute this if expression results in result1 case result2: break; default: No The switch statement's expression is often simply a variable. Within the switch tests a value against the result of the switch statement's expression. If these are statement ends execution of the switch statement altogether. If this is left out, the next case statement's expression is evaluated. If the optional default statement is reached, its code is executed. statement's block of code, you find a number of case statements. Each of these equivalent, then the code after the case statement is executed. The break tf or } co // execute this if no break statement // has been encountered hitherto m er // execute this if expression results in result2 cia l, break; http://i-tronics.blogspot.com/ us e fo re du ca tio evaluate multiple expressions. switch evaluates only one expression, executing n and if statements. Using the if statement in conjunction with elseif, you may on ly 76 Caution Don't forget to include a break statement at the end of any code that will be executed as part of a case statement. Without break, the program flow will continue to the next case statement and ultimately to the default statement. In most cases, this will not be the behavior that you will be expecting. statement. Listing 5.4: A switch Statement 1: 2: 3: 4: 5: 6: 20: 21: Once again, the $mood variable is initialized to "sad". The switch statement uses this variable as its expression. The first case statement tests for equivalence http://i-tronics.blogspot.com/ tf or } co break; print "Neither happy nor sad but $mood"; m er cia l, us e fo re du ca tio n on ly Listing 5.4 re-creates the functionality of the if statement example, using the switch 77 between "happy" and the value of $mood. There is no match, so script execution moves on to the second case statement. The string "sad" is equivalent to the value of $mood, so this block of code is executed. The break statement ends the process. Using the ? Operator The ? or ternary operator is similar to the if statement but returns a value derived from one of two expressions separated by a colon. Which expression is used to generate the value returned depends on the result of a test expression: If the test expression evaluates to true, the result of the second expression is returned; otherwise, the value of the third expression is returned. Listing 5.5 uses the ternary operator to set the value of a variable according to the value of $mood. Listing 5.5: Using the ? Operator 1: 2: 3: 4: 5: 6: 11: No 12: $mood is set to "sad". $mood is tested for equivalence to the string "happy". Because this test returns false, the result of the third of the three expressions is returned. tf or co $mood"; m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca _false; tio ( expression )?returned_if_expression_is_true:returned_if_expression_is n on ly 78 The ternary operator can be difficult to read but is useful if you are dealing with only two alternatives and like to write compact code. Loops Scripts can also decide how many times to execute a block of code. Loop statements are designed to enable you to achieve repetitive tasks. Almost without exception, a exit the loop. The while Statement loop continues to operate until a condition is achieved, or you explicitly choose to The while statement looks similar in structure to a basic if statement: while ( expression ) { // do something } executed over and over again. Within the block, you usually change something that affects the while statement's expression; otherwise, your loop continues indefinitely. Listing 5.6: A while Statement 1: 2: Listing 5.6 creates a while loop that calculates and prints multiples of two. No 10: tf 4: 5: 6: "; or 3: co m er cia l, As long as a while statement's expression evaluates to true, the code block is http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly So far you've looked at decisions that a script can make about what code to execute. 79 11: 12: 13: ?> 14: 15: $counter++; } In this example, we initialize a variable $counter. The while statement tests the value contained by $counter is multiplied by two, and the result is printed to the browser. Then $counter is incremented. This last stage is extremely important. If you were to forget to change $counter, the while expression would never resolve to false, and the loop would never end. The do..while Statement truth test and not after it: do { // code to be executed } while ( expression ); semicolon. This statement might be useful if you want the code block to be executed at least statement. The code block is executed a minimum of one time. Listing 5.7: The do...while Statement 1: 2: 3: 4: No tf once even if the while expression evaluates to false. Listing 5.7 creates a do...while or co Note The test expression of a do...while statement should always end with a m er cia l, http://i-tronics.blogspot.com/ us essential difference between the two is that the code block is executed before the e A do...while statement looks a little like a while statement turned on its head. The fo re du ca tio equal to 12, the loop continues to run. Within the while statement's code block, the n $counter variable. As long as the integer contained by $counter is smaller than or on ly 80 5: 6: 15: 16: { print "Execution number: $num
\n"; $num++; } while ( $num > 200 && $num < 400 ); The do...while statement tests whether the variable $num contains a value that is greater than 200 and smaller than 400. We have initialized $num to 1 so this expression returns false. Nonetheless, the code block is executed before the expression is evaluated, so the statement will print a single line to the browser. The for Statement You cannot achieve anything with a for statement that you cannot do with a while statement. On the other hand, the for statement is often a neater and safer way of statement. The while statement then tested the variable in its expression. The variable was incremented within the code block. The for statement allows you to achieve this on a single line. This allows for more compact code and makes it less loop. likely that you forget to increment a counter variable, thereby creating an infinite achieving the same effect. Earlier, Listing 5.6 initialized a variable outside the while No for ( variable assignment; test expression; variable increment ) { // code to be executed } tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 81 Each of the expressions within the parentheses of the for statement is separated by semicolons. Usually, the first expression initializes a counter variable, the second expression is the test condition for the loop, and the third expression increments the counter. Listing 5.8 shows a for statement that re-creates the example in Listing 5.6, which multiplies 12 numbers by 2. Listing 5.8: Using the for Statement 1: 2: 3: 4: 5: 6: 12: 13: { print "$counter times 2 is ".($counter*2)."
"; } makes the code more compact. Because $counter is initialized and incremented at the top of the statement, the logic of the loop is clear at a glance. Within the for statement's parentheses, the first expression initializes the $counter variable and sets it to 1. The test expression checks that $counter contains a value that is less than or equal to 12. The final expression increments the $counter variable. When program flow reaches the for loop, the $counter variable is initialized, and the No test expression is evaluated. If the expression evaluates to true, the code block is executed. The $counter variable is then incremented and the test expression evaluated again. This process continues until the test expression evaluates to false. tf or co m er The results of Listings 5.6 and 5.8 are exactly the same. The for statement, though, cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 82 Breaking Out of Loops with the break Statement Both while and for statements incorporate a built-in test expression with which you can end a loop. The break statement, though, enables you to break out of a loop creates a simple for statement that divides a large number by a variable that is incremented, printing the result to the screen. Listing 5.9: A for Loop That Divides 4000 by Ten Incremental Numbers according to additional tests. This can provide a safeguard against error. Listing 5.9 3: 4: 5: 6: $temp = 4000/$counter; } 13: 14: This example initializes the variable $counter to 1. The for statement's test block, 4000 is divided by $counter, printing the result to the browser. This seems straightforward enough. What, though, if the value you place in $counter comes from user input? The value could be a minus number, or even a string. Let's take the first instance. Changing the initial value of $counter from 1 to − 4 causes 4000 to be divided by zero as the code block is executed for the fifth time, which is not advisable. Listing 5.10 guards against this by breaking out of the loop if the $counter variable contains zero. No tf expression checks that $counter is smaller than or equal to 10. Within the code or co m er cia l, print "4000 divided by $counter is... $temp
"; http://i-tronics.blogspot.com/ us 8: { e fo re du ca 2: tio 1: n on ly 83 Listing 5.10: Using the break Statement 1: 2: 3: 4: 5: 6: { if ( $counter == 0 ) break; $temp = 4000/$counter; print "4000 divided by $counter is... $temp
"; 16: 17: Note Dividing a number by zero does not cause a fatal error in PHP4. Instead, a warning is generated and execution continues. Use an if statement to test the value of $counter. If it is equivalent to zero, the break continues after the while statement. Notice that we initialized the $counter variable outside the for statement's parentheses to simulate a situation in which the value of $counter is set according to form input or a database look up. Tip You can omit any of the expressions of a for statement, but you must remember to retain the semicolons. No tf or statement immediately halts execution of the code block, and program flow co m er cia l, http://i-tronics.blogspot.com/ us } e fo re du ca 8: for ( ; $counter <= 10; $counter++ ) tio n on ly 84 Skipping an Iteration with the continue Statement The continue statement ends execution of the current iteration but doesn't cause the loop as a whole to end. Instead, the next iteration is immediately begun. Using in Listing 5.11, you can avoid a divide by zero error without ending the loop completely. Listing 5.11: Using the continue Statement 1: 2: 3: the break statement in Listing 5.10 was a little drastic. With the continue statement 4: 5: 6: if ( $counter == 0 ) continue; $temp = 4000/$counter; } No 17: We have swapped the break statement for a continue statement. If the $counter variable is equivalent to zero, the iteration is skipped, and the next one immediately is started. Caution The break and continue statements can make code more difficult tf 16: or co print "4000 divided by $counter is... $temp
"; m er cia l, 9: { http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 85 to read. Because they often add layers of complexity to the logic of the loop statements that contain them, they can lead to obscure bugs. They are best used sparingly. Nesting Loops Loop statements can contain other loop statements. This combination is particularly for statements to print a multiplication table to the browser. Listing 5.12: Nesting Two for Loops 1: 2: 3: 4: 5: 6: \n"; 8: for ( $y=1; $y<=12; $y++ ) 9: 10: { useful when working with dynamically created HTML tables. Listing 5.12 uses two print "\n"; 11: 12: 13: 14: 15: 16: for ( $x=1; $x<=12; $x++ ) { tf No 17: 18: 19: print ""; 20: ?> 21: or print "\n"; } co print "\t"; print ($x *$y); print "\n"; } m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 86 22: The outer for statement initializes a variable called $y, setting its starting value to 1. It defines an expression that tests that $y is smaller or equal to 12 and defines the increment for $y. For each iteration, the code block prints a TR (table row) HTML called $x and defines expressions along the same lines as for the outer loop. For each iteration, the inner loop prints a TD (table cell) element to the browser, as well table. as the result of $x multiplied by $y. The result is a neatly formatted multiplication element and defines another for statement. This inner loop initializes a variable Summary In this hour, you learned about control structures and the ways in which they can help to make your scripts flexible and dynamic. Most of these structures will reappear regularly throughout the rest of the book. change flow according to multiple equivalence tests on the result of an expression. learned how to use break and continue to prematurely end the execution of a loop or to skip an iteration. Finally, you learned how to nest one loop within another and saw a typical use for this structure. No or an empty string will be converted to false for the purposes of the test. All other values will evaluate to true. Q Must I always surround a code block in a control statement with brackets? A If the code you want executed as part of a control structure consists of only a single line, you can omit the brackets. tf A Ultimately, yes, but in the context of a test expression zero, an undefined variable, or Q Must a control structure's test expression result in a boolean value? co Q&A m er cia l, You learned about loops, in particular, the while and for statements, and you http://i-tronics.blogspot.com/ us with the elseif and else clauses. You learned how to use the switch statement to e You learned how to define an if statement and how to provide for alternative actions fo re du ca tio n on ly 87 Q Does this hour cover every kind of loop there is? A In Hour 7, "Arrays," you encounter the foreach statement, which enables you to loop through every element in an array. No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 88 Hour 6: Functions Overview Functions are the heart of a well-organized script, making code easy to read and reuse. No large project would be manageable without them. ways in which they can save you from repetitive work. In this hour, you will learn How to pass values to functions and receive values in return How to access global variables from within a function How to give a function a "memory" How to pass data to functions by reference How to call a function dynamically using a string stored in a variable feed it and works with them to achieve a purpose or to produce a product. A function the browser, for example) or returns a new value, possibly both. If you needed to bake a single cake, you would probably do it yourself. If you cake-baking machine. Similarly, when deciding whether to create a function, the most important factor to consider is the extent to which it can save you from repetition. A function, then, is a self-contained block of code that can be called by your scripts. When called, the function's code is executed. You can pass values to functions, the calling code. NEW TERM A function is a block of code that is not immediately executed but can be called by your scripts when needed. Functions can be built-in or user-defined. They can require information to be passed to them and usually return a value. which they will then work with. When finished, a function can pass a value back to needed to bake thousands of cakes, you would probably build or acquire a No Calling Functions Functions come in two flavors— those built in to the language and those you define http://i-tronics.blogspot.com/ tf or co m er cia l, accepts values from you, processes them, and then performs an action (printing to us You can think of a function as a machine. A machine takes the raw materials you e What Is a Function? fo re du ca How to define and call functions tio n Throughout this hour, we will investigate functions and demonstrate some of the on ly 89 yourself. PHP4 has hundreds of built-in functions. The very first script in this book consisted of a single function call: print("Hello Web"); Note print() is not a typical function in that it does not require parentheses in order to run successfully. print(("Hello Web"); and print "Hello Web"; parentheses, whether or not they accept arguments. are equally valid. This is an exception. All other functions require In this example, we called the print() function, passing it the string "Hello Web". The of the function name, print in this case, followed by parentheses. If you want to pass information to the function, you place it between these parentheses. A piec e of information passed to a function in this way is called an argument. Some functions require that more than one argument be passed to them. Arguments in these cases must be separated by commas: some_function( $an_argument, $another_argument ); successful. print() returns a boolean, therefore. absolute value of that number. Let's try it out in Listing 6.1. Listing 6.1: Calling the Built in abs() Function 2: 4: 5: 6: 3: No 10: // prints "321" 11: ?> 12: 13: tf 7: $num = − 321; 8: $newnum = abs( $num ); 9: print $newnum; or co m er cia l, The abs() function, for example, requires a signed numeric value and returns the http://i-tronics.blogspot.com/ us back when they've completed their task, if only to tell whether their mission was e print() is typical in that it returns a value. Most functions give you some information fo re du ca function then went about the business of writing the string. A function call consists tio n on ly 90 In this example, we assign the value − 321 to a variable $num. We then pass that variable to the abs() function, which made the necessary calculation and returned a new value. We assign this to the variable $newnum and print the result. In fact, we could have dispensed with temporary variables altogether, passing our number straight to abs(), and directly printing the result: print( abs( − 321 ) ); The rules for calling user-defined functions are almost exactly the same. NEW TERM An argument is a value passed to a function. Arguments are included within the parentheses of a function call. User-defined functions of the function definition. These arguments then become available to Defining a Function You can define a function using the function statement: function some_function( $argument1, $argument2 ) { // function code here } parentheses. If your function is us The name of the function follows the function statement and precedes a set of to require arguments, you must place comma-separated variable names within the parentheses. These variables will be filled by the values passed to your function. If your function requires no arguments, you must nevertheless supply the parentheses. Listing 6.2: Declaring a Function 1: 2: Listing 6.2 declares a function. 3: 4: 5: 6: No 11: bighello(); tf 7: function bighello() { print "

HELLO!

"; } or co m er cia l, http://i-tronics.blogspot.com/ e fo re du ca the function as local variables. tio n include comma-separated argument names within the parentheses on ly 91 13: 14: The script in Listing 6.2 will simply output the string "HELLO" wrapped in an HTML

element. We declare a function bighello() that requires no arguments. Because of this, we leave the parentheses empty. bighello() is a working function but not terribly useful. Listing 6.3 creates a function that requires an argument and actually does something helpful with it. Listing 6.3: Declaring a Function That Requires Arguments 1: 2: 3: 4: 5: 6: \n"); } 12: printBR("This is a new line"); 14: ?> 15: 16: No Figure 6.1: A function that prints a string with an appended
tag. tf or co m er cia l, 13: printBR("This is yet another line"); http://i-tronics.blogspot.com/ us 11: printBR("This is a line"); e fo re du ca tio n on ly 92 You can see the output from the script in Listing 6.3 in Figure 6.1. The printBR() function expects a string, so we place the variable name $txt between the parentheses when we declare the function. Whatever is passed to printBR() is stored in $txt. Within the body of the function, we print the $txt variable, appending a
element and a newline character to it. Now when we want to write a line to the browser, we can call printBR() instead of the built-in print(), saving us the bother of typing the
element. Returning Values from User-Defined Functions or object. return stops the execution of the function and sends the value back to the Listing 6.4 creates a function that returns the sum of two numbers. Listing 6.4: A Function That Returns a Value 1: 2: 3: 4: 5: 6: 15: 16: No two numeric arguments (3 and 5 in this case). These are stored in the variables $firstnum and $secondnum. Predictably, addNums() adds the numbers contained in these variables together and stores the result in a variable called $result. Once again, we can dispense with a stage in this code, doing away with the temporary $result variable altogether: function addNums( $firstnum, $secondnum ) { tf The script in Listing 6.4 will print the number '8'. addNums() should be called with or co m er 12: print addNums(3,5); cia l, http://i-tronics.blogspot.com/ us e fo re du ca calling code. tio n A function can return a value using the return statement in conjunction with a value on ly 93 return ( $firstnum + $secondnum ); } The return statement can return a value, an object, or even nothing at all. How a value passed by return is arrived at can vary. The value could be hard-coded: return 4; It could be the result of an expression: return ( $a/$b ); It could be the value returned by yet another function call: return ( another_function( $an_argument ) ); variables exactly as you would the function name itself. Listing 6.5 creates a simple example of this. 1: 2: 3: 4: 5: 6: "; 11: $function_holder = "sayHello"; 12: $function_holder(); 13: ?> 14: 15: No A string identical to the name of the sayHello() function is assigned to the $function_holder variable. Once this is done, we can use this variable in conjunction Why would we want to do this? In the example, we simply made more work for ourselves by assigning the string "sayHello" to $function_holder. Dynamic function calls are useful when you want to alter program flow according to changing circumstances. We might want our script to behave differently according to a with parentheses to call the sayHello() function. tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca It is possible to assign function names as strings to variables and then treat these tio Dynamic Function Calls n on ly 94 parameter set in a URL's query string, for example. We could extract the value of this parameter and use it to call one of a number of functions. PHP's built-in functions also make use of this feature. The array_walk() function, for example uses a string to call a function for every element in an array. You can see an example of array walk() in action in Hour 16. Variable Scope projects, this can save you from accidentally overwriting the contents of a variable when you declare two variables of the same name in separate functions. Listing 6.6 creates a variable within a function and then attempts to print it outside the function. Unavailable Outside the Function 1: 2: 3: 4: 5: 6: 13: 14: tf 11: print "test variable: $testvariable
"; or } co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio it will not be available outside the function or within other functions. In larger n A variable declared within a function remains local to that function. In other words, on ly 95 You can see the output of the script in Listing 6.6 in Figure 6.2. The value of the variable $testvariable is not printed. This is because no such variable exists outside the test() function. Note that attempting to access a nonexistent variable does not cause an error. Similarly, a variable declared outside a function will not automatically be available Accessing Variables with the global Statement From within a function, it is not possible by default to access a variable that has set or access a local variable only. Let's put this to the test in Listing 6.7. Listing 6.7: Variables Defined Outside Functions Are Inaccessible from Within a Function by Default 1: 2: No tf 3: 4: 5: 6: "; } 12: meaningOfLife(); 13: ?> 14: 15: You can see the output from the script in Listing 6.7 in Figure 6.3. As you might empty when the function attempts to print it. On the whole, this is a good thing. We're saved from potential clashes between identically named variables, and a function can always demand an argument if it needs information about the outside world. Occasionally, however, you may want to access an important global variable from within a function without passing it in as an argument. This is where the global statement comes into its own. Listing 6.8 uses global to restore order to the universe. No Listing 6.8: Accessing Global Variables with the global Statement 1: 2: 3: 4: 5: tf Figure 6.3: Attempting to print a global variable from within a function. or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca expect, the meaningOfLife() function has no access to the $life variable; $life is tio n on ly 97 6: "; } 14: ?> 15: 16: You can see the output from the script in Listing 6.8 in Figure 6.4. By placing global in front of the $life variable when we declare it in the meaning_of_life() function, we make it refer to the global $life variable declared outside the function. particular global variable. Be careful, though. If we manipulate the contents of the variable within the function, $life will be changed for the script as a whole. Usually, an argument is a copy of beyond the function block. Changing a global variable within a function on the other hand changes the original and not a copy. Use the global statement sparingly. whatever value is passed by the calling code; changing it in a function has no effect No Figure 6.4: Successfully accessing a global variable from within a function using tf or co m er cia l, http://i-tronics.blogspot.com/ us You will need to use the global statement for every function that wishes to access a e fo re du ca tio n 13: meaningOfLife(); on ly 98 the global keyword. Saving State Between Function Calls with the static Statement Variables within functions have a short but happy life on the whole. They come into being when the is finished. Once again, this is as it should be. It is usually best to build a script as a series of self-contained blocks, each with as little knowledge of others as possible. Occasionally, however, you may want to give a function a rudimentary memory. been called. Why? In our examples, the function is designed to create numbered We could, of course use our newfound knowledge of the this. We have a crack at this in Listing 6.9. Variable Between Function Calls 1: 2: 3: 4: 5: 6: $num_of_calls. $txt

"; No 15: print("We build a fine range of widgets

"); 17: print("Finest in the world

"); 18: ?> 19: 20: 16: andAnotherThing("Doodads"); tf 14: andAnotherThing("Widgets"); or } co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca headings in a script that dynamically builds online documentation. global statement to do tio n Let's assume that we want a function to keep track of the number of times it has on ly andAnotherThing() function is called and die when execution 99 function has been called. This does the job. We declare a variable, andAnotherThing(). We make this variable available to the function with the global statement. You can see the output of Listing 6.9 in Figure 6.5. Every time andAnotherThing() is called, $num_of_calls is incremented. We can then print out a heading complete with a heading number. fo re du ca Figure 6.5: Using the global statement to keep track of the number of times a $num_of_calls, outside the function tio we need to look out for the global variables that they manipulate. function. On the other hand, the function "remembers" the value of the variable static statement. Listing 6.10: Using the static Statement to Remember the Value of a Variable Between Function Calls 1: 2: No 10: tf 3: 4: 5: 6: $num_of_calls. $txt"; } 13: andAnotherThing("Widgets"); 14: print("We build a fine range of widgets

"); 15: andAnotherThing("Doodads"); 16: print("Finest in the world

"); 17: ?> 18: 19: is ignored when the function is called a second time. Instead, the previous value of $num_of_calls is remembered. We can now paste the andAnotherThing() function into other scripts without worrying about global variables. Although the output of Listing 6.10 is exactly the same as that for Listing 6.9, we have made the code more elegant. You've already seen how to pass arguments to functions, but there's more to cover yet. In this section, you'll look at a technique for giving your arguments default values and explore a method of passing references to variables rather than copies of their values to your functions. Setting Default Values for Arguments PHP gives you a nifty feature to help build flexible functions. Until now, we've said that some functions "demand" one or more arguments. By making some arguments No Listing 6.11 creates a useful little function that wraps a string in an HTML font element. We want to give the user of the function the chance to change the font element's size attribute, so we demand a $size argument in addition to the string. Listing 6.11: A Function Requiring Two Arguments 1: 2: tf optional, you can render your functions a little less autocratic. or co m er cia l, http://i-tronics.blogspot.com/ us More About Arguments e fo re du ca andAnotherThing() has become entirely self-contained. When we declare the $num_of_calls variable, we assign an initial value to it. This initial assignment tio n on ly 101 3: 4: 5: 6: $txt";10: } 11: fontWrap("A heading
",5); 12: fontWrap("some body text
",3); 13: fontWrap("some more body text
",3); 14: fontWrap("yet more body text
",3); 15: ?> 16: 17: Figure 6.6: A function that formats and outputs strings. No You can see the output from the script in Listing 6.11 in Figure 6.6. Useful though this function is, we really only need to change the font size occasionally. Most of the time we default to 3. By assigning a value to an argument variable within the function definition's parentheses, we can make the $size argument optional. If the function call doesn't define an argument for this, the value we have assigned to the tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 102 argument is used instead. Listing 6.12 uses this technique to make the $size argument optional. Listing 6.12: A Function with an Optional Argument 1: 2: 3: 4: 5: 6: $txt"; 10: } 11: fontWrap("A heading
",5); 12: fontWrap("some body text
"); 13: fontWrap("some more body text
"); 14: fontWrap("yet more body text
"); 16: 17: set the size attribute of the font element. When we omit this argument, the default value of 3 is used instead. You can create as many optional arguments as you want, but when you've given an argument a default value, all subsequent arguments should also be given defaults. No Passing References to Variables to Functions When you pass arguments to functions they are stored as copies in parameter variables. Any changes made to these variables in the body of the function are local to that function and are not reflected beyond it. This is illustrated in Listing 6.13. Listing 6.13: Passing an Argument to a Function by Value tf or co When the fontWrap() function is called with a second argument, this value is used to m er cia l, 15: ?> http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 103 1: 2: 3: 4: 5: 6: 15: 16: The addFive() function accepts a single numeric value and adds 5 to it. It returns nothing. We assign a value to a variable $orignum and then pass this variable to Although we increment $num by 5, this has no effect on the value of $orignum. When we print $orignum, we find that its value is still 10. By default, variables of the variables are made. It is possible to pass arguments to functions by reference. This means that a variable's value. Any changes made to an argument in these cases will change the value of the original variable. You can pass an argument by reference by adding an ampersand to the variable name in either the function call or the function definition. passed to functions are passed by value. In other words, local copies of the values addFive(). A copy of the contents of $orignum is stored in the variable $num. No Listings 6.14 and 6.15 show each technique in turn. Listing 6.14: Using a Function Call to Pass an Argument to a Function by Reference 1: tf reference to the variable is manipulated by the function rather than a copy of the or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 104 2: 3: 4: 5: 6: 15: 16: Listing 6.15: Using a Function Definition to Pass an Argument to a Function 1: 2: 3: 4: 5: 6: 15: 16: In this way, you can be sure that the function behaves consistently from call to call. In this hour, you learned about functions and how to deploy them. You learned how to define and pass arguments to a function. You learned how to use the global and static statements. You learned how to pass references to functions and how to create default values for function arguments. Q&A associative array called $GLOBALS. To access a global variable called $test within a function, you could reference it as $GLOBALS[test]. You can learn more about associative arrays in the next hour. You can also change global variables from within a function if it has been passed in Q Can you include a function call within a string, as you can with a variable? A No. You must call functions outside quotation marks. No Workshop The Workshop provides quiz questions to help you solidify your understanding of the material covered. Try to understand the quiz answers before continuing to the next hour's lesson. Quiz answers are provided in Appendix A. tf or co by reference. m er cia l, A You can also access global variables anywhere in your scripts with a built-in http://i-tronics.blogspot.com/ us access and change global variables? e Q Apart from the global keyword, is there any way that a function can fo re du ca tio n Summary on ly On the whole, it makes more sense to add the ampersand to the function definition. 106 Quiz True or False: If a function doesn't require an argument, you can omit the parentheses in the function call. How do you return a value from a function? What would the following code fragment print to the browser? $number = 50; function tenTimes() { $number = $number } tenTimes(); print $number; * What would the following code fragment print to the browser? $number = 50; function tenTimes() { global $number; $number = $number tenTimes(); print $number; What would the following code fragment print to the browser? No tf function tenTimes( $n ) { or $number = 50; tenTimes( $number ); print $number; co $n = $n } m er } * 10; cia l, http://i-tronics.blogspot.com/ us * 10; e fo re du ca 10; tio n on ly 107 What would the following code fragment print to the browser? $number = 50; function tenTimes( &$n ) { $n = $n } tenTimes( $number ); print $number; Activity * 10; Create a function that accepts four string variables and returns a string that contains an HTML table element, enclosing each of the variables in its own cell. No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 108 Hour 7: Arrays Overview Arrays, and the tools to manipulate them, greatly enhance the scope and flexibility of PHP4 scripts. After you've mastered arrays, you will be able to store and organize complex data structures. This hour introduces arrays and some of the functions that help you work with them. What arrays are and how to create them How to access data from and about arrays How to access and sort the data contained in arrays What Is an Array? You already know that a variable is a "bucket" in which you can temporarily store a outputs different information every time it is run. Unfortunately, you can only store one value at a time in a variable. Arrays are special variables that allow you to in the same variable. Each value is indexed within the array by a number or a string. If a variable is a bucket, you can think of an array as a filing cabinet— a single NEW TERM container that can store many discrete items. overcome this limitation. An array allows you to store as many values as you want Of course, if you have five values to store, you could always define five variables. So, why use an array rather than a variable? First, an array is flexible. It can store two an array allows you to work easily with all its items. You can loop through each item or pull one out at random. You can sort items numerically, alphabetically, or even according to a system of your own. Each item in an array is commonly referred to as an element. Each element can be accessed directly via its index. An index to an array element can be either a number or a string. By default, array elements are indexed by number starting at zero. It's important to remember, therefore, that the index of the last element of a numerically indexed http://i-tronics.blogspot.com/ No tf values or two hundred values without the need to define further variables. Second, or co m er An array is a list variable. That is, a variable that contains multiple elements indexed by numbers or strings. It enables you to store, order, and access many values under one name. cia l, us e value. By using variables, you can create a script that stores, processes, and fo re du ca In this hour, you will learn tio n on ly 109 array is always one less than the number of elements the array contains. For example, Table 7.1 shows the elements in an array called users. Notice that the third element has an index of 2. Table 7.1: The Elements in the users Array Index Number 0 1 2 3 Bert Sharon Betty Harry Value Which First Second Third Fourth and values. PHP4 provides tools to access and manipulate arrays indexed by both name and number. Some of these are covered in this hour, and others will be covered in Hour 16, "Working with Data." By default, arrays are lists of values indexed by number. Values can be assigned to an array in two ways: with the array() function or directly using the array identifier []. You'll meet both of these in the next two sections. Defining Arrays with the array() Function one time. Let's define an array called $users and assign four strings to it: No print "$users[2]"; This would return the string "Sharon". The index of an array element is placed between square brackets directly after the array name. You can use this notation either to set or retrieve a value. Remember that arrays are indexed from zero by default, so the index of any element always is one less than the element's place in the list. tf You can now access the third element in the $user array by using the index "2": or $users = array ("Bert", "Sharon", "Betty", "Harry" ); co The array() function is useful when you want to assign multiple values to an array at m er cia l, http://i-tronics.blogspot.com/ us e Creating Arrays fo re du ca Indexing arrays by string can be useful in cases where you need to store both names tio n on ly Element? 110 Defining or Adding to Arrays with the Array Identifier You can create a new array (or add to an existing one) by using the array identifier in conjunction with the array name. The array identifier is a set of square brackets with no index number or name inside it. Let's re-create our $users array in this way: $users[ ] = " Bert"; $users[ ] = " Sharon"; $users[ ] = " Betty"; $users[ ] = " Harry"; Notice that we didn't need to place any numbers between the square brackets. PHP4 automatically takes care of the index number, which saves you from havi ng to work out which is the next available slot. We could have added numbers if we wanted, and the result would have been exactly the same. It's not advisable to do this, though. Take a look at the following code: $users[0] = " Bert"; $users[200] = "Sharon"; The array has only two elements, but the index of the final element is 200. PHP4 will to access elements in the array. In addition to creating arrays, you can use the array identifier to add new values onto the end of an existing array. In the following code, we define an array with the array() function and use the array identifier to add a new element: $users = array ("Bert", " Sharon", "Betty", "Harry" ); $users[] = "sally"; No Associative Arrays Numerically indexed arrays are useful for storing values in the order in which they were added or according to a sort pattern. Sometimes, though, you need to access elements in an array by name. An associative array is indexed with strings between tf or co m er not initialize the intervening elements. This could lead to confusion when attempting cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 111 the square brackets rather than numbers. Imagine an address book. Which would be easier, indexing the "name" field as 4 or as "name"? NEW TERM Arrays indexed by strings are known as associative arrays. You may also see them referred to as hashes. Once again, you can define an associative array using either array() or the array Tip The division between an associative array and a numerically indexed hashes are in Perl. It is a good idea, nevertheless, to treat them manipulation. Defining Associative Arrays with the array() Function array is not absolute in PHP. They are not separate types as arrays and separately. Each demands different strategies for n access To define an associative array with the array() function, you must define both the key and value for each element. The following code creates an associative array called $character with four elements: $character = array ( name=>"bob", age=>30, print $character[age]; The keys in an associative array are strings, but it isn't necessary to surround them with quotation marks unless the key contains more than one word. No Directly Defining or Adding to an Associative Array You can create or add a name/value pair to an associative array simply by assigning a value to a named element. In the following, we re-create our $character array by directly assigning a value to each key: tf or co We can now access any of the fields of $character: m er "special power"=>"x-ray vision" ); cia l, occupation=>"superhero", http://i-tronics.blogspot.com/ us e fo re du ca tio on ly and identifier []. 112 $character[name] = "bob"; $character[occupation] = "superhero"; $character[age] = 30; $character["special power"] = "x-ray vision"; Until now, we've simply said that elements of arrays are values. In our $character array, three of the elements held strings, and one held an integer. The reality is a little more complex, however. In fact, an element of an array could be a value, an Imagine an array that stores an array in each of its elements. To access the third element of the second element, you would have to use two indices: $array[1][2] NEW TERM multidimensional arrays. Arrays that contain arrays as their elements are known as The fact that an array element can itself be an array enables you to create sophisticated data structures relatively easily. 7.1 defines an array that has an Listing 7.1: Defining a Multidimensional Array 1: 2: 4: 5: 6: Listing 7.1 associative array as each of its elements. 7: $characters = array ( or tf No co m er array ( name=>"bob", occupation=>"superhero", age=>30, specialty=>"x-ray vision" ), array ( name=>"sally", occupation=>"superhero", age=>24, specialty=>"superhuman strength" ), array ( name=>"mary", occupation=>"arch villain", age=>63, specialty=>"nanotechnology" ) http://i-tronics.blogspot.com/ cia l, us e fo re du ca tio object, or even another array. A multidimensional array is an array of arrays. n on ly Multidimensional Arrays 113 20: 21: 22: print $characters[0][occupation]; 23: // prints "superhero" 24: ?> 25: 26: ); Notice that we have nested array function calls within an array function call. At the array. top-level array. We can then go ahead and access any of the associative array's fields. $user[2][name] will be "mary", and $user[2][age] will be 63. When this concept is clear, it will be easy to create complex combinations of associative and numerically indexed arrays. So far, you've seen the ways in which you can create and add to arrays. In this section, you will examine some of the tools that PHP4 provides to allow you to acquire information about arrays and access their elements. Getting the Size of an Array print $user[4] Because of the flexibility of arrays, however, you won't always know how many play. count() returns the number of elements in an array. In the following code, we define a numerically indexed array and use count() to access its last element: $users = array ("Bert", "Sharon", "Betty", "Harry" ); No print $users[count($users)− 1]; Notice that we subtract 1 from the value returned by count(). This is because count() returns the number of elements in an array, not the index of the last element. tf elements a particular array contains. That's where the count() function comes into or co You can access an element of an array by using its index: m er cia l, http://i-tronics.blogspot.com/ us e Accessing Arrays fo re du ca Accessing $user[2], therefore, gives us access to the third associative array in the tio n first level, we define an array. For each of its elements, we define an associative on ly 114 Although arrays are indexed from zero by default, it is possible to change this. For the sake of clarity and consistency, however, this is not usually advisable. Looping Through an Array examples, you'll use PHP4's powerful foreach statement. You will examine some other methods inHour 16. Note The foreach statement was introduced with PHP4. In the context of numerically indexed arrays, you would use a foreach statement foreach( $array as $temp ) { //... } In the following code, we define a numerically indexed array and use foreach to access each of its elements in turn: $users = array ("Bert", "Sharon", "Betty", "Harry" ); { } You can see the output from this code fragment in Figure 7.1. No tf or co print "$val
"; m er foreach ( $users as $val ) cia l, http://i-tronics.blogspot.com/ us you will temporarily store each element. e where $array is the array you want to loop through, and $temp is a variable in which fo re du ca like this: tio n on ly There are many ways of looping through each element of an array. For these 115 Figure 7.1: Looping through an array. The value of each element is temporarily placed in the variable $val, which we then print to the browser. If you are moving to PHP4 from Perl, be aware of a significant difference in the behavior of foreach. Changing the value of the temporary variable in a Perl foreach loop changes the corresponding element in the array. Changing the temporary variable in the preceding example would have no effect on the $users array. You will look at a way of using foreach to change the values of a numerically indexed array inHour 16 Looping Through an Associative Array To access both the keys and values of an associative array, you need to alter the use of foreach slightly. In the context of associative arrays, you would use a foreach statement like this: foreach( $array as $key=>$value ) { //... No where $array is the array we are looping through, $key is a variable that temporarily holds each key, and $value is a variable that temporarily holds each value. Listing 7.2 creates an associative array and accesses each key and value in turn. Listing 7.2: Looping Through an Associative Array with foreach 1: 2: tf or } co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 116 3: 4: 5: 6: "bob", occupation=>"superhero", age=>30, "special power"=>"x-ray vision" ); 13: foreach ( $character as $key=>$val ) 14: 15: 16: 17: 18: ?> 19: 20: { print "$key = $val
"; } You can see the output from Listing 7.2 in Figure 7.2. Outputting a Multidimensional Array through each of its elements. No tf created in Listing 7.1. Listing 7.3 defines a similar array and uses foreach to loop or You can now combine these techniques to output the multidimensional array co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 117 Figure 7.2: Looping through an associative array. 1: 2: 3: 4: 5: 6: "superhero", or tf No 17: 18: 19: 20: 21: co m er age=>30, specialty=>"x-ray vision" ), array ( name=>"sally", occupation=>"superhero", age=>24, specialty=>"superhuman strength" ), array ( name=>"mary", occupation=>"arch villain", age=>63, specialty=>"nanotechnology" ) ); cia l, array ( name=>"bob", http://i-tronics.blogspot.com/ us e fo re du ca Listing 7.3: Looping Through a Multidimensional Array tio n on ly 118 22: foreach ( $characters as $val ) 23: 24: 25: 26: 27: 28: 29: 30: ?> 31: 32: { foreach ( $val as $key=>$final_val ) { print "$key: $final_val
"; } print "
"; } You can see the output from Listing 7.3 in Figure 7.3. We create two foreach loops. The outer loop accesses each element in the numerically indexed array $users, placing each one in $val. Because $val itself then contains an associative array, we can loop through this, outputting each of its elements (temporarily stored in $key Figure 7.3: Looping through a multidimensional array. No For this technique to work as expected, we need to make sure in advance that $val will always contain an array. To make this code a little more robust, we could use the function is_array() to test $val. is_array() accepts a variable, returning true if the variable is an array, or false otherwise. Manipulating Arrays http://i-tronics.blogspot.com/ tf or co m er cia l, us and $final_val) to the browser. e fo re du ca tio n on ly 119 You can now populate arrays and access their elements, but PHP4 has functions to help you do much more than that with arrays. If you're used to Perl, you'll find some of these eerily familiar! Joining Two Arrays with array_merge() array_merge() accepts two or more arrays and returns a merged array combining second to the first, and loop through the resultant third array: $first = array("a", "b", "c"); $second = array(1,2,3); $third = array_merge( $first, all their elements. In the following example, we create two arrays, joining the $second ); foreach ( $third as $val ) { print "$val
"; } The $third array contains copies of all the elements of both the $first and $second browser with a
tag between each element. Remember that the arrays passed to array_merge() are not themselves transformed. Note The array_merge() function was introduced with PHP4. Adding Multiple Variables to an Array with array_push() array_push() accepts an array and any number of further parameters, each of array_merge() in that the array passed in as the first argument is transformed. array_push() returns the total number of elements in the array. Let's create an array and add some more values to it: No $first = array("a", "b", "c"); $total = array_push( $first, 1, 2, 3 ); print "There are $total elements in \$first

"; tf which is added to the array. Note that the array_push() function is unlike or co m er cia l, arrays. The foreach statement prints this combined array ( 'a', 'b', 'c', 1, 2, 3 ) to the http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 120 foreach ( $first as $val ) { print "$val
"; } transforms, we are able to store this value (6) in a variable and print it to the browser. The $first array now contains its original elements as well the three browser within the foreach statement. you use a dollar sign followed by numbers and letters within a string, PHP will attempt to insert the value of a variable by that name. In the example above we wished to print the string '$first' rather than the value of the $first variable. To print the special character '$', therefore, we must precede it with a backslash. PHP will now print the character instead of interpreting it. This process is often referred to as "escaping" a character. Caution Perl users beware! If you're used to working with Perl's push(), you array_push() it will be added as a single element, creating a array_merge(). argument. In the following example, we use array_shift() in conjunction with a contains elements: No "; tf or while loop. We test the value returned from count() to check whether the array still co array_shift() removes and returns the first element of an array passed to it as an m er Removing the First Element of an Array with array_shift() cia l, multidimensional array. If you want to combine two arrays, use http://i-tronics.blogspot.com/ us should note that if you pass a second array variable to e fo re du ca Notice that we used a backslash character when we printed the string "\$first". If tio n integers we passed to the array_push() function, all of these are printed to the on ly Because array_push() returns the total number of elements in the array it 121 print "there are ".count($an_array)." elements in \$an_array
"; } ?> You can see the output from this fragment of code in Figure 7.4. Figure 7.4: Using array_shift() to remove and print every element in an array. array_shift() is useful when you need to create a queue and act on it until the queue is empty. of PHP4. Note The array_shift() function was added to the language with the advent Slicing Arrays with array_slice() array_slice() allows you to extract a chunk of an array. It accepts an array as an argument, a starting position (offset), and an (optional) length. If the length is starting position onward returned. array_slice() does not alter the array you pass to omitted, array_slice() generously assumes that you want all elements from the it. It returns a new array containing the elements you have requested. No from it: $first = array("a", "b", "c", "d", "e", "f"); $second = array_slice($first, 2, 3); foreach ( $second as $var ) { print "$var
"; tf In the following example, we create an array and extract a new three-element array or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 122 } This will print the elements 'c', 'd', and 'e', separating each by a
tag. Notice that the offset is inclusive if we think of it as the index number of the first element we are requesting. In other words, the first element of the $second array is equivalent to $first[2]. If we pass array_slice() an offset argument that is less than zero, the returned slice will begin that number of elements from the end of the given array. the end of the given array. Note Once again, array_slice() was added to PHP with PHP4. Sorting Arrays Sorting is perhaps the greatest magic you can perform on an array. Thanks to the functions that PHP4 offers to achieve just this, you can truly bring order from chaos. indexed and associative arrays. This section introduces some functions that allow you to sort both numerically Sorting Numerically Indexed Arrays with sort() strings are present or numerically if all elements are numbers. The function doesn't return any data, transforming the array you pass it. Note that it differs from Perl's sort() function in this respect. The following fragment of code initializes an array of single character strings, sorts it, and outputs the transformed array: $an_array = array("x","a","f","c"); sort( $an_array); No foreach ( $an_array as $var ) { tf Caution Don't pass an associative array to sort(). You will find that the values are sorted as expected but that your keys have been or print "$var
"; } co m er sort() accepts an array as its argument and sorts it either alphabetically if any cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio will contain all elements from the offset position to that number of elements from n If we pass array_slice() a length argument that is less than zero, the returned slice on ly 123 lost— replaced by numerical indices that follow the sort order. You can reverse sort a numerically indexed array by using rsort() in exactly the same way as sort(). Sorting an Associative Array by Value with asort() asort() accepts an associative array and sorts its values just as sort() does. However, it preserves the array's keys: $first = array("first"=>5,"second"=>2,"third"=>1); asort( $first ); foreach ( $first as $key => $val ) { print "$key = $val
"; } You can reverse sort an associative array by value with arsort(). No Sorting an Associative Array by Key with ksort() ksort() accepts an associative array and sorts its keys. Once again, the array you pass it will be transformed and nothing will be returned: $first = array("x"=>5,"a"=>2,"f"=>1); tf or Figure 7.5: Sorting an associative array by its values with asort(). co m er cia l, http://i-tronics.blogspot.com/ us You can see the output from this fragment of code in Figure 7.5. e fo re du ca tio n on ly 124 ksort( $first ); foreach ( $first as $key => $val ) { print "$key = $val
"; } You can see the output from this fragment of code in Figure 7.6. You can reverse sort an associative array by key with krsort(). In this hour, you learned about arrays and some of the many tools that PHP4 indexed and associative arrays, and output data from them using a foreach loop. through the information they contain. You learned how to manipulate arrays by that PHP4 makes available to sort arrays. No Q&A Q If the foreach statement was introduced with PHP4, how did programmers using PHP3 iterate through arrays? A The PHP3 technique for looping through an array involved a function called each(), which was used in conjunction with a while statement. You can read about this technique inHour 16. Q Are there any functions for manipulating arrays that we have not tf or adding or removing multiple elements. Finally, you learned some of the techniques co You should be able to combine arrays to create multidimensional arrays and loop m er provides to work with them. You should now be able to create both numerically cia l, Summary http://i-tronics.blogspot.com/ us e Figure 7.6: Sorting an associative array by its keys with ksort(). fo re du ca tio n on ly 125 covered here? A PHP4 supports many array functions. You can read about some more of these in Hour 16 and find them all in the official PHP manual at http://www.php.net/manual/ref.array.php. Q I can discover the number of elements in an array, so should I use a for statement to loop through an array? A You should be cautious of this technique. You cannot be absolutely sure that the array you are reading is indexed by consecutively numbered keys. The Workshop provides quiz questions to help you solidify your understanding of the material covered. Try to understand the quiz answers before continuing to the next hour's lesson. Quiz answers are provided in Appendix A. Quiz What function can you use to define an array? What is the index number of the last element of the array defined below? $users = array("Harry", "Bob", "Sandy"); "Susan" to the $users array defined previously? Which function could you use to add the string "Susan" to the $users array? In PHP4, what is the simplest way of looping through an array? What function would you use to join two arrays? How would you sort an associative array by its keys? How would you find out the number of elements in an array? No tf Create a multidimensional array of movies organized by genre. This should take the form of an associative array with genres as keys ("SF", "Action", "Romance", and so on). Each of this associative array's elements should be an array containing movie names ("2001", "Alien", "Terminator", and so on). Loop through the array you created in Activity 1, outputting each genre and its associated movies to the browser. or Activities co m er cia l, Without using a function, what would be the easiest way of adding the element http://i-tronics.blogspot.com/ us e fo re du ca tio Workshop n on ly 126 Hour 8: Objects Overview Object-oriented programming is dangerous. It changes the way you think about coding, and once the concepts have a hold on you, they don't let go. PHP, like Perl before it, has progressively incorporated more object-oriented aspects into its object-oriented code at the heart of your projects. syntax and structure. With the advent of PHP4, it becomes possible to use Throughout this hour, you'll take a tour of PHP4's object-oriented features and apply them to some real-world code. In this hour, you will learn What objects and classes are How to create classes and instantiate objects How to create and access properties and methods How to create classes that inherit functionality from others your projects An object is an enclosed bundle of variables and functions forged from a special template called a class. Objects hide a lot of their inner workings away from the them orders and they can return information. These interfaces are special functions called methods. All the methods of an object have access to special variables called properties. By defining a class, you lay down a set of characteristics. By creating objects of that type, you create entities that share these characteristics but might initialize them as would have a color characteristic. All automobile objects would share the characteristic of color, but some would initialize it to "blue," others to "green," and so on. A class is a collection of special functions called methods and special variables called properties. You can declare a class with the class keyword. Classes are the templates from which objects are created. NEW Existing in memory rather than as code, an object is an instance of a different values. You might create an automobile class, for example. This class code that uses them, providing instead easy interfaces through which you can send No tf or co m er cia l, What Is an Object? http://i-tronics.blogspot.com/ us e Some of the reasons why object-oriented programming can help you to organize fo re du ca tio n on ly 127 TERM class. That is, an object is the working embodiment of the functionality laid down in a class. An object is instantiated with the new statement in conjunction with the name of the class of which it is to be a member. When an object is instantiated, you can access all its properties and all its methods. Perhaps the greatest benefit of object-oriented code is its reusability. Because the classes used to create objects are self-enclosed, they can be easily pulled from one project and used in another. Additionally, it is possible to create child classes that inherit and override the characteristics of their parents. This technique can allow base functionality while adding more of their own. Creating an Object To create an object, you must first design the template from which it can be instantiated. This template is known as a class, and in PHP4 it must be dec lared with the class keyword: class first_class { // a very minimal class } The first_class class is the basis from which you can instantiate any number of statement: No print "\$obj1 is a ".gettype($obj1)."
"; print "\$obj2 is a ".gettype($obj2)."
"; You can test that $obj1 and $obj2 contain objects with PHP's gettype() function. gettype() accepts any variable and returns a string that should tell you what you are dealing with. In a loosely typed language like PHP, gettype() is useful when tf $obj2 = new first_class(); or $obj1 = new first_class(); co first_class objects. To create an instance of an object, you must use the new m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca Perhaps the best way to explain object-oriented programming is to do it. tio n you to create progressively more complex and specialized objects that can draw on on ly 128 checking arguments sent to functions. In the previous code fragment, gettype() returns the string "object", which is then written to the browser. So, you have confirmed that you have created two objects. Of course they're not very useful yet, but they help to make an important point. You can think of a class as a mold with which you can press as many objects as you want. Let's add some more features to the class to make your objects a little more interesting. Object Properties at the top. A property can be a value, an array, or even another object: class first_class { var $name = "harry"; } Notice that we declared our variable with the var keyword. This is essential in the context of a class, and you will be rewarded with a parse error if you forget it. Now any first_class object that is created will contain a property called name with the value of "harry". You can access this property from outside the object and even change it: class first_class { } var $name = "harry"; $obj1 = new first_class(); $obj2 = new first_class(); $obj1->name = "bob"; print "$obj2->name
"; The -> operator allows you to access or change the properties of an object. No Although $obj1 and $obj2 were born with the name of "harry", we have helped $obj2 to change its mind by assigning the string "bob" to its name property, before using the -> operator once again to print each object's name property to the screen. Caution Object-oriented languages, such as Java, demand that the programmer set a level of privacy for all properties and methods. This means that access can be limited to only those features needed to use the object effectively, and properties meant only for internal use can tf or print "$obj1->name
"; co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio anywhere within the body of your class, but for the sake of clarity should be defined n Objects have access to special variables called properties. These can be declared on ly 129 be safely tucked away. PHP has no such protection. You can access all the fields of an object, which can cause problems if a property isn't meant to be changed. You can use objects to store information, but that makes them little more interesting than associative arrays. In the next section, you will look at object methods, and your objects can get a little more active. Object Methods A method is a function defined within a class. Every object instantiated from the first_class class. Listing 8.1: A Class with a Method 1: 2: 3: 4: 5: sayHello(); 17: // outputs "hello" 18: ?> 19: No 20: As you can see, a method looks and behaves much like a normal function. A method is always defined within a class, however. You can call an object method using the -> operator. Importantly, methods have access to the class's member variables. You've already seen how to access a property from outside an object, but how does an object refer to itself? Find out in Listing 8.2. tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n class will have the method's functionality. Listing 8.1 adds a method to the on ly 130 Listing 8.2: Accessing a Property from Within a Method 1: 2: 3: 4: 5: sayHello(); 17: // outputs "hello my name is harry" 18: ?> 19: 20: } { var $name="harry"; function sayHello() { print "hello my name is $this->name
"; } A class uses the special variable $this to refer to the currently instantiated object. You can think of it as a personal pronoun. Although you refer to an object by the means of the $this variable. Combining the $this variable and the -> operator, you can access any property or method in a class from within the class itself. Imagine that you want to assign a different value to the name property to every object of type first_class you create. You could do this by manually resetting the name property as you did earlier, or you could create a method to do it for you, as Listing 8.3: Changing the Value of a Property from Within a Method 1: 2: shown in Listing 8.3. handle you have assigned it to ($obj1, for example), an object must refer to itself by No tf 3: 4: 5: 6: setName("william"); 23: $obj1->sayHello(); 25: ?> 26: 27: } { var $name="harry"; function setName( $n ) { $this->name = $n; } function sayHello() { print "hello my name is $this->name
"; } 24: // outputs "hello my name is william" The name property of the object begins as "harry", but after the object's setName() method is called, it is changed to "william". Notice how the object is capable of in exactly the same way as you would to a function. We're still missing a trick here, however. If you create a method with exactly the same name as the first_class class, it will automatically be called when a new object is instantiated. In this way, you can give your objects arguments to process at the moment you instantiate them. Objects can run code to initialize themselves based Listing 8.4 adds a constructor to the first_class class. 1: 2: 3: 4: 5: on these arguments or other factors. These special methods are called constructors. adjusting its own property. Notice also that you can pass arguments to the method No Listing 8.4: A Class with a Constructor tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 132 6: name = $n; } function sayHello() { print "hello my name is $this->name
"; } 19: $obj1 = new first_class("bob"); 20: $obj2 = new first_class("harry"); 21: $obj1->sayHello(); 22: // outputs "hello my name is bob" 23: $obj2->sayHello(); 24: // outputs "hello my name is harry" 25: ?> 26: 27: The first_class() constructor method is automatically called when we instantiate a parameter if we don't include an argument when we create our object. An Example more useful. We will create a class that can maintain a table of fields, organized in No named columns. This data should be built up on a row-by-row basis, and crude a method should be included so that the data can be written to the browser. Neatly formatting the data is not necessary at this stage. tf Let's bring these techniques together to create an example that might be a little or co m er first_class object. We set up a default so that the string "anon" is assigned to the cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 133 Defining the Class's Properties First, we must decide what properties we need to store the data in. We will keep the column names in an array and the rows in a multidimensional array. We'll also store with: class Table { var $table_array = array(); var $headers = array(); var $cols; } Creating a Constructor an integer so that we can easily keep track of the number of columns we're dealing We can do this in the constructor by asking for an array of strin gs as a parameter. result to the cols property: function Table( $headers ) { $this->headers = $headers; $this->cols = count ( $headers ); } created, we will know right away the number of columns we'll be storing and the No name of each column. Because this information has been stored in properties, it will be available to all the object's methods. tf Assuming that the correct information is provided when the new Table object is or co m er cia l, Armed with this information, we can calculate the number of columns and assign the http://i-tronics.blogspot.com/ us We need to get the names of the columns that we'll be working with straight away. e fo re du ca tio n on ly 134 The addRow() Method The Table object accepts each row of data in the form of an array, assuming, of course, that this information is provided in the same order as that of the column names: function addRow( $row ) { if ( count ($row) != $this->cols ) return false; array_push($this->table_array, $row); return true; } The addRow() method expects an array, which is stored in a parameter variable called $row. We have stored the number of columns that the object expects to the right number of elements using the count() function. If it doesn't, a boolean bfalse is returned. handle in the $cols property. We can check that the $row array parameter contains We then use PHP4's array_push() function to add the row array to the table_array property. array_push() accepts two arguments— an array to add to and the value to element of the first array, creating a multidimensional array. In this way, we can build up an array of arrays. push onto it. If the second argument is itself an array, it will be added as a single The addRowAssocArray() Method The addRow() method is fine as long as the elements of the array passed to it are No ordered correctly. The addRowAssocArray() method allows for a little more flexibility. It expects an associative array. The keys for each value should match one of the header names we are storing in our headers property, or they'll be ignored: function addRowAssocArray( $row_assoc ) { $row = array(); tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 135 foreach ( $this->headers as $header ) { if ( ! isset( $row_assoc[$header] )) $row_assoc[$header] = ""; $row[] = $row_assoc[$header]; } array_push($this->table_array, $row); return true; } The associative array passed to addRowAssocArray() is stored in the parameter variable $row_assoc. We create an empty array called $row to store the values that we will eventually add to the table_array property. We loop through the headers array to check that a value corresponding to each string exists in the $row_assoc array. To do this, we use the PHP4 function isset(), which expects any variable as its argument. It returns true if the variable passed to it has been set and false otherwise. We pass isset() the element in the $row_assoc array whose key is the by that string exists in $row_assoc, we go ahead and create one with the value of an element in $row_assoc indexed by the current string in the headers array. By the time we have finished looping through the headers array property, $row contains an of any omissions. ordered copy of the values passed to us in $row_assoc, with empty strings in place current value in the headers property we are looping through. If no element indexed empty string. We can then continue to build up our $row array, adding to it the object's table_array property. All we need now is a way of outputting the data. The output() Method No The output() method writes both the headers and the table_array array properties to the browser. This method is provided mainly for the purpose of debugging. You'll see a more satisfactory solution later in the hour. function output() { print "

"; tf or co We now have two simple methods to allow the addition of rows of data to a Table m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 136 foreach ( $this->headers as $header ) print "$header print "\n"; foreach ( $this->table_array as $y ) { foreach ( $y as $xcell ) print "$xcell print "\n"; } print "

"; } "; "; This code fragment should be fairly self-explanatory. We loop first through the headers array property, writing each element to the screen. We then do the same for the table_array property. Because the table_array property is a two-dimensional array, each of its elements is itself an array that must be looped through within the main loop. Bringing It All Together Listing 8.5 includes the entire Table class, as well the code that instantiates a Table Listing 8.5: The Table Class 2: No 10: tf 4: 5: 6: Listing 8.5 co 1: m er object and calls each of its methods. cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 137 11: 12: 13: 14: 15: 16: 17: 18: 19: 20: 21: 22: 23: 24: 25: function addRow( $row ) { if ( count ($row) != $this->cols ) return false; var $cols; function Table( $headers ) { $this->headers = $headers; $this->cols = count ( $headers ); } array_push($this->table_array, $row); return true; } 27: 28: 29: 30: 31: 32: 33: 34: 35: 36: 37: { $row = array(); foreach ( $this->headers as $header ) or tf No 38: 39: 40: function output() { co array_push($this->table_array, $row); return true; } m er { if ( ! isset( $row_assoc[$header] )) $row_assoc[$header] = ""; $row[] = $row_assoc[$header]; } cia l, http://i-tronics.blogspot.com/ us 26: function addRowAssocArray( $row_assoc ) e fo re du ca tio n on ly 138 41: 42: 43: 44: 45: 46: 47: 48: 49: 50: 51: 52: 53: 54: } print "

"; foreach ( $this->headers as $header ) print "$header "; print "\n"; foreach ( $this->table_array as $y ) { foreach ( $y as $xcell ) print "$xcell "; print "\n"; } print "

"; } 55: $test = new table( array("a","b","c") ); 56: $test->addRow( array(1,2,3) ); 57: $test->addRow( array(4,5,6) ); 58: $test->addRowAssocArray( array ( b=>0, a=>6, c=>3 ) ); 59: $test->output(); 60: ?> 61: 62: You can see the output of Listing 8.5 in Figure 8.1. No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 139 Figure 8.1: The Table object in action. The output looks neat as long as the individual strings are the same length. This will change if we vary the length of any of the elements. What's Missing? Although this class will do a job effectively for us, with more time and space, we Because PHP is loosely typed, it is our responsibility to make sure that parameters the data functions covered in Hour 16, "Working with Data." We might also want to make the Table object a little more flexible, adding methods to sort the rows according to the values in any column before we output, for example. Why a Class? manipulating arrays ourselves as and when we need to? It certainly isn't efficiency. We've added overheads to the process of storing and retrieving information. No First, this code is reusable. It has a clear purpose— to represent data in a certain way, and we can now slot it into any project that needs data stored and output in this way. Second, a Table object is active. We can ask it to output its data without bothering to write code to loop through its table_array property. tf or So, what's better about using an object to achieve this task than simply co m er cia l, passed to our methods are the type we are expecting. For this purpose, we can use http://i-tronics.blogspot.com/ us e might have added some features and safeguards. fo re du ca tio n on ly 140 Third, we've built an interface to the object's functionality. If we decide later to optimize the code in the class, we can do so without disturbing the rest of the project, as long as the same methods remain, expecting the same arguments and returning the same data types. Finally, we can build classes that inherit, extend, and override its functionality. This To create a class that inherits functionality from a parent class, we need to alter our Listing 8.6: Creating a Class That Inherits from Another 1: 2: 3: 4: 5: 6: name
"; } co $this->name = $n; } m er var $name = "harry"; cia l, http://i-tronics.blogspot.com/ us e fo re du ca class declaration slightly. Listing 8.6 returns to our simple example. tio n Inheritance on ly makes object-oriented code truly cool. 141 21: 22: 23: 24: 25: $test = new second_class("son of harry"); 26: $test->sayHello(); 27: // outputs "Hello my name is son of harry" 28: ?> 29: 30: } { In addition to the simple first_class class, we have created an even more basic second_class class. Notice the extends clause in the class declaration. This means that a second_class object inherits all the functionality laid down in the first_class class. Any second_class object will have a sayHello() method and a name property just as any first_class object would. If that's not enough, there's even more magic to be found in Listing 8.6. Notice that we didn't define a constructor method for the second_class class. So, how was the name property changed from the default, "harry" to the value passed to the second_class class, "son of harry"? Because we didn't provide a constructor, the Note If a class extending another doesn't contain a constructor method, the parent class's constructor method will be called automatically when a child object is created. This feature is new in PHP4. first_class class's constructor was automatically called. No The second_class class currently creates objects that behave in exactly the same methods of their parents, allowing objects instantiated from them to behave differently, while otherwise retaining much of the same functionality. Listing 8.7 gives the second_class class its own sayHello() method. Listing 8.7: The Method of a Child Class Overriding That of Its Parent 1: way as first_class objects. In object-oriented code, child classes can override the tf or Overriding the Method of a Parent Class co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 142 2: 3: 4: 5: 6: name = $n; } function sayHello() { print "Hello my name is $this->name
"; 20: class second_class extends first_class 22: 23: 24: 25: 26: function sayHello() No 27: 28: $test = new second_class("son of harry"); 29: $test->sayHello(); 30: // outputs "I'm not going to tell you my name" 31: ?> tf or } co { print "I'm not going to tell you my name
"; } m er 21: { cia l, http://i-tronics.blogspot.com/ us } e fo re du ca tio n on ly 143 32: 33: The sayHello() method in the second_class class is called in preference to that in the parent class. Calling an Overridden Method the benefit of your own additions. Object-oriented programming allows you to have the method in the first_class class that it has overridden. Listing 8.8: Calling an Overridden Method 1: 2: 3: 4: 5: 6: name
"; } co function first_class( $n ) { $this->name = $n; } m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca your cake and eat it too. In Listing 8.8, the second_class's sayHello() method calls tio Occasionally, you will want the functionality of a parent class's method, as well as n on ly 144 20: class second_class extends first_class 21: 22: 23: 24: 25: 26: 27: 28: 29: $test = new second_class("son of harry"); 30: $test->sayHello(); } { function sayHello() { print "I'm not going to tell you my name -- "; first_class::sayHello(); } 31: // outputs "I'm not going to tell you my name -- Hello my name is son of harry" 32: ?> 33: 34: By using the syntax parentclassname::methodname() we can call any method that we have overridden. This syntax is new to PHP4— the same code will result in a parse error with PHP3. Inheritance: An Example from the Table class created in Listing 8.5. The new class will be called HTMLTable No and will be designed to overcome the deficiencies of Table's output() method. Defining HTMLTable's Properties HTMLTable will format the data that it stores courtesy of Table's functionality using a standard HTML table. For this example, we will allow an HTMLTable's user to tf another. Now we can use some of these techniques to create a class that inherits or You've seen how one class can inherit, override, and extend the functionality of co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 145 change the CELLPADDING argument of the TABLE element and the BGCOLOR argument of the TD element. A real-world example should allow for many more changes than this. class HTMLTable extends Table { var $bgcolor; var $cellpadding = "2"; } We have defined a new class and established that it will inherit from Table by using cellpadding a default value of 2. Creating the Constructor You have already seen that a parent class's constructor is called automatically if you don't define a constructor for a child class. In this case, however, we want to do more work with our constructor than has already been written for the Table class: function HTMLTable( $headers, $bg="#ffffff" ) Table::Table($headers); $this->bgcolor=$bg; } string becomes our bgcolor property, and we give it a default value, making it an to it. Laziness is a virtue in programming, so we let the Table class's constructor do its thing and worry no more about it. We initialize the HTMLObject's bgcolor No property. tf Note If a child class is given a constructor method, the parent's constructor is no longer called implicitly. The child class's constructor must explicitly call that of its parent. or optional argument. We call the Table class's constructor, passing the $header array co The HTMLTable constructor accepts an array of column names and a string. The m er cia l, { http://i-tronics.blogspot.com/ us e fo re du ca the extends clause. We create two properties, bgcolor and cellpadding, giving tio n on ly 146 The setCellpadding() Method A child class can of course create its own entirely new methods. setCellpadding() allows a user to change the cellpadding property from the default. Of course, it object, but this is not good practice on the whole. As a rule of thumb, it is best to complex version of this class, the setCellpadding() method might need to change Unfortunately, there is no neat way of enforcing privacy in PHP4. function setCellpadding( $padding ) { $this->cellpadding = $padding; } The Output() Method would be perfectly possible to set the cellpadding property directly from outside the create methods that will change properties on behalf of an object's user. In a more other properties to reflect the change made to the cellpadding property. The Output() method completely overrides the equivalent method in the Table class. formatting: function output() { print "cellpadding\" border=1>"; foreach ( $this->headers as $header ) No tf or print ""; foreach ( $this->table_array as $row=>$cells ) { print ""; foreach ( $cells as $cell ) print ""; print ""; } co m er cia l, It outputs data according to exactly the same logic as its parent, adding HTML table http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 147 print "

bgcolor\">$header

bgcolor\">$cell

"; } The output() method should be fairly clear if you understood the Table class's version. We loop through both the header and table_array arrays, outputting each to the browser. Crucially, though, we format the data into a table, using the cellpadding and bgcolor properties to change the spacing and color of the table that the end user sees. The Table and HTMLTable Classes in Their Entirety instantiate an HTMLTable object, change its cellpadding property, add some data, and call its ouptut() method. In a real-world example, we would probably get our row data directly from a database. Listing 8.9: The Table and HTMLTable Classes 1: 2: 3: 4: 5: 6: 7: class Table 8: 9: 10: 11: 12: { var $table_array = array(); var $headers = array(); No 13: tf 14: 15: 16: 17: or var $cols; function Table( $headers ) { $this->headers = $headers; $this->cols = count ( $headers ); } co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca Listing 8.9 brings the entire Table and HTMLTable examples together. We also tio n on ly 148 18: 19: 20: 21: 22: 23: 24: 25: 26: 27: 28: 29: 30: 31: 32: 33: 34: 35: 36: 37: 38: 39: 40: 41: 42: 43: function addRowAssocArray( $row_assoc ) { function addRow( $row ) { if ( count ($row) != $this->cols ) return false; array_push($this->table_array, $row); return true; } if ( count ($row_assoc) != $this->cols ) return false; $row = array(); foreach ( $this->headers as $header ) { $row_assoc[$header] = " "; $row[] = $row_assoc[$header]; } } function output() tf No 44: 45: or co { print "

"; foreach ( $this->headers as $header ) print "$header print "\n"; foreach ( $this->table_array as $y ) { "; 46: 47: m er array_push($this->table_array, $row) ; cia l, http://i-tronics.blogspot.com/ us if ( ! isset( $row_assoc[$header] )) e fo re du ca tio n on ly 149 48: 49: 50: 51: 52: 53: 54: 55: 56: class HTMLTable extends Table 57: 58: 59: 60: 61: 62: 63: 64: 65: 66: 67: 68: 69: 70: 71: 72: 73: { var $bgcolor; var $cellpadding = "2"; } foreach ( $y as $xcell ) print "$xcell "; print "\n"; } print "

"; } function HTMLTable( $headers, $bg="#ffffff" ) { Table::Table($headers); $this->bgcolor=$bg; } function setCellpadding( $padding ) { } tf No or 74: 75: 76: 77: co function output() { print "cellpadding\" border=1>"; foreach ( $this->headers as $header ) print ""; foreach ( $this->table_array as $row=>$cells ) { print ""; foreach ( $cells as $cell ) m er $this->cellpadding = $padding; cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 150 78: 79: 80: 81: 82: 83: } print ""; print ""; } print "

bgcolor\">$header

bgcolor\">$cell

"; } 84: $test = new HTMLTable( array("a","b","c"), "#00FF00"); 85: $test->setCellpadding( 7 ); 86: $test->addRow( array(1,2,3)); 87: $test->addRow( array(4,5,6)); 88: $test->addRowAssocArray( array ( b=>0, a=>6, c=>3 )); 89: $test->output(); 90: ?> 91: 92: You can see the output from Listing 8.9 in Figure 8.2. No Figure 8.2: The HTMLTable object in action. Why Use Inheritance? So, why did we split Table from HTMLTable? Surely we could have saved ourselves time and space by building HTML table capabilities into the Table class? The answer lies in flexibility. http://i-tronics.blogspot.com/ tf or co m er cia l, us e fo re du ca tio n on ly 151 Imagine that a client gave you the brief to create a class that can maintain a table of fields, organized in named columns. If you had built a monolithic class that collected and stored the data, customized HTML, and output the result to the browser, all would seem to be well. If the same client came back to you and asked whether the code could be adapted some more methods and properties to make it do this too. A week or so later, the client realizes that she would like the code to be able to send data out as an email, and while you're at it, the company intranet uses a subset of XML; could this be accommodated too? At this stage, including all the functionality considering a complete rewrite of the code. in a single class is beginning to look a little unwieldy, and you would already be Let's try this scenario out with our Table and HTMLTable examples. We have already substantially separated formatting the data from acquiring and preparing it. When our client asks that the code should be capable of outputting to a file, we only need to create a new class that inherits from Table. Let's call it FileTable. We need make XMLTable. Figure 8.3 illustrates the relationship between these classes. no changes at all to our existing code. The same would be true for MailTable and What's more, we know that any object that inherits from Table will have an output() loop through the lot, calling output() without worrying about the mechanics. From a simply by repeatedly calling output()! No Summary It is not possible to introduce you to all the aspects of object-oriented programming in one short hour, but I hope I have introduced you to some of the possibilities. The extent to which you use objects and classes in your projects is a matter of choice. It is likely that heavily object-oriented projects will be somewhat more tf or single array of Table-derived objects, we can write emails, HTML, XML, or plain text, co method, so we can group a bunch of them into an array. When we're ready, we can m er Figure 8.3: The relationship between the Table class and multiple child classes. cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly additionally to write neatly formatted data to a text file, you could probably add 152 resource-intensive at runtime than more traditional code. However, effective deployment of object-oriented techniques can significantly improve the flexibility and organization of your code. Throughout this hour, you learned how to create classes and instantiate objects from them. You learned how to create and access properties and methods. Finally, classes. you learned how to build new classes that inherit and override the features of other understand object-oriented programming to become tio a Q This hour introduced some unfamiliar concepts. Do I really need to good PHP programmer? A The short answer is no. Most PHP scripts use little or no object-oriented code at all. The object-oriented approach won't help you do things that you couldn't otherwise achieve. The benefits of object-oriented programming lie in the organization of your scripts, their reusability, and their extensibility. Even if you decide not to produce object-oriented code, however, you may need to decipher third-party programs that contain classes. This hour should help you understand such code. Q I'm confused by the special variable $this. A Within a class, you sometimes need to call the class's methods or access its properties. By combining the $this variable and the -> operator, you can do both. The $this variable is the handle a class is automatically given to refer to itself and to its components. The Workshop provides quiz questions to help you solidify your understanding of the material covered. Try to understand the quiz answers before continuing to the next No Quiz tf hour's lesson. Quiz answers are provided in Appendix A. How would you declare a class called emptyClass() that has no methods or properties? Given a class called emptyClass(), how would you create an object that is an instance of it? or co Workshop m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca n Q&A on ly 153 How can you declare a property within a class? How would you choose a name for a constructor method? How would you create a constructor method in a class? How would you create a regular method within a class? How can you access and set properties or methods from within a class? How would you access an object's properties and methods from outside the object's class? functionality from another class? Activities What should you add to a class definition if you want to make it inherit Create a class called baseCalc() that stores two numbers as properties. Give it a calculate() method that prints the numbers to the browser. Create a class called addCalc() that inherits its functionality from baseCalc(). Override the calculate() method so that the sum of the properties is printed to the browser. Repeat activity 2, for a class called minusCalc(). Give minusCalc() a calculate to the browser. No tf or co m er cia l, http://i-tronics.blogspot.com/ us e method that subtracts the first property from the second, outputting the result fo re du ca tio n on ly 154 Hour 9: Working with Forms Overview Until now, all examples in this book have been missing a crucial dimension. You can set variables and arrays, create and call functions, and work with objects. All this is meaningless if users can't reach into a language's environment to offer it user input. On the World Wide Web, HTML forms are the principal means by which substantial amounts of information can pass from the user to the server. PHP is designed to acquire and work with information submitted via HTML forms. In this hour, you will learn How to get and use environment variables How to access information from form fields How to work with form elements that allow multiple selections How to create a single document that contains both an HTML form and the PHP code that handles its submission How to save state with hidden fields How to redirect the user to a new page handle them Before you actually build a form and use it to acquire data, you need to make a small A global variable is any variable declared at the "top level" of a script — that is, declared outside a function. All functions are made available in a built-in associative No array called $GLOBALS. This is useful in Listing 9.1 because we can take a peek at all our script's global variables with a single loop. Listing 9.1: Looping Through the $GLOBALS Array 1: 2: 3: 4: tf or detour and look again at global variables. You first met these in Hour 6, "Functions." co Global and Environment Variables m er How to build HTML forms that upload files and how to write the PHP code to cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio information. In this hour, you will look at strategies for acquiring and working with n on ly 155 5: 6: $value ) 11: 12: 13: 14: ?> 15: 16: { print "\$GLOBALS[\"$key\"] == $value
"; } We declare three variables and then loop through the built-in $GLOBALS associative array, writing both array keys and values to the browser. In the output, we were able to locate the variables we defined, but we saw an awful lot more besides these. PHP automatically defines global variables that describe both the server and client environments. These are known, therefore, as environment variables. According to but they can be immensely useful. Table 9.1 lays out some common environment variables. These can be accessed as part of the $GLOBALS array, or directly. Table 9.1: Environment Variables Variable $HTTP_USER_AGENT Contains your system, server, and configuration, the availability of these variables will vary, cia l, The name and Mozilla/4.6 version of the (X11;I;Linux2.2.6-15apmac ppc) client The IP address 158.152.55.35 of the client Whether request GET or POST For requests, encoded to the URL GET name=matt&address=unknown the data the POST was No $QUERY_STRING tf or $REQUEST_METHOD co $REMOTE_ADDR $REQUEST_URI m er send appended The full address /matt/php- http://i-tronics.blogspot.com/ us e fo re du ca Example tio n on ly 156 of the request book/forms/eg9.14.html? including query name=matt string $HTTP_REFERER The address of http://www.test.com/a_page.html the page from request made was which the path to the script currently running. On my system this was as follows: This variable can also be directly accessed as the global variable $PHP_SELF. This will be useful in many of the examples in this hour. We will often include the HTML forms we use in the same page as the PHP code that analyzes the content they submit. We can use $PHP_SELF as the string assigned to the HTML FORM element's ACTION argument, saving us the trouble of hard-coding the name of the page. PHP's $GLOBALS array will become useful in other ways as well. A Script to Acquire User Input For now, we'll keep our HTML separate from our PHP code. Listing 9.2 builds a simple HTML form. 1: 2: 4: 5: Listing 9.2: A Simple HTML Form 3: 7: No 10: 11:
12: 13: 14: 15: tf 8:
9: or 6: <form action="eg9.3.php" method="GET"> co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca /matt/php-book/forms/eg9.1.php tio available to you. The variable $GLOBALS["PHP_SELF"], for example, gives you the n In addition to environment variables, PHP makes some other global variables on ly 157 We define a form that contains a text field with the name "user", a text area with the name "address", and a submit button. It is beyond the remit of this book to cover HTML in detail. If you find the HTML in these examples hard going, take a look at Sams Teach Yourself HTML in 24 Hours or one of the numerous online HTML tutorials. The FORM element's ACTION argument points to a file called eg9.3.php, which processes the form information. Because we haven't added anything more directory on the server as the document that contains our HTML. Listing 9.3 creates the code that receives our users' input. Listing 9.3: Reading Input from the Form in Listing 9.2 1: <html> 2: <head> 4: </head> 5: <body> 6: <?php than a filename to the ACTION argument, the file eg9.3.php should be in the same 3: <title>Listing 9.3 Reading input from the form in Listing 9.2</title> 7: print "Welcome <b>$user</b><P>\n\n"; 9: ?> 10: </body> 11: </html> This is the first script in this book that is not designed to be called by hitting a link 9.3 in a file called eg9.3.php. This file is called when a user submits the form defined in Listing 9.2. In the code, we have accessed two variables, $user and $address. It should come as no surprise that these variables contain the values that the user added to the text field named "user" and the text area named "address". Forms in PHP4 really are as variables that will have the same names as those of the form elements on an HTML page. simple as that. Any information submitted by a user will be available to you in global No Accessing Input from Multiple SELECT Elements The examples so far enable us to gather information from HTML elements that submit a single value per element name. This leaves us with a problem when working with tf or co SELECT elements. These elements make it possible for the user to m er or typing directly into the browser's location field. We include the code from Listing cia l, http://i-tronics.blogspot.com/ us e 8: print "Your address is:<P>\n\n<b>$address</b>"; fo re du ca tio n on ly 158 choose multiple items. If we name the <select name="products" multiple> the script that receives this data will only have access to a single value corresponding to this name. We can change this behavior by renaming any elements of this kind so that its name ends with an empty set of square brackets. We do this in Listing 9.4. Listing 9.4: An HTML Form Including a SELECT Element 1: <html> 2: <head> 4: </head> 5: <body> 7: <input type="text" name="user"> 8: <br> 10: 11:
13: Sonic Screwdriver 14: Tricorder 15: ORAC AI 17: 18:
20: 21: 22: 16: HAL 2000 6:

SELECT element with plain name 9: 19: <input type="submit" value="hit it!"> No "products[]" tf In the script that processes the form input, we now find that input from the element will be available in an array called or co m er cia l, us e 12: <select name="products[]" multiple> fo re du ca $products. We demonstrate this in Listing 9.5. Listing 9.5: Reading Input from the Form in Listing 9.4 1: <html> 2: <head> 3: <title>Listing 9.5 Reading input from the form in Listing 9.4</title> 4: </head> http://i-tronics.blogspot.com/ tio n 3: <title>Listing 9.4 An HTML form including a SELECT element</title> on ly 159 5: <body> 6: <?php 7: print "Welcome <b>$user</b><p>\n\n"; 8: print "Your address is:<p>\n\n<b>$address</b><p>\n\n"; 9: print "Your product choices are:<p>\n\n"; 10: print "<ul>\n\n"; 11: foreach ( $products as $value ) 12: 13: 14: 16: ?> 17: </body> 18: </html> { print "<li>$value<br>\n"; } 15: print "</ul>"; The SELECT element is not the only one that allows for multiple values. By giving a number of check boxes the same name, you can allow a user to choose many values within a single field name. As long as the name you choose ends with empty replace the SELECT element in Listing 9.4 with a series of check boxes to achieve exactly the same effect: <input type="checkbox" name="products[]" value="Sonic Screwdriver"> Sonic Screwdriver<br> <input type="checkbox" name="products[]" value="Tricorder">Tricorder<br> <input type="checkbox" name="products[]" value="HAL 2000">HAL 2000<br> square brackets, PHP compiles the user input for this field into an array. We can Accessing All the Fields from a Form in an Associative Array The techniques you have looked at so far work well, as long as your script knows in changes in a form or even service more than one form, without worrying itself about No the names of specific form fields. The global variables that PHP4 makes available provide the solution to this problem. According to whether or not a submitting form used the GET or POST method, you will have access to one or both of $HTTP_GET_VARS or $HTTP_POST_VARS. These are associative arrays that contain the name/value pairs submitted. Listing 9.6 takes advantage of this to list all the fields submitted from a form via a GET request. tf advance what fields to expect. You may often want to write code that can adapt to or co m er <input type="checkbox" name="products[]" value="ORAC AI">ORAC AI<br> cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 160 Listing 9.6: Reading Input from Any Form Using the $HTTP_GET_VARS Array 1: <html> 2: <head> 3: <title>Listing 9.6 Reading input from any form using the $HTTP_GET_VARS 4: </head> 5: <body> 6: <?php 7: foreach ( $HTTP_GET_VARS as $key=>$value ) 8: 9: 10: 11: ?> 12: </body> 13: </html> { print "$key == $value<BR>\n"; } This code lists the names and values of all parameters passed to it via a GET been set up to resolve to arrays. If we were to amend the HTML form in Listing 9.4 that includes a multiple SELECT element to point to the script in Listing 9.6, we user == Matt Zandstra products == Array would typically get the following output when the form was submitted: address == London, England The products array exists in the $HTTP_GET_VARS[products] array item, but we haven't yet written code to take account of this eventuality. Listing 9.7 tests the data type of each of the elements in $HTTP_GET_VARS and amends the output accordingly. array Listing 9.7: Reading Input from Any Form Using the $HTTP _GET_VARS No tf 1: <html> 2: <head> 3: <title>Listing 9.7 Reading input from any form using the $HTTP_GET_VARS array</title> 4: </head> 5: <body> 6: <?php or co m er cia l, http://i-tronics.blogspot.com/ us e transaction. Of course, it's not yet smart enough to deal with parameters that have fo re du ca tio n on ly array</title> 161 7: foreach ( $HTTP_GET_VARS as $key=>$value ) 8: 9: 10: 11: 12: 13: 14: 15: 16: 17: 18: 19: 20: ?> 21: </body> 22: </html> } } else { print "$key == $value<br>\n"; } { if ( gettype( $value ) == "array" ) { print "$key == <br>\n"; foreach ( $value as $two_dim_value ) print ".........$two_dim_value<br>"; As before, we use foreach to loop through the $HTTP_GET_VARS array. We use the itself an array, we create a second foreach statement to loop through it, outputting each value to the browser. Distinguishing Between GET and POST Transactions To work flexibly, a script that can accept data from any source must be able to are entirely portable, however, you can take advantage of the fact that the $HTTP_POST_VARS array will only be present if a POST request has been No Listing 9.8 amends our form parser script to work with the correct array every time. Listing 9.8: Extracting Parameters from Either a GET or POST Request 1: <html> 2: <head> 3: <title>Listing 9.8 Extracting parameters from 4: either a GET or POST request</title> 5: </head> tf made. or co $HTTP_GET_VARS or $HTTP_POST_VARS arrays. On most systems, you can discover whether you are dealing with a GET or POST transaction in the environment variable $REQUEST_METHOD, which should contain the string "post" or "get". To be absolutely sure that your scripts m er decide whether to read the cia l, http://i-tronics.blogspot.com/ us e gettype() function to ascertain whether each of its values is an array. If the value is fo re du ca tio n on ly 162 6: <body> 7: <?php 8: $PARAMS = ( isset( $HTTP_POST_VARS ) ) 9: 11: 12: 13: 14: 15: 16: 17: 18: 19: 20: 21: 22: 23: ?> 24: </body> 25: </html> } } else { } ? $HTTP_POST_VARS : $HTTP_GET_VARS; { if ( gettype( $value ) == "array" ) { print "$key == <br>\n"; foreach ( $value as $two_dim_value ) print ".........$two_dim_value<br>" 10: foreach ( $PARAMS as $key=>$value ) print "$key == $value<br>\n"; Combining HTML and PHP Code on a Single Page No page as a hard-coded HTML form. Such a combination can be useful if you need to present the same form to the user more than once. You would have more flexibility if you were to write the entire page dynamically, of course, but you would miss out on one of the great strengths of PHP. The more standard HTML you can leave in your pages, the easier they will be for designers and page builders to amend without reference to you. You should avoid scattering substantial chunks of PHP code throughout your documents, however. This will make them hard to read and tf In some circumstances, you may want to include form-parsing code on the same or co $PARAMS. Using the built-in isset() function, we first check whether the $HTTP_POST_VARS array has been set. isset() returns true if the variable it is passed has been defined. If the $HTTP_POST_VARS array has been defined, the ternary expression resolves to this; otherwise, it resolves to $HTTP_GET_VARS. We can now use the $PARAMS array throughout the rest of the script without worrying about whether it has been populated as the result of a GET or a POST request. m er cia l, We use the ternary operator to set a variable called http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 163 maintain. Where possible you should create functions that can be called from within your HTML code, and can be reused in other projects. For the following examples, imagine that we are creating a site that teaches basic math to preschool children and have been asked to create a script that takes a number from form input and tells the user whether it is larger or smaller than a predefined integer. Listing 9.9 creates the HTML. For this example, we need only a single text field, but even so, we'll include a little PHP. Listing 9.9: An HTML Form That Calls Itself 1: <html> 2: <head> 3: <title>Listing 9.9 An HTML form that calls itself</title> 4: </head> 5: <body> 6: <form action="<?php print $PHP_SELF?>" method="POST"> 7: Type your guess here: <input type="text" name="guess"> 8: </form> 9: </body> 10: </html> Whatever we name the page that contains this form, the form always calls it argument. Note that we have not created a submit button. Most recent browsers will submit a form consisting of a single text field when the user hits the return key, but The script in Listing 9.9 will not produce any output. In Listing 9.10, we begin to build up the PHP element of the page. First, we need to define the number that the user will guess. In a fully working version, we would probably randomly generate this, but for now we will keep it simple. Next, we need to decide whether the form has been submitted; otherwise, we will attempt to assess variables that have not the variable $guess. $guess will have been made available as a global variable if yet been made available. We can test for submission by testing for the existence of you should be aware that some older browsers cannot do this. No your script has been sent a "guess" parameter. If this isn't present, we can safely assume that the user has arrived at the page without submitting a form. If the value is present, we can go ahead and test the value it contains. Listing 9.10: A PHP Number Guessing Script 1: <?php 2: $num_to_guess = 42; tf or co m er cia l, because we have assigned the value of $PHP_SELF to the FORM element's ACTION http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 164 3: $message = ""; 4: if ( ! isset( $guess ) ) 5: 6: 7: 9: 10: 11: 13: 14: 15: 17: 18: 19: 20: ?> 21: <html> 22: <head> 24: </head> 25: <body> 26: <h1> 28: </h1> { $message = "Welcome to the guessing machine!"; } ( $guess > $num_to_guess ) { $message = "$guess is too big! Try a smaller number"; } ( $guess < $num_to_guess ) { } { $message = "Well done!"; } 8: elseif 16: else // must be equivalent 23: <title>Listing 9.10 A PHP number guessing script</title> 29: <form action="<?php print $PHP_SELF?>" method="POST"> 30: Type your guess here: <input type="text" name="guess"> 31: </form> 33: </html> 32: </body> No The bulk of this script consists of an if statement that determines which string to assign to the variable $message. If the $guess variable has not been defined, we assume that the user has arrived for the first time and assign a welcome string the variable. Otherwise, we test the $guess variable against the number we have stored in $num_to_guess, and assign advice to $message accordingly. If $guess is neither larger nor smaller than $num_to_guess, we can assume that it is equivalent and tf or co m er 27: <?php print $message ?> cia l, http://i-tronics.blogspot.com/ us e fo re du ca $message = "$guess is too small! Try a larger number"; tio n 12: elseif on ly 165 assign a congratulations message to the variable. Now all we need to do is print the $message variable within the body of the HTML. There are a few more additions yet, but you can probably see how easy it would be to hand this page over to a designer. He can make it beautiful without having to disturb the programming in any way. Using Hidden Fields to Save State The script in Listing 9.10 has no way of knowing how many guesses a user has made. We can use a hidden field to keep track of this. A hidden field behaves exactly the source of the document that contains it. Listing 9.11 adds a hidden field to the Listing 9.11: Saving State with a Hidden Field 1: <?php 2: $num_to_guess = 42; 3: $message = ""; 5: if ( ! isset( $guess ) ) 6: 7: 8: 10: 11: 12: 14: 15: 16: 18: { } { } { } { 4: $num_tries = ( isset( $num_tries ) ) ? ++$num_tries : 0; $message = "$guess is too big! Try a smaller number"; ( $guess < $num_to_guess ) 13: elseif $message = "$guess is too small! Try a larger number"; 17: else // must be equivalent 19: No 20: 21: $guess = (int) $guess; 22: ?> 23: <html> 24: <head> 25: <title>Listing 9.11 Saving state with a hidden field</title> tf or $message = "Well done!"; } co m er cia l, 9: elseif ( $guess > $num_to_guess ) http://i-tronics.blogspot.com/ us $message = "Welcome to the guessing machine!"; e fo re du ca number guessing script and some PHP to work with it. tio n same as a text field, except that the user cannot see it, unless he views the HTML on ly 166 26: </head> 27: <body> 28: <h1> 29: <?php print $message ?> 30: </h1> 31: Guess number: <?php print $num_tries?> 32: <form action="<?php print $PHP_SELF?>" method="POST"> 33: Type your guess here: 34: <input type="text" name="guess" value="<?php print $guess?>"> 36: </form> 37: </body> 38: </html> The hidden field is given the name "num_tries". We also use PHP to write its value. While we're at it, we do the same for the "guess" field, so that the user can always see his last guess. This technique is useful for scripts that parse user input. If we were to reject a form submission for some reason we can at least allow our user to Tip When you need to output the value of an expression to the browser, you can of course use print() or echo(). When you are entering PHP mode explicitly PHP's short opening tags. If you add an equals (=) sign to the short PHP opening tag, the value contained will be printed to the browser. So is equivalent to <?=$test?> <? print $test;?> to output such a value you can also take advantage of a special extension to edit his previous query. Within the main PHP code, we use a ternary operator to increment the $num_tries variable. If the $num_tries variable is set, we add one to it and reassign this incremented value; otherwise, we initialize $num_tries to 0. Within the body of the HTML, we can now report to the user how many guesses he has made. No tf Caution Don't entirely trust hidden fields. You don't know where their values have been! This isn't to say that you shouldn't use them, just be aware that your users are capable of viewing and amending source code should they want to cheat your scripts. Use hidden fields for aesthetic reasons. They have no value as security features. or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n 35: <input type="hidden" name="num_tries" value="<?php print $num_tries?>"> on ly 167 Redirecting the User Our simple script still has one major drawback. The form is rewritten whether or not the user guesses correctly. The fact that the HTML is hard-coded makes it difficult to avoid writing the entire page. We can, however, redirect the user to a congratulations page, thereby sidestepping the issue altogether. When a server script communicates with a client, it must first send some headers that provide information about the document to follow. PHP usually handles this for you automatically, but you can choose to send your own header lines with PHP's header() function. To call the header() function, you must be sure that no output will send out headers and it will be too late for you to send your own. Any output cause headers to be sent. If you intend to use the header() function in a script you must make certain that nothing precedes the PHP code that contains the function call. You should also check any libraries that you might be using. Listing 9.12 shows typical headers sent to the browser by PHP. Example 9.12: Typical Server Headers Sent from a PHP Script 1: HEAD /matt/php-book/forms/eg9.1.php HTTP/1.0 3: Date: Sun, 09 Jan 2000 18:37:45 GMT 4: Server: Apache/1.3.9 (UNIX) PHP/4.0 6: Content-Type: text/html 5: Connection: close 2: HTTP/1.1 200 OK Connect to a Web host at port 80 and then type HEAD /path/to/file.html HTTP/1.0 followed by two returns. The headers should be displayed on your client. By sending a "Location" header instead of PHP's default, you can cause the browser to be redirected to a new page: Assuming that we have created a suitably upbeat page called "congrats.html", we can amend our number guessing script to redirect the user if she guesses correctly, as shown in Listing 9.13. Listing 9.13: Using header() to Send Raw Headers 1: <?php 2: $num_to_guess = 42; 3: $message = ""; header( "Location: http://www.corrosive.co.uk" ); No tf or co m er Tip You can see headers sent in response to a request by using a telnet client. cia l, http://i-tronics.blogspot.com/ us e fo re du ca from your document, even a line break or a space outside of your script tags will tio n has been sent to the browser. The first time that content is sent to the browser, PHP on ly 168 4: $num_tries = ( isset( $num_tries ) ) ? ++$num_tries : 0; 5: if ( ! isset( $guess ) ) 6: 7: 8: 10: 11: 12: 14: 15: 16: 18: 19: 20: 21: 23: ?> 24: <html> 25: <head> 27: </head> 28: <body> 29: <h1> 31: </h1> { $message = "Welcome to the guessing machine!"; } ( $guess > $num_to_guess ) { $message = "$num is too big! Try a smaller number"; } ( $guess < $num_to_guess ) { } { exit; } 9: elseif 17: else // must be equivalent header( "Location: congrats.html" ); 26: <title>Listing 9.13 Using header() to send raw headers</title> 30: <?php print $message ?> 32: Guess number: <?php print $num_tries?> 33: <form action="<?php print $PHP_SELF?>" method="POST"> 35: <input type="text" name="guess" value="<?php print $guess?>"> 36: <input type="hidden" name="num_tries" 37: value="<?php print $num_tries ?>"> 34: Type your guess here: No 38: </form> 39: </body> 40: </html> tf or co m er cia l, http://i-tronics.blogspot.com/ us e 22: $guess = (int) $guess; fo re du ca $message = "$num is too small! Try a larger number"; tio n 13: elseif on ly 169 The else clause of our if statement now causes the browser to download "congrats.html". We ensure that all output from the current page is aborted with the exit statement, which abruptly ends parsing and output, whether HTML or PHP. File Upload Forms and Scripts So far we've looked at simple form input. Browsers Netscape 2 or better and Internet Explorer 4 or better all support file uploads, and so, of course, does PHP4. this kind of input. include an ENCTYPE argument: ENCTYPE="multipart/form-data" In this section, you will examine the features that PHP makes available to deal with PHP also requires that a hidden field be included before the file upload field. This should be called MAX_FILE_SIZE and should have a value representing the maximum size in bytes of the file that you are willing to accept. This size cannot override the maximum size set in the upload_max_filesize field in your php.ini file that defaults to 2 megabytes. After the MAX_FILE_SIZE field has been entered, you are ready to add the upload field itself. This is simply an INPUT element with a TYPE together into an HTML upload form. 1: <html> 2: <head> 4: </head> 5: <body> 6: <form POST"> method=" argument of "file". You can give it any name you want. Listing 9.14 brings all this Listing 9.14: A Simple File Upload Form 3: <title>Listing 9.14 A simple file upload form</title> m er enctype="multipart/form-data" cia l, us e fo re du ca action="<?print 7: <input type="hidden" name="MAX_FILE_SIZE" value="51200"> No 10: </form> 12: </html> Notice that once again this form calls the page that contains it. This is because we are going to add some PHP code to handle the uploaded file. We limited file uploads 11: </body> tf 8: <input type="file" name="fupload"><br> 9: <input type="submit" value="upload!"> or co http://i-tronics.blogspot.com/ tio $PHP_SELF?>" n First, we need to create the HTML. HTML forms that include file upload fields must on ly 170 to 50KB and named our upload field "fupload". As you might expect, this name will soon become important. When a file is successfully uploaded, it is given a unique name and stored in a temporary directory (/tmp on UNIX systems). The full path to this file becomes available to you in a global variable with the same name as the file upload form field ($fupload in this case). PHP stores more information about the file for you in a series of global variables. These consist of the variable name (as derived from the form file Table 9.2 shows the meaning of these variables. Table 9.2: File Upload Global Variables Variable Name $fupload Contains Path temporary variable $fuploadname Name uploaded file $fuploadsize Example to /tmp/php5Pq3fU upload field) followed by an underscore character and "name", "size", and "type". of test.gif Size (in bytes) 6835 of uploaded file uploaded client) PHP4 also provides a new built-in variable that contains file upload information in $HTTP_POST_FILES array will be indexed by the names of each upload field in the form. The corresponding value for each of these keys will itself be an associative array. These fields are described in Table 9.3. Table 9.3: File Upload Global Variables Element or co m er array format. If one or more files has been uploaded via a form, the cia l, (where given by us $fupload type MIME type of image/gif file e $HTTP_POST_FILES[fupload][name] tf No $HTTP_POST_FILES[fupload][size] $HTTP_POST_FILES[fupload][type] http://i-tronics.blogspot.com/ fo re du ca Contains Name uploaded file Size (in bytes) 6835 of uploaded file MIME type of image/gif file Example of test.gif uploaded (where given by tio n on ly 171 client) Armed with this information, we can write a quick and dirty script that displays information about uploaded files (see Listing 9.15). If the uploaded file is in GIF format, the script will even attempt to display it. Listing 9.15: A File Upload Script 2: <head> 3: <title>Listing 9.15 A file upload script</title> 4: </head> 5: <?php 6: $file_dir = "/home/matt/htdocs/uploads"; 7: 8: if ( isset( $fupload ) ) 9: 10: 11: 12: 13: 14: 15: 17: 18: 19: 20: 21: ?> } } { print "path: $fupload<br>\n"; $file_url 1: <html> tio n { print "<img src=\"$file_url/$fupload_name\"><p>\n\n"; "http://80-www.corrosive.co.uk.proxy.lib.uiowa.edu/matt/uploads"; print "name: $fupload_name<br>\n"; print "type: $fupload_type<p>\n\n"; if ( $fupload_type == "image/gif" ) print "size: $fupload_size bytes<br>\n"; 22: <body> 24: <input type="hidden" name="MAX_FILE_SIZE" value="51200"> No 25: <input type="file" name="fupload"><br> x<input type="submit" value="Send file!"> 27: </form> 29: </html> In Listing 9.15, we first check to see whether the $fupload global variable exists. If 28: </body> tf or 23: <form enctype="multipart/form-data" action="<?php print $PHP_SELF?>" method="POST"> co m er cia l, 16: copy ( $fupload, "$file_dir/$fupload_name") or die ("Couldn't copy"); http://i-tronics.blogspot.com/ us e fo re du ca on ly = 172 it does, we can assume that a file upload exists (at least for the purposes of this exercise). Caution Never assume that data sent to your scripts originates from a particular source or that a request contains the type and range of data that your script was designed to accept. In Listing 9.15, we make the assumption that a particular variable derives its name from a form upload field. In fact, there is nothing to stop a mischievous user from creating her own form that sends data to our script. She could easily send our script a parameter with the same name as our form upload If this sounds paranoid, it is meant to. Paranoia is a good thing in external source, even if that source seems to be a form that you have created. If a file has been uploaded, the path to the uploaded file on the server is contained in the variable $fupload, and we print this to the browser. We also print the filename, which is stored in $fupload_name, the file's size, which is stored in $fupload_size, and the file's MIME type, which is stored in $fupload_type. We then test the value contained by $fupload_type. If this is "image/gif", we ignoring case, and you will see how to do this in Hour 17, "Working with Strings." altogether was named with a ".gif" extension, but let's ease off on the caution for now. If we are dealing with a GIF image, we use the copy() function to copy the uploaded file from its default location to a directory in our server space. The copy() function requires two string arguments; the original and new paths to a file. It returns true if the copy is successful. The original path to our file is stored in $fupload. We have created a variable $file_dir that contains the full path to the directory we want to use to store uploaded images. This, combined with the file's name as stored in function call, the uploaded file should be copied to our upload directory with its original name restored. Note that on UNIX systems server scripts run as a special user, often 'nobody'. Before you copy a file to a directory you should make sure that your process is allowed to do so. We are using the or operator and the die() function to abort the script if copying fails. We will cover this technique in more detail in Hour 10, "Working with Files." Having copied the file, we do not need to delete the original. PHP will handle this for $fupload_name, forms the second argument passed to copy(). As a result of this No tf or co m er cia l, Our assumption here also glosses over the possibility that another kind of file http://i-tronics.blogspot.com/ us assume that we are dealing with a GIF. In fact, it would be a good idea to test this e fo re du ca server-side Web programming. Never trust data that comes from an tio n file but with plain text content. on ly 173 us. When we created the $file_dir variable to store the file path to our upload directory, we also created a variable called $file_url to store the URL of the same directory. We wrap up the script by writing an HTML image element that references our newly written image. Summary missing, of course. Now that you can get information from the user, it would be nice to be able to do something with it. Write it to a file, perhaps. That is the subject of the next hour. Throughout this hour, you have learned how to work with the $GLOBALS associative array and acquire environment variables, form input, and uploaded files using global variables. You have also learned how to send raw headers to the client to redirect a browser. You have learned how to acquire list information from form fields. submissions and how to pass information from script call to script call using hidden Q Can I create arrays for values entered into elements other than select and check box fields? A Yes, in fact any element name ending with empty square brackets in a form will resolve to an array element when the form is submitted. You can use this fact to Q The header() function seems powerful. Will we look at HTTP headers in more detail? A We cover HTTP (Hypertext Transfer Protocol) in more detail in Hour 13, "Beyond Q Automatically converting form element names into variables seems a little risky. Can I disable this feature? A Yes, you can ensure that submitted form element names are not converted into global variables by setting the gpc_globals directive to "off" in the php.ini file. group values submitted from multiple fields of any type into an array. No Workshop tf the Box." or co m er cia l, Q&A http://i-tronics.blogspot.com/ us e fo re du ca tio create truly sophisticated and interactive environments. There are still a few things n If you've kept up so far, things should be getting exciting now. You have the tools to on ly 174 The Workshop provides quiz questions to help you solidify your understanding of the material covered. Try to understand the quiz answers before continuing to the next hour's lesson. Quiz answers are provided in Appendix A. Quiz Which environment variable could you use to determine the IP address of a user? Which environment variable could you use to find out about the browser that called your script? array variable called $form_array? request? request? would you pass it? form? Which built-in associative array contains all values submitted as part of a POST What function would you use to redirect the browser to a new page? What string How must you limit the size of a file that a user can submit via a particular upload How can you set a limit to the size of upload files for all forms and scripts? Activities Create a calculator script that allows the user to submit two numbers and choose Use hidden fields with the script you created in activity 1 to store and display the number of requests that the user has submitted. No tf or co m er an operation to perform on them (addition, multiplication, division, subtraction). cia l, http://i-tronics.blogspot.com/ us e fo re du ca Which built-in associative array contains all values submitted as part of a GET tio n What should you name your form fields to access their submitted values from an on ly 175 Hour 10: Working with Files Overview Testing, reading, and writing to files are staple activities f or any full-featured programming language. PHP is no exception, providing you with functions that make the process straightforward. In this hour, you will learn How to include files in your documents How to test files and directories How to open a file before working with it How to read data from files How to write or append to a file How to lock a file How to work with directories PHP code in these files can be executed as if it were part of the main document. This can be useful for including library code in multiple pages. it into every document that needs to use it. Of course, if you discover a bug, or want to add a feature, you will have to find every page that uses the function to make the change. The include() statement can save you from this chore. You can add the function to a single document and, at runtime, read this into any page that needs it. co The include() function requires a single argument, a relative path to the file to be included. Listing 10.1 creates a simple PHP script that uses Listing 10.1: Using include() m er cia l, Having created a killer function, your only option until now would have been to paste us e Including Files with include() The include() function enables you to incorporate files into your PHP documents. fo re du ca tio include() to No tf 1: <html> 2: <head> 3: <title>Listing 10.1 Using include()</title> 4: </head> 5: <body> 6: <?php 7: include("eg10.2.php"); 8: ?> or incorporate and output the contents of a file. http://i-tronics.blogspot.com/ n on ly 176 9: </body> 10: </html> include() statement in Listing 10.1 incorporates the document eg10.2.php, the contents of which you can see in Listing 10.2. When run, Listing 10.1 outputs the string "I have been included!!", which may seem strange, The given that we have included plain text within a block of PHP code. Shouldn't this cause an error? In fact, the contents of an included file are displayed as HTML by default. If you want to execute PHP code in an included file, you must enclose it in PHP start and end tags. In Listings 10.3 and 10.4, we amend the previous example Example 10.2: The File Included in Listing 10.1 1: I have been included!! Listing 10.3: Using the include() Function to Execute PHP in Another File 1: <html> 2: <head> 4: </head> 5: <body> 6: <?php 7: include("eg10.4.php"); 8: ?> 9: </body> 10: </html> 1: <?php 3: <title>Listing 10.3 Using include to execute PHP in another file</title> 2: print "I have been included!!<BR>"; 3: print "But now I can add up... 4: ?> co m er Listing 10.4: An Include File Containing PHP Code tf Included files in PHP4 can return a value in the same way as functions do. As in a or No function, using the return included file. Additionally, no further HTML will be included. In Listings 10.5 and Listing 10.5: Using include() to Execute PHP and Assign the Return Value 1: <html> 2: <head> 3: <title>Listing 10.5 Using include() to execute PHP and assign the return 10.6, we include a file, assigning its return value to a variable. cia l, statement ends the execution of code within the http://i-tronics.blogspot.com/ us 4 + 4 = ".(4 + 4); e fo re du ca tio n so that code is executed in the included file. on ly 177 Avalue</title> 4: </head> 5: <body> 6: <?php 7: $addResult = include("eg10.6.php"); 8: print "The include file returned $addResult"; 9: ?> 10: </body> 11: </html> Listing 10.6: An Include File That Returns a Value 1: <?php 2: $retval = ( 4 + 4 ); 3: return $retval; 4: ?> 5: This HTML should never be displayed because it comes after a return statement! Note Returning values from included files would only work in PHP3 if the return an error. You can use an cia l, include() us statement was contained in a function. The code in Listing 10.6 would cause statement in a conditional statement, and the e referenced file will only be read if the condition is met. The in the following fragment will never be called, for example if ( $test ) { } include( "a_file.txt" ); // won't be included If you use an or co m er $test = false; include() statement within a loop, it will be replaced with the No content will be executed for every call. Listing 10.7 illustrates this by using an statement in a include() tf contents of the referenced file each time the for loop. The different file for each iteration. 1: <html> 2: <head> 3: <title>Listing 10.7 Using include() within a loop</title> Listing 10.7: Using include() Within a Loop http://i-tronics.blogspot.com/ fo re du ca include() include() statement include() statement is called. This statement references a tio n on ly 178 4: </head> 5: <body> 6: <?php 7: for ( $x = 1; $x<=3; $x++ ) 8: 9: 10: 11: 12: 13: 14: ?> 15: </body> 16: </html> { $incfile = "incfile$x".".txt"; print "Attempting include $incfile<br>"; include( "$incfile" ); print "<p>"; } When Listing 10.7 is run, it includes the content of three different files, "incfile1.txt", "incfile2.txt", something like this: This is incfile1.txt Attempting to include incfile2.txt This is incfile2.txt Attempting to include incfile3.txt and these files simply contains a confirmation of its own name, the output should look Note PHP also has a require() statement, which performs a similar function. As of PHP4, you can include a require() statement in a loop as you can with a value, however. include(). A file included as a result of a require() statement cannot return Testing Files it. PHP4 provides many functions that help you to discover information about files No on your system. This section briefly covers some of the most useful. tf Before you work with a file or directory, it is often a good idea to learn more about or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca "incfile3.txt". Assuming that each of tio n on ly 179 Checking for Existence with file_exists() You can test for the existence of a file with the file_exists() function. This requires a string representing an absolute or relative path to a file that may or may not be there. If the file is found, it returns true; otherwise, it returns false. if ( file_exists("test.txt") ) print "The file exists!"; A File or a Directory? You can confirm that the entity you are testing is a file, as opposed to a directory, with the is_file() function. is_file() requires the file path and returns a Boolean value: if ( is_file( "test.txt" ) ) print "test.txt is a file!"; You can do this with the is_dir() function. is_dir() requires the path to the directory if ( is_dir( "/tmp" ) ) print "/tmp is a directory"; Checking the Status of a File When you know that a file exists, and it is what you expect it to be, you can then find out some things that you can do with it. Typically, you might want to read, write to, or execute a file. PHP can help you with all of these. No is_readable() tells you whether you can read a file. On UNIX systems, you may be able to see a file but still be barred from reading its contents. is_readable() accepts the file path as a string and returns a Boolean value: if ( is_readable( "test.txt" ) ) print "test.txt is readable"; tf or co m er cia l, and returns a Boolean value: http://i-tronics.blogspot.com/ us Conversely, you might want to check that the entity you are testing is a directory. e fo re du ca tio n on ly 180 is_writable() tells you whether you can write to a file. Once again it requires the file path and returns a Boolean value: if ( is_writable( "test.txt" ) ) print "test.txt is writable"; is_executable() tells you whether you can run a file, relying on either the file's permissions or its extension depending on your platform. It accepts the file path and returns a Boolean value: if ( is_executable( "test.txt" ) print "test.txt is executable"; Determining File Size with filesize() Given the path to a file, filesize() attempts to determine and return its size in bytes. It returns false if it encounters problems. print "The size of test.txt is.. "; print filesize( "test.txt" ); Getting Date Information About a File Sometimes you will need to know when a file was last written to or accessed. PHP provides several functions that can provide this information. You can find out when a file was last accessed with fileatime(). This function requires the file path and returns the date that the file was last accessed. To access a file means either to read or write to it. Dates are returned from all these functions in UNIX epoch format. That is, the number of seconds since 1 January 1970. In our examples, we use the date() function to translate this into human readable form. You learn more about date functions in Hour 15, "Working with Dates." No $atime = fileatime( "test.txt" ); print "test.txt was last accessed on "; print date("D d M Y g:i A", $atime); // Sample output: Thu 13 Jan 2000 2:26 PM tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 181 You can discover the modification date of a file with the function filemtime(), which requires the file path and returns the date in UNIX epoch format. To modify a file means to change its contents in some way. $mtime = filemtime( "test.txt" ); print "test.txt was last modified on "; print date("D d M Y g:i A", $mtime); // Sample output: Thu 13 Jan 2000 2:26 PM] modified or changes are made to its permissions or ownership. On other platforms, the filectime() returns the creation date. $ctime = filectime( "test.txt" ); print "test.txt was last changed on "; print date("D d M Y g:i A", $ctime); // Sample output: Thu 13 Jan 2000 2:26 PM] together into one script. Listing 10.8: A Function to Output the Results of Multiple File Tests 1: <html> 2: <head> 3: <title>Listing 10.8 A function to output the results of multiple file tests</ No 10: tf 4: </head> 5: <body> 6: <?php 7: $file = "test.txt"; 8: outputFileTestInfo( $file ); 9: function outputFileTestInfo( $f ) { or title> co m er cia l, Listing 10.8 creates a function that brings the file test functions we have looked at http://i-tronics.blogspot.com/ us Creating a Function That Performs Multiple File Tests e fo re du ca tio function. On UNIX systems, the change time is set when a file's contents are n PHP also allows you to test the change time of a document with the filectime() on ly 182 11: 12: 13: 14: 15: 16: 17: 18: 19: 20: 21: 22: 23: 24: 25: 26: 27: ?> 28: </body> 29: </html> if ( ! file_exists( $f ) ) { print "$f does not exist<BR>"; return; } print "$f is ".(is_file( $f )?"":"not ")."a file<br>"; print "$f is ".(is_dir( $f )?"":"not ")."a directory<br>"; print "$f is ".(is_readable( $f )?"":"not ")."readable<br>"; print "$f is ".(is_writable( $f )?"":"not ")."writable<br>"; print "$f is ".(filesize($f))." bytes<br>"; print "$f was accessed on ".date( "D d M Y g:i A", fileatime( $f ) )."<br>"; print "$f was modified on ".date( "D d M Y g:i A", filemtime( $f ) )."<br>"; print "$f was changed on ".date( "D d M Y g:i A", filectime( $f ) )."<br>"; } Notice that we have used the ternary operator as a compact way of working with print "$f is ".(is_file( $f )?"":"not ")."a file<br>"; We use the is_file() function as the right-hand expression of the ternary operator. If this returns true, an empty string is returned. Otherwise, the string "not " is returned. The return value of the ternary expression is added to the string to be printed with concatenation operators. This statement could be made clearer but less scompact, as follows: $is_it = is_file( $f )?"":"not "; print "$f is $isit"."a file"; No tf or co some of these tests. Let's look at one of these in more detail: m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca print "$f is ".(is_executable( $f )?"":"not ")."executable<br>"; tio n on ly 183 We could, of course, be even clearer with an if statement, but imagine how large the function would become if we had used the following: if ( is_file( $f ) ) print "$fi is a file<br>"; else print "$fi is not a file<br>"; Because the result of these three approaches is the same, the approach you take If a file does not yet exist, you can create one with the touch() function. Given a string representing a file path, touch() attempts to create an empty file of that name. If the file already exists, the contents are not disturbed, but the modification date is updated to the time at which the function executed. touch("myfile.txt"); accepts a file path: unlink("myfile.txt"); All functions that create, delete, read, write, or modify files on UNIX systems require PHP provides the fopen() function for this. fopen() requires a string containing the file path, followed by a string containing the mode in which the file is to be opened. No The most common modes are read ('r'), write ('w'), and append ('a'). fopen() returns an integer you will later use to work with the open file. This integer is known as a file pointer and should be assigned to a variable. To open a file for reading, you would use the following: $fp = fopen( "test.txt", 'r' ); You would use the following to open a file for writing: tf or Before you can work with a file, you must first open it for reading, writing, or both. co Opening a File for Writing, Reading, or Appending m er that the correct file or directory permissions are set. cia l, http://i-tronics.blogspot.com/ us You can remove an existing file with the unlink() function. Once again, unlink() e fo re du ca Creating and Deleting Files tio n becomes broadly a matter of preference. on ly 184 $fp = fopen( "test.txt", 'w' ); To open a file for appending (that is, to add data to the end of a file), you would use this: $fp = fopen( "test.txt", 'a' ); therefore, to test the function's return value before proceeding to work with it. You can do this with an if statement: if ( $fp = fopen( "test.txt", "w" ) ) { // do something with $fp } Or you can use a logical operator to end execution if an essential file can't be opened: ( $fp = fopen( "test.txt", "w" ) ) or die ("Couldn't open file, sorry"); never be reached. Otherwise, the right-hand side of the or operator will be parsed, Assuming that all is well and you go on to work with your open file, you should which requires the file pointer returned from a successful fopen() call as its argument: fclose( $fp ); No PHP provides a number of functions for reading data from files. These enable you to read by the byte, the line, or even the character. tf Reading from Files or co m er remember to close it when you have finished. You can do this by calling fclose(), cia l, and the die() function will be called. http://i-tronics.blogspot.com/ us the die() function (which writes a message to the browser and ends the script) will e If the fopen() function returns true, the rest of the expression won't be parsed, and fo re du ca tio n on ly fopen() returns false if the file cannot be opened for any reason. It is a good idea, 185 Reading Lines from a File with fgets() and feof() After you have opened a file for reading, you will often need to access it line by line. To read a line from an open file, you can use fgets(), which requires the file pointer argument. This specifies the number of bytes the function should read if it doesn't returned from fopen() as an argument. You must also pass it an integer as a second first encounter a line end or the end of the file. The fgets() function reads the file length argument, or the end of the file. Although you can read lines with fgets(), you need some way of telling when you have reached the end of the file. The feof() function does this, returning true when the end of the file has been reached and false otherwise. Once again this function requires a file pointer as its argument: feof( $fp ); // where $fp is the file pointer returned by fopen() Listing 10.9: Opening and Reading a File Line by Line 1: <html> 2: <head> 3: <title>Listing 10.9 Opening and reading a file line by line</title> 4: </head> 5: <body> 6: <?php 8: $fp = fopen( $filename, "r" ) or die("Couldn't open $filename"); No 10: 11: 12: 13: 14: ?> tf 9: while ( ! feof( $fp ) ) { $line = fgets( $fp, 1024 ); print "$line<br>"; } or 7: $filename = "test.txt"; co m er cia l, http://i-tronics.blogspot.com/ us e You now have enough information to read a file line by line, as shown in Listing 10.9. fo re du ca $line = fgets( $fp, 1024 ); // where $fp is the file pointer returned by fopen() tio n until it reaches a newline character ("\n"), the number of bytes specified in the on ly 186 15: </body> 16: </html> We call fopen() with the name of the file that we want to read, using the or operator to ensure that script execution ends if the file cannot be read. This usually occurs if the file does not exist, or (on a UNIX system) if the file's permissions won't allow the The while statement's test expression calls feof() for each iteration, ending the loop script read access to the file. The actual reading takes place in the while statement. when it returns true. In other words, the loop continues until the end of the file is the file. We assign the result to $line and then print it to the browser, appending a <BR> tag for the sake of readability. Reading Arbitrary Amounts of Data from a File with fread() Rather than reading text by the line, you can choose to read a file in arbitrarily defined chunks. The fread() function accepts a file pointer as an argument, as well as the number of bytes you want to read. It returns the amount of data you have requested unless the end of the file is reached first. Listing 10.10 amends our previous example so that it reads data in chunks of 16 bytes rather than by the line. Listing 10.10: Reading a File with fread() 1: <html> 2: <head> 3: <title>Listing 10.10 Reading a file with fread()</title> 4: </head> No 10: tf 5: <body> 6: <?php 7: $filename = "test.txt"; 8: $fp = fopen( $filename, "r" ) or die("Couldn't open $filename"); 9: while ( ! feof( $fp ) ) { or co m er cia l, $chunk = fread( $fp, 16 ); http://i-tronics.blogspot.com/ us e fo re du ca tio reached. Within the code block, we use fgets() to extract a line (or 1024 bytes) of n on ly 187 11: 12: 13: 14: ?> 15: </body> 16: </html> $chunk = fread( $fp, 16 ); print "$chunk<br>"; } won't let you decide the position from which the acquisition begins. You can set this position within a file. It requires a file pointer and an integer representing the offset from the start of the file (in bytes) to which you want to jump: fseek( $fp, 64 ); Listing 10.11 uses fseek() and fread() to output the second half of a file to the browser. Listing 10.11: Moving Around a File with fseek() 2: <head> 3: <title>Listing 10.11 Moving around a file with fseek()</title> 4: </head> 5: <body> 6: <?php 8: $fp = fopen( $filename, "r" ) or die("Couldn't open $filename"); 9: $fsize = filesize($filename); 10: $halfway = (int)( $fsize / 2 ); No 11: print "Halfway point: $halfway <BR>\n"; 12: fseek( $fp, $halfway ); 13: $chunk = fread( $fp, ($fsize − $halfway) ); 14: print $chunk; 15: ?> tf or co 7: $filename = "test.txt"; m er cia l, http://i-tronics.blogspot.com/ us 1: <html> e fo re du ca manually with the fseek() function. fseek() enables you to change your current tio n Although fread() allows you to define the amount of data acquired from a file, it on ly 188 16: </body> 17: </html> We calculate the halfway point of our file by dividing the return value of filesize() by 2. We can then use this as the second argument to fseek(), jumping to the halfway point. Finally, we call fread() to extract the second half of the file, printing the result to the browser. Reading Characters from a File with fgetc() every time it is called. Because a character is always 1 byte in size, fgetc() doesn't require a length argument. You simply need to pass it a file pointer: $char = fgetc( $fp ); Listing 10.12 creates a loop that reads the file "test.txt" a character at a time, outputting each character to the browser on its own line. Listing 10.12: Moving Around a File with fseek() 1: <html> 2: <head> 3: <title>Listing 10.12 Moving around a file with fseek()</title> 4: </head> 5: <body> 6: <?php 7: $filename = "test.txt"; No 10: 11: 12: 13: 14: ?> 15: </body> tf 9: while ( ! feof( $fp ) ) { or 8: $fp = fopen( $filename, "r" ) or die("Couldn't open $filename"); $char = fgetc( $fp ); print "$char<BR>"; } co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca fgetc() is similar to fgets() except that it returns only a single character from a file tio n on ly 189 16: </html> Writing or Appending to a File The processes for writing to or appending to a file are the same. The difference lies when you call fopen(): $fp = fopen( "test.txt", "w" ); exist, it will be created. If the file already exists, any prior content will be destroyed When you append to a file, you should use mode "a" in your fopen() call: $fp = fopen( "test.txt", "a" ); Any subsequent writes to your file are added to the existing content. Writing to a File with fwrite() or fputs() fwrite() accepts a file pointer and a string. It then writes the string to the file. fputs() works in exactly the same way. fwrite( $fp, "hello world" ); fputs( $fp, "hello world" ); Writing to files is as straightforward as that. Listing 10.13 uses fwrite() to print to a Listing 10.13: Writing and Appending to a File 1: <html> No tf 2: <head> 3: <title>Listing 10.13 Writing and appending to a file</title> 4: </head> 5: <body> 6: <?php 7: $filename = "test.txt"; 8: print "Writing to $filename<br>"; or co file. We then append a further string to the same file using fputs(). m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca and replaced by the data you write. tio All subsequent writing will occur from the start of the file. If the file doesn't already n on ly in the fopen() call. When you write to a file, you should use the mode argument "w" 190 9: $fp = fopen( $filename, "w" ) or die("Couldn't open $filename"); 10: fwrite( $fp, "Hello world\n" ); 11: fclose( $fp ); 12: print "Appending to $filename<br>"; 13: $fp = fopen( $filename, "a" ) or die("Couldn't open $filename"); 14: fputs( $fp, "And another thing\n" ); 15: fclose( $fp ); 16: ?> 17: </body> 18: </html> Locking Files with flock() The techniques you have learned for reading and amending files will work fine if you would expect many users to access your projects more or less at the same time. Imagine what would happen if two users were to execute a script that writes to one file at the same moment. The file will quickly become corrupt. PHP4 provides the flock() function to forestall this eventuality. flock() will lock a file process is working with it. flock() requires a valid file pointer, and an integer representing the kind of lock you would like to set. In Table 10.1 we list three kinds Table 10.1: Integer Arguments to the flock() Function Integer 1 of locks you can apply to a file. or co m er to warn other process against writing to or reading from a file while the current cia l, us e are only presenting your script to a single user. In the real world, however, you tf fo re du ca Lock Type Shared tio Description Allows processes prevents writing file) (used when reading a other to read the file but http://i-tronics.blogspot.com/ No n on ly 191 2 Exclusive Prevents other processes from either reading from or writing to a file (used a file) when writing to 3 Release Releases shared You should call flock() directly after calling fopen() and then call it again to release the lock before closing the file. $fp = fopen( "test.txt", "a" ); flock( $fp, 2 ); // exclusive lock // write to the file flock( $fp, 1 ); // release the lock fclose( $fp ); Caution Locking with flock() is advisory. Only other scripts that use flock() Now that you can test, read, and write to files, turn your attention to directories. remove, and read them. Creating Directories with mkdir() No mkdir() enables you to create a directory. mkdir() requires a string representing the path to the directory you want to create and an integer that should be an octal number representing the mode you want to set for the directory. You specify an octal (base 8) number with a leading 0. The mode argument will only have an effect on UNIX systems. The mode should consist of three numbers between 0 and 7, representing permissions for the directory owner, group, and everyone, tf or co PHP provides many functions to work with directories. You will look at how to create, m er Working with Directories cia l, will respect a lock that you set. http://i-tronics.blogspot.com/ us e fo re du ca tio exclusive lock n on ly a or 192 respectively. This function returns true if it successfully creates a directory, or false if it doesn't. If mkdir() fails, this will usually be because the containing directory has permissions that preclude processes with the script's user ID from writing. mkdir( "testdir", 0777 ); // global read/write/execute permissions Removing a Directory with rmdir() rmdir() enables you to remove a directory from the file system, if the process Opening a Directory for Reading with opendir() Before you can read the contents of a directory, you must first obtain a directory pointer. You can do this with the opendir() function. opendir() requires a string representing the path to the directory you want to open. opendir() returns a returns false. $dh = opendir( "testdir" ); directory handle unless the directory is not present or readable, in which case it Reading the Contents of a Directory with readdir() Just as you use gets() to read a line from a file, you can use readdir() to read a file returns a string containing the item name. If the end of the directory has been items, rather than full paths. Listing 10.14 shows the contents of a directory. Listing 10.14: Listing the Contents of a Directory with readdir() No tf 1: <html> 2: <head> 3: <title>Listing 10.14 Listing the contents 4: of a directory with readdir()</title> 5: </head> or reached, readdir() returns false. Note that readdir() returns only the names of its co or directory name from a directory. readdir() requires a directory handle and m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca rmdir( "testdir" ); tio requires only a string representing the path to the directory you want to create. n running your script has the right to do so, and if the directory is empty. rmdir() on ly 193 6: <body> 7: <?php 8: $dirname = "testdir"; 9: $dh = opendir( $dirname ); 10: while ( gettype( $file = readdir( $dh )) != boolean ) 11: 12: 13: 14: 15: { if ( is_dir( "$dirname/$file" ) ) print "(D)"; print "$file<br>"; } 16: closedir( $dh ); 17: ?> 18: </body> 19: </html> statement to loop through each of its elements. We call readdir() as part of the while body of the while statement, we use the $dirname variable in conjunction with the $file variable to create a full file path, which we can then test. If the path leads to a We have used a cautious construction in the test of the while statement. Most PHP while ( $file = readdir( $dh ) ) No The value returned by readdir() will be tested. Because any string other than "0" will resolve to true, there should be no problem. Imagine, however, a directory that contains four files, "0", "1", "2", and "3". The output from the preceding code on my system is as follows: tf or { print "$file<BR>\n"; } co programmers (myself included) would use something like the following: m er directory, we print "(D)" to the browser. Finally, we print the filename. cia l, statement's test expression, assigning its result to the $file variable. Within the http://i-tronics.blogspot.com/ us We open our directory for reading with the opendir() function and use a while e fo re du ca tio n on ly 194 When the loop reaches the file named "0", the string returned by readdir() resolves to false, causing the loop to end. The approach in Listing 10.14 tests the type of the value returned by the readdir() function, thus circumventing the problem. Summary In this hour, you learned how to use include() to incorporate files into your documents and to execute any PHP code contained in include files. You learned how to use some of PHP's file test functions. You explored functions for reading files by either replacing or appending to existing content. Finally, you learned how to create, remove, and read directories. Q&A Q Will the include() function slow down my scripts? some overhead. The effect should be negligible, however. writing or reading? A Because an included file must be opened and parsed by the interpreter, it will add Q Should I always end script execution if a file cannot be opened for A You should always allow for this possibility. If your script absolutely depends on the file you want to work with, you might want to use the die() function, writing an informative error message to the browser. In less critical situations, you will still need to allow for the failure, perhaps adding it to a log file. You can read more about logging in Hour 22, "Debugging." The Workshop provides quiz questions to help you solidify your understanding of the material covered. Try to understand the quiz answers before continuing to the next hour's lesson. Quiz answers are provided in Appendix A. No Quiz tf What functions could you use to add library code to the currently running script? What function would you use to find out whether a file is present on your file system? How would you determine the size of a file? or co Workshop m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio the line, by the character, or in arbitrary chunks. You learned how to write to files, n on ly 195 What function would you use to open a file for reading or writing? What function would you use to read a line of data from a file? How can you tell when you have reached the end of a file? What function would you use to write a line of data to a file? How would you open a directory for reading? What function would you use to read the name of a directory item after you have opened a directory for reading? Activities Create a form that accepts a user's first and second name. Create a script that Create a script that reads the data file you created in activity 1. As well as writing its contents to the browser (adding a <BR> tag to each line), print a summary that includes the number of lines in the file and the file's size. No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca saves this data to a file. tio n on ly 196 Hour 11: Working with the DBM Overview If you don't have access to a SQL database such as MySQL or Oracle, you will almost certainly have a DBM-style database system available to you. Even if you don't have the DBM functions allow you to store and manipulate name/value pairs on your system. such a library on your system, PHP can emulate the functionality for you. Essentially, Although these functions do not offer you the power of a SQL database, they are flexible and easy to use. Because the format is so common, code written to take advantage of these functions is likely to be portable, although the DBM files themselves might not be. In this hour, you will learn How to open a DBM database How to extract data from the database How to change and delete items How to store more complex kinds of data in DBM databases You can open a DBM database with the function dbmopen(). This function requires you want to open the database. dbmopen() returns a special DBM identifier that you can then pass to other DBM functions to access or manipulate your database. Because dbmopen() involves reading from and writing to files, PHP must have No permission to write to the directory that will contain your database. The flags that you pass to dbmopen() determine the way in which you can work with your database. They are listed in Table 11.1 Table 11.1: Flags for Use with dbmopen() Flag Description tf or two arguments: the path to a DBM file and a string containing the flags with which co Opening a DBM Database m er cia l, How to add data to the database http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly Functions 197 r Open database reading only w Open database for writing reading and (or open for read/write access if it exists) n Create database (truncate new The following code fragment opens a database, creating a new one if it does not already exist: $dbh = dbmopen( "./data/products", "c" ) or die( "Couldn't open DBM" ); Notice that we use a die() statement to end script execution if our attempt to open When you finish working with a database, close it using the function dbmclose(). This is because PHP locks a database that you are working with so that other close the database, then other processes are going to have to wait longer before getting their bite of the cherry. dbmclose() requires a valid DBM identifier: dbmclose ( $dbh ); processes cannot attempt to modify the data you are reading or writing. If you don't the database fails. Adding Data to the Database You can add name/value pairs to your open database with the function dbminsert(), which requires a valid DBM identifier (as returned by dbmopen()), the name of a key, element already exists in the database, and − 1 if an error occurs (such as an attempt to write to a database opened in read-only mode). If the element you are No attempting to insert already exists, then the data is not overwritten. Listing 11.1 creates or opens a database called products and adds some data to it. Listing 11.1: Adding Items to a DBM Database 1: <html> 2: <head> 3: <title>Listing 11.1 Adding items to a DBM database</title> 4: </head> http://i-tronics.blogspot.com/ tf or and the value that you want to store. This function returns 0 if all is well, 1 if the co m er cia l, us e fo re du ca old version if it exists) tio n on ly c Create database 198 5: <body> 6: Adding products now... 7: 8: <?php 9: $dbh = dbmopen( "./data/products", "c" ) or die( "Couldn't open DBM" ); 10: 11: dbminsert( $dbh, "Sonic Screwdriver", "23.20" ); 12: dbminsert( $dbh, "Tricorder", "55.50" ); 13: dbminsert( $dbh, "ORAC AI", "2200.50" ); 14: dbminsert( $dbh, "HAL 2000", "4500.50" ); 15: 16: dbmclose( $dbh ); 17: ?> 18: </body> 19: </html> All values are converted to strings when added to the database, so we add quotes to the product prices to maintain their format. We can treat these strings as doubles keys that have more than one word. when we extract them from the database if we need to. Notice also that we can use If we now attempt to call dbminsert() with the same key argument as one of the database. In some circumstances, this might be what you want, but in others, you will want to amend existing data, as well as create new elements. Amending Elements in a Database You can amend an entry in a DBM database with the dbmreplace() function. dbmreplace() requires a valid DBM identifier, the name of a key, and the new value to add. It returns 0 if all goes well and − 1 if an error occurs. Listing 11.2 amends the code in Listing 11.1 so that keys are added regardless of existence. Listing 11.2: Adding or Changing Items to a DBM Database No tf 1: <html> 2: <head> 4: </head> 5: <body> 6: Adding products now... 7: <?php 3: <title>Listing 11.2 Adding or changing items to a DBM database</title> or co m er cia l, keys we have already used, dbminsert() returns 1 and makes no change to the http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 199 8: $dbh = dbmopen( "./data/products", "c" ) 9: or die( "Couldn't open DBM" ); 10: dbmreplace( $dbh, "Sonic Screwdriver", "25.20" ); 11: dbmreplace( $dbh, "Tricorder", "56.50" ); 12: dbmreplace( $dbh, "ORAC AI", "2209.50" ); 13: dbmreplace( $dbh, "HAL 2000", "4535.50" ); 14: dbmclose( $dbh ); 15: ?> 16: </body> 17: </html> change the functionality of the script. Reading from a DBM Database Now that we can add data to our database, we need to find a way to fetch it. We can extract an individual element from the database with the dbmfetch() function. dbmfetch() requires a valid DBM identifier and the name of the element you want to the price of the "Tricorder" item, we would use the following code: $price = dbmfetch( $dbh, "Tricorde" ); an empty string. If the "Tricorder" element does not exist in the database, then dbmfetch() returns You won't always know the names of all the keys in the database, however. What hard-coding the product names into your script? PHP provides a mechanism by which you can loop through every element in a database. You can get the first key in a database with the dbmfirstkey() function. This requires a DBM identifier and returns the first key. Note that this won't necessarily be the first element that you added because DBM databases often maintain their own subsequent key with the dbmnextkey() function. Once again dbmnextkey() ordering systems. After you've retrieved the first key, you can access each access. The function returns the value you are accessing as a string. So to access No requires a DBM identifier and returns an element's key. By combining these functions with dbmfetch(), you can now list an entire database. Listing 11.3 outputs the products database to the browser. Listing 11.3: Reading All Records from a DBM Database 1: <html> 2: <head> tf or co m er would you do if you needed to output every product and price to the browser without cia l, http://i-tronics.blogspot.com/ us e fo re du ca We have only had to change the function calls from dbminsert() to dbmreplace() to tio n on ly 200 3: <title>Listing 11.3 Reading all 4: records from a DBM Database </title> 5: </head> 6: <body> 7: Here at the Impossible Gadget Shop 8: 9: we're offering the following exciting products: 10: <p> 11: <table border=1 cellpadding ="5"> 12: <tr> 13: <td align="center"> <b>product</b></td> 14: <td align="center"> <b>price</b> </td> 15: </tr> 16: <?php 18: 17: $dbh = dbmopen( "./data/products", "c" ) or die( "Couldn't open DBM" ); 19: $key = dbmfirstkey( $dbh ); 20: while ( $key != "" ) 21: 22: 23: 24: 25: 26: 28: ?> 29: </table> 30: </body> 31: </html> { print "<tr><td align = \"left\"> $key </td>"; $key = dbmnextkey( $dbh, $key ); } No tf Figure 11.1 shows the output from Listing 11.3. or co m er 27: dbmclose( $dbh); cia l, print "<td align = \"right\"> \$$value </td></tr>"; http://i-tronics.blogspot.com/ us $value = dbmfetch( $dbh, $key ); e fo re du ca tio n on ly 201 Figure 11.1: Reading all records from a DBM database. Determining Whether an Item Exists in a Database Before reading or setting an element in a DBM database, it is sometimes useful to know whether the element exists. You can do this with the dbmexists() function. dbmexists() requires a valid DBM identifier and the name of the element for which you are testing. It returns true if the element exists. print dbmfetch( $dbh, "Tricorder" ); Deleting an Item from a Database requires a valid DBM identifier and the name of the element you want to remove the element did not exist to be deleted. No dbmdelete( $dbh, "Tricorder" ); Adding Complex Data Structures to a DBM Database All data in a DBM database is extracted in string format, so you are limited to storing integers, strings, and doubles. Any other data type will be lost. Let's try to store an array, for example: $array = array( 1, 2, 3, 4 ); $dbh = dbmopen( "./data/test", "c" ) or die("Couldn't open test DBM"); http://i-tronics.blogspot.com/ tf or from the database. It returns true if the item was successfully deleted, and false if co You can delete an item from a database using the dbmdelete() function. dbmdelete() m er cia l, if ( dbmexists( $dbh, "Tricorder" ) ) us e fo re du ca tio n on ly 202 dbminsert( $dbh, "arraytest", $array ); print gettype( dbmfetch( $dbh, "arraytest" ) ); // prints "string" We create an array and store it in the variable $array. We then open a database and attempt to insert an element called "arraytest", passing it the $array variable as the value. We then test the return type from dbmfetch() when attempting to access "arraytest" and ascertain that a string has been returned. In fact, if we printed the value stored in the "arraytest" record, we would get the string "Array". That would seem to wrap up any hopes for storing arrays and objects. data type in string format. The data can then be stored in a database or file until it database. To convert the array in the previous example to a string, we must use the serialize() function. serialize() requires a value of any type and returns a string: $array = array( 1, 2, 3, 4 ); print serialize( $array ); // prints a:4:{i:0;i:1;i:1;i:2;i:2;i:3;i:3;i:4;} returns a value of the appropriate data type. allowed by DBM databases. Listing 11.4 serializes an associative array for each of the items in our list of products and adds the result to our database. 1: <html> 2: <head> 4: </head> 5: <body> 7: <?php Listing 11.4: Adding Complex Data to a DBM Database 3: <title>Listing 11.4 Adding complex data to a DBM database</title> No 10: 11: 12: 13: "Tricorder" tf 6: Adding complex data to database 8: $products = array( "Sonic Screwdriver" => array( price=>"22.50", shipping=>"12.50", color=>"green" ), => array( price=>"55.50", shipping=>"7.50", 9: or co m er cia l, This allows you to store complex data structures within the relatively simple format http://i-tronics.blogspot.com/ us can use the unserialize() function. unserialize() requires a serialized string and e We can now store this string in the DBM database. When we want to resurrect it, we fo re du ca is needed. You can use this technique to store arrays and even objects in a DBM tio n Fortunately, PHP provides a feature that allows you to "freeze-dry" values of any on ly 203 14: 15: 16: 17: 18: 19: 20: 21: 23: 25: 27: ?> 28: </table> 29: </body> 30: </html> ); or die("Couldn't open products DBM"); dbmreplace( $dbh, $key, serialize( $value ) ); "HAL 2000" "ORAC AI" color=>"red" ), => array( price=>"2200.50", shipping=>"34.50", color=>"blue" ), => array( price=>"4500.50", shipping=>"18.50", color=>"pink" ) 22: $dbh = dbmopen( "./data/newproducts", "c" ) 24: while ( list ( $key, $value ) = each ( $products ) ) 26: dbmclose( $dbh ); through the array. For each element, we pass the product name and a serialized Listing 11.5 writes the code that extracts this data. Listing 11.5: Retrieving Serialized Data from a DBM Database 2: <head> 4: 1: <html> 3: <title>Listing 11.5 Retrieving serialized 5: </head> 6: <body> 7: 8: 9: No 10: <p> 11: <table border=1 cellpadding ="5"> 12: <tr> 13: <td align="center"> <b>product</b></td> 14: <td align="center"> <b>color</b> </td> tf or Here at the Impossible Gadget Shop we're offering the following exciting products: co data from a DBM database</title> m er cia l, version of the product array to dbmreplace(). We then close the database. http://i-tronics.blogspot.com/ us arrays of product information as values. We then open the database and loop e We build a multidimensional array, containing the product names as keys and four fo re du ca tio n on ly 204 15: <td align="center"> <b>shipping</b> </td> 16: <td align="center"> <b>price</b> </td> 17: </tr> 18: <?php 19: $dbh = dbmopen( "./data/newproducts", "c" ) 20: or die("Couldn't open test DBM"); 21: $key = dbmfirstkey( $dbh ); 22: while ( $key != "" ) 23: 24: 25: 26: 27: 28: 29: 30: 32: ?> 33: </table> 34: </body> 35: </html> { $prodarray = unserialize( dbmfetch( $dbh, $key ) ); print "<tr><td align=\"left\"> $key </td>"; print "<td align=\"left\">$prodarray[color] </td>\n"; print "<td align=\"right\">\$$prodarray[shipping] </td>\n"; print "<td align=\"right\">\$$prodarray[price] </td></tr>\n"; $key = dbmnextkey( $dbh, $key ); } 31: dbmclose( $dbh ); Listing 11.5 is similar to the example in Listing 11.3. In this case though, we are displaying more fields. We open the database and then use dbmfirstkey() and use unserialize() to reconstruct the product array. It is then simple to print each element of the product array to the browser. Figure 11.2 shows the output from Listing 11.5. dbmnextkey() to loop through each item in the database. We extract the value and No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 205 Figure 11.2: Retrieving serialized data from a DBM database. An Example We now have enough information to build an example using some of the techniques discussed in this hour. Our brief is to build an administration page to enable a site editor to change the prices in the products database created in Listing 11.2. The new ones. The page will not be hosted on a publicly available server, so security is not a problem for this project. First, we must build a form that incorporates all the elements in the database. The user will be able to change any price using a text field and choose which items to delete using a check box. She will also have two text fields for adding a new item to Listing 11.6: Building an HTML Form Based on Content from a DBM Database 1: <? 3: the database. Listing 11.6 shows the code to create the form. administrator should also be able to remove elements from the database and add 2: $dbh = dbmopen( "./data/products", "c" ) 4: ?> No 10: <body> 11: <form action="POST"> tf 5: <html> 6: <head> 7: <title>Listing 11.6 Building an html form based 8: on content from a DBM database</title> 9: </head> or co or die("Couldn't open test DBM"); m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 206 12: <table border="1"> 13: <tr> 14: <td>delete</td> 15: <td>product</td> 16: <td>price</td> 17: </tr> 18: <?php 19: $key = dbmfirstkey( $dbh ); 20: while ( $key != "" ) 21: 22: 23: 24: 25: 26: 27: 28: 29: 31: ?> 32: <tr> 33: <td> </td> { $price = dbmfetch( $dbh, $key ); print "value=\"$key\"></td>"; print "<td>$key</td>"; print "<td> <input type=\"text\" name=\"prices[$key]\" "; print "value=\"$price\"> </td></tr>"; $key = dbmnextkey( $dbh, $key ); } 34: <td><input type="text" name="name_add"></td> 35: <td><input type="text" name="price_add"></td> 37: <tr> 36: </tr> 38: <td colspan=3 align="right"> 39: <input type="submit" value="amend"> 40: </td> 41: </tr> No 43: </form> 45: </html> We start by opening the database as usual. We then begin an HTML form that points 44: </body> back to the current page using PHP's $PHP_SELF variable. Having written some table headers to the screen, we loop through the contents of tf 42: </table> or co m er cia l, http://i-tronics.blogspot.com/ us e 30: dbmclose( $dbh ); fo re du ca print "<tr><td><input type='checkbox' name=\"delete[]\" "; tio n on ly 207 our database using dbmfirstkey() and dbmnextkey() to get each key in turn, and dbmfetch() to extract the value. In the first table cell of each row, we create a check box. Notice that we give all these the name "delete[]". This instructs PHP to construct an array called $delete of all submitted values that share this name. We use the database element name (stored in $key) as the value for each check box. When the form is submitted, therefore, we should have a $delete array with the names of all the database elements that we want to delete. We then print the element name to the browser and create another text field. This field using a similar technique as we did for the previous field. This time, however, name. PHP constructs an associative array called $prices from these submitted fields with the DBM element names as keys. We close the database and revert to HTML mode to write the final fields. These allow the user to add new product and price combinations. Only two fields are required, and we give them the names name_add and price_add. Figure 11.3 shows the output from Listing 11.6. No Now that we have created the form, we need to write code to deal with the user input. This is not as difficult as it sounds. There are three possible actions we can take. First, we can delete items from the database; second, we can amend prices in the database; and third, we can add new elements to the database. If the form has been submitted, we know which items we need to delete because a $delete array variable will have been made available. We need to loop through this array and delete the elements whose names it contains. tf Figure 11.3: Building an HTML form based on content from a DBM database. or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca we include the name of the database element in the square brackets of the field tio n field presents the product price to the user, ready for amendment. We name the on ly 208 if ( isset ( $delete ) ) { while ( list ( $key, $val ) = each ( $delete ) ) { unset( $prices[$val]); dbmdelete( $dbh, $val ); } } page, or if she has not chosen to delete any items, the variable will not exist. If the $delete array, we call dbmdelete() removing the element by that name from the database. We also interfere with another array variable. The $prices array contains all the key value pairs in the database, although some of the values might have been changed by the user. If we do not remove the elements, we delete from the database the $price array as well. The next block of code adds them to the database once again. To update the database according to the user amendments, we have a choice. We choose this option if we expected many users to be using the script at the same time. element in the database: if ( isset ( $prices ) ) { while ( list ( $key, $val ) = each ( $prices ) ) dbmreplace( $dbh, $key, $val ); } We test for the existence of the $prices array. This should contain a new version of the entire database. We loop through the array, calling dbmreplace() for each of its Finally, we need to check whether the user has submitted a new product for inclusion in the database: if ( ! empty( $name_add ) && ! empty( $price_add ) ) dbmreplace( $dbh, "$name_add", "$price_add" ); Instead of testing whether the $name_add and $price_add variables are set, we test whether they are empty. This is a subtle but important difference. When the user submits the form we have built, these variables will always be set. They may, elements. No tf or co m er cia l, As it is, this script will be run by a single administrator, so we opt to update every http://i-tronics.blogspot.com/ us could only update those elements that the user has elected to change. We would e fo re du ca variable exists, we can go ahead and loop through it. For each string held in the tio n First we test that the $delete variable is set. If the user has only just arrived at the on ly 209 however, contain empty strings. We do not want to add empty strings to our database, so we only execute the code to insert new values if neither variable is empty: if ( ! empty( $name_add ) && ! empty( $price_add ) ) dbmreplace( $dbh, "$name_add", "$price_add" ); We use dbminsert() rather than dbmreplace() to guard against the user inadvertently overwriting an element that has already been defined. You can see the complete code in Listing 11.7. Listing 11.7: The Complete Product Maintenance Code 1: <?php 2: $dbh = dbmopen( "./data/products", "c" ) 3: 4: 5: if ( isset ( $delete ) ) 6: 7: 8: 9: 10: 11: 12: 13: 15: 16: 17: 18: 19: 21: 23: } { } { { unset( $prices[$val]); dbmdelete( $dbh, $val ); } or die("Couldn't open test DBM"); while ( list ( $key, $val ) = each ( $delete ) ) 14: if ( isset ( $prices ) ) dbmreplace( $dbh, $key, $val ); 20: if ( ! empty( $name_add ) && ! empty( $price_add ) ) 22: ?> No 24: <html> 25: <head> 26: <title>Listing 11.7 The complete product maintenance code</title> 27: </head> 28: <body> 29: tf or dbminsert( $dbh, "$name_add", "$price_add" ); co m er while ( list ( $key, $val ) = each ( $prices ) ) cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 210 30: <form action="<? print $PHP_SELF; ?>" action="POST"> 31: 32: <table border="1"> 33: <tr> 34: <td>delete</td> 35: <td>product</td> 36: <td>price</td> 37: </tr> 38: 39: <?php 40: $key = dbmfirstkey( $dbh ); 41: while ( $key != "" ) 42: 43: 44: 45: 46: 47: 48: 49: 50: 51: 53: ?> 54: 55: <tr> { $price = dbmfetch( $dbh, $key ); print "value=\"$key\">$/td>"; print "<td>$key</td>"; print "<tr><td><input type='checkbox' name=\"delete[]\" "; print "<td> <input type=\"text\" name=\"prices[$key]\" "; $key = dbmnextkey( $dbh, $key ); } 52: dbmclose( $dbh ); 56: <td> </td> 57: <td><input type="text" name="name_add"></td> 58: <td><input type="text" name="price_add"></td> 59: </tr> 60: 61: <tr> No 62: <td colspan=3 align="right"> 63: <input type="submit" value="amend"> 64: </td> 65: </tr> 66: 67: </table> tf or co m er cia l, http://i-tronics.blogspot.com/ us e print "value=\"$price\"> </td></tr>"; fo re du ca tio n on ly 211 68: </form> 69: 70: </body> 71: </html> In this hour, you learned how to use PHP's powerful DBM functions to store and with dbminsert(), alter it with dbmreplace(), and delete data with dbmdelete(). You learned how to use dbmfetch() to retrieve data. You learned how to use serialize() and unserialize() to save complex data structures to a DBM database. Finally, you worked through an example that uses many of the techniques we have examined. Q&A A A DBM database is a good option when you want to store small amounts of database have the virtue of portability. If you intend to store large amounts of data or many fields, consider using a SQL database, such as MySQL. Workshop The Workshop provides quiz questions to help you solidify your understanding of the hour's lesson. Quiz answers are provided in Appendix A. Quiz No tf What function would you use to open a DBM database? What function would you use to insert a record into a DBM database? What function would you use to replace a record in a DBM database? How would you access a record from a DBM database by name? or material covered. Try to understand the quiz answers before continuing to the next co m er cia l, relatively simple data (typically name/value pairs). Scripts built to use a DBM http://i-tronics.blogspot.com/ us e Q When should I use a DBM database as opposed to a SQL database? fo re du ca tio you can use with other DBM functions. You learned how to add data to a database n retrieve data. You learned how to use dbmopen() to acquire a DBM identifier, which on ly Summary 212 How would you get the name (as opposed to the value) of the first element in a DBM database? How would you get subsequent element names? How would you delete a named element from a DBM database? Activities Create a DBM database to keep track of user names and passwords. Create a script that allows users to register their combinations. Don't forget to check for Create an authentication script that checks a user name and password. If the message. Otherwise, represent the login form to the user. No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca user input matches an entry in the database, present the user with a special tio n duplications. on ly 213 Hour 12: Database Integration— MySQL One of the defining features of PHP is the ease with which you can connect to and manipulate databases. In this hour, we will concentrate on MySQL, but you will find well with the spirit of PHP in that it is free to the individual user, yet remains a Furthermore, versions of MySQL are available for multiple platforms. You can download MySQL from http://www.mysql.org. In this hour, you will learn A few SQL samples How to select a database About error handling How to add data to a table How to retrieve data from a table How to alter data in a table About the structure of databases How to connect to the MySQL database server NEW TERM m er A (Very) Brief Introduction to SQL SQL stands for Structured Query Language. It provides a standardized syntax by which different types of database can be queried. Most SQL database products provide their own extensions to the language, just as many browsers provide their own extensions to This book cannot even begin to describe the intricacies of SQL. Nonetheless, we can No fill in some background about MySQL and SQL in general. MySQL runs as a server daemon to which users on the same or even remote machines can connect. Once connected to the server, you can select a database if you have the privileges to do so. Within a database, there will be a varying number of tables of data. Each table is arranged in rows and columns. The intersection between a row and a column is the point at which each item of data you want to store and access sits. Each column only tf or co HTML. Nonetheless, an understanding of SQL enables you to work with a wide range of database products across multiple platforms. cia l, http://i-tronics.blogspot.com/ us e fo re du ca powerful tool that can be used as the basis of demanding real-world projects. tio similar functions for many of the databases that PHP supports. Why MySQL? It fits n on ly Overview 214 accepts a predefined type of data, INT for integer, for example, or VARCHAR for a variable number of characters up to a defined limit. To create a new table within a database we have selected, we might use a SQL query like the following: CREATE TABLE mytable ( first_name VARCHAR(30), second_name VARCHAR(30), age INT); Our new table has three columns. first_name and second_name can contain strings of up to 30 characters. age can contain any integer. To add data to this table, we could use an INSERT statement: 36 ); The field names to which we want to add data are defined in the first set of parentheses. The values we want to insert are defined in the second. To acquire all the data in a table, we would use a SELECT statement: SELECT * * FROM mytable; The " " symbol represents a wildcard which means "all fields." To acquire the information from a single field, you can use the column name in place of the SELECT age FROM mytable; wildcard: To change the values already stored in a table, you can use an UPDATE statement: This changes the first_name field in every row to "Bert". We can narrow the focus of SELECT and UPDATE statements with a WHERE clause. For example, returns only those rows whose first_name fields contain the string "Bert". This next example UPDATE mytable SET first_name = "Bert" WHERE second_name = "Baker"; changes the first_name fields of all rows whose second_name fields contain "Baker". For more information on SQL, see Sams Teach Yourself SQL in 21 Days by Ryan K. SELECT * No Stephens et. al. Connecting to the Database Server Before you can begin working with your database, you must first connect to the server. PHP provides the mysql_connect() function to do just this. mysql_connect() does not require any arguments but accepts up to three strings: the hostname, a tf or co m er FROM mytable WHERE first_name = 'Bert'; cia l, UPDATE mytable SET first_name = 'Bert'; http://i-tronics.blogspot.com/ us e fo re du ca tio n INSERT INTO mytable ( first_name, second_name, age ) VALUES ( 'John', 'Smith', on ly 215 usename, and a password. If you omit any or all of these arguments, the function assumes localhost as the host and that no password or username has been set up in the mysqluser table, unless defaults have been set up in the php.ini file. Naturally, this is unwise for anything but a test database, so we will always include a username and password in our examples. mysql_connect() returns a link identifier if the connection is successful. You can store this return value in a variable so that you can continue to work with the database server. The following code fragment uses mysql_connect() to connect to the MySQL die( "Couldn't connect to MySQL" ); If you are using PHP in conjunction with Apache, you could also connect to the database server with mysql_pconnect(). From the coder's perspective, this function works in exactly the same way as mysql_connect(). In fact, there is an important difference. If you use this function, the connection does not die when your script the MySQL server). Instead, the connection is left active, waiting for another process to call mysql_pconnect(). In other words, the overhead of opening a new call to the script has left the connection open. connection to the server can be saved if you use mysql_pconnect() and a previous stops executing or if you call mysql_close() (which ends a standard connection to Selecting a Database which database we want to work with. You can select a database with the optionally accepts a link identifier. If you omit this, the identifier returned from the last connection to the server will be assumed. mysql_select_db() returns true if the No database exists and you are able to access it. In the following fragment, we select a database called sample. $database = "sample"; mysql_select_db( $sample ) or die ( "Couldn't open $sample ); Finding Out About Errors tf or mysql_select_db() function. mysql_select_db() requires a database name and co Now that we have established a connection to the MySQL daemon, we must choose m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca if ( ! $link ) tio $link = mysql_connect( "localhost", "root", "n1ckel" ); n database server: on ly 216 So far we have tested the return values of the MySQL functions that we have used and called die() to end script execution if a problem occurs. You might, however, want to print more informative error messages to the browser to aid debugging. MySQL sets an error number and an error string whenever an operation fails. You can access the error number with mysql_errno(), and the error string with mysql_error(). Listing 12.1 brings our previous examples together into a simple script that connects to the server and selects a database. We use mysql_error() to make our error messages more useful. Listing 12.1: Opening a Connection and Selecting a Database 1: <html> 2: <head> 3: <title>Listing 12.1 Opening a connection and 4: selecting a database</title> 5: </head> 6: <body> 7: <?php 8: $user = "harry"; 9: $pass = "elbomonkey"; 10: $db = "sample"; 11: $link = 13: 12: if ( ! $link ) 14: print "Successfully connected to server<P>"; 15: mysql_select_db( $db ) 16: or die ( "Couldn't open $db: ".mysql_error() ); 17: print "Successfully selected database \"$db\"<P>"; 18: mysql_close( $link ); 19: ?> 20: </body> 21: </html> No If we change the value of the $db variable to "notthere", we will be attempting to open a nonexistent database. The output of our die() function call will look something like the following: Couldn't open sample2: Access denied for user: 'harry@localhost' to database 'sample2' Adding Data to a Table tf or co m er cia l, die( "Couldn't connect to MySQL" ); http://i-tronics.blogspot.com/ us mysql_connect( "localhost", $user, $pass ); e fo re du ca tio n on ly 217 Now that we have access to our database, we can add information to one of its tables. For the following examples, imagine that we are building a site that allows people to buy domain names. We have created a table within the sample database called domains. The table was created with five columns: a primary key field called id that will automatically increment an integer as data is added, a domain field that will contain a variable number of characters (VARCHAR), a sex field that will contain a single character, was used in the MySQL client to create the table: create table domains ( id INT NOT NULL AUTO_INCREMENT, PRIMARY KEY( id ), domain VARCHAR( 20 ), sex CHAR(1), mail VARCHAR( 20 ) ); and a mail field that will contain a user's email address. The following SQL statement To add data to this table, we will need to construct and execute a SQL query. PHP provides the mysql_query() function for this purpose. mysql_query() requires a string containing a SQL query and, optionally, a link identifier. If the identifier is omitted, the query is sent to the database server to which you last connected. contains a syntax error, or if you don't have permission to access the database in question, then query() returns false. Note that a successful query does not and uses mysql_query() to send an INSERT statement to the domains table in the sample database. 1: <html> 2: <head> 4: </head> 5: <body> 6: <?php Listing 12.2: Adding a Row to a Table necessarily result in any altered rows. Listing 12.2 extends our previous examples Mysql_query() returns a positive value if the query is successful. If your query 3: <title>Listing 12.2 Adding a row to a table</title> No 10: $link = 12: tf 7: $user = "harry"; 8: $pass = "elbomonkey"; 9: $db = "sample"; mysql_connect( "localhost", $user, $pass ); 11: if ( ! $link ) die( "Couldn't connect to MySQL" ); 13: mysql_select_db( $db, $link ) or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 218 14: 16: or die ( "Couldn't open $db: ".mysql_error() ); values( '123xyz.com', 'F', 'sharp@adomain.com' )"; 15: $query = "INSERT INTO domains ( domain, sex, mail ) 17: mysql_query( $query, $link ) 18: or die ( "Couldn't add data to \"domains\" table: " 19: .mysql_error() ); 20: mysql_close( $link ); 21: ?> 22: </body> 23: </html> Of course, every time we reload the script in Listing 12.2, the same data is added to a new row. Listing 12.3 creates a script that will enter user input into our database. Listing 12.3: Adding User Input to a Database 1: <html> 2: <head> 4: </head> 5: <body> 6: <?php 8: 9: 10: 11: 12: 13: 14: 15: 16: 18: 19: 20: 21: function add_to_database( $domain, $sex, $mail, &$dberror ) 22: 23: { $user = "harry"; { 3: <title>Listing 12.3 Adding user input to a database</title> // check user input here! $ret = add_to_database( $domain, $sex, $mail, $dberror ); if ( ! $ret ) else } No 17: else tf or write_form(); } co print "Error: $dberror<BR>"; print "Thank you very much"; { m er $dberror = ""; cia l, 7: if ( isset( $domain ) && isset( $sex ) && isset( $domain ) ) http://i-tronics.blogspot.com/ us e fo re du ca Notice that we did not insert a value for the id column. This field will auto-increment. tio n on ly 219 24: 25: 26: 27: 28: 29: 30: 31: 32: 33: 34: 35: 36: 38: 39: 40: 41: 42: 43: 44: 45: 46: 48: 49: 50: 51: 52: 53: 54: 55: 56: { } $pass = "elbomonkey"; $db = "sample"; $link = { $dberror = "Couldn't connect to MySQL server"; return false; } if ( ! mysql_select_db( $db, $link ) ) { $dberror = mysql_error(); return false; } mysql_pconnect( "localhost", $user, $pass ); if ( ! $link ) 37: $query = "INSERT INTO domains ( domain, sex, mail ) values( '$domain', '$sex', '$mail' )"; if ( ! mysql_query( $query, $link ) ) { $dberror = mysql_error(); return false; } return true; 47: function write_form() global $PHP_SELF; print "<form action=\"$PHP_SELF\" method=\"POST\">\n"; print "<input type=\"text\" name=\"domain\"> "; print "The domain you would like<p>\n"; No 57: 58: 59: 60: 61: ?> tf or print "<input TYPE=\"text\" name=\"mail\"> "; print "Your mail address<p>\n"; print "<select name=\"sex\">\n"; print "\t<option value=\"F\"> Female\n"; print "\t<option value=\"M\"> Male\n"; print "</select>\n"; print "<input type=\"submit\" value=\"submit!\">\n</form>\n"; } co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 220 62: </body> 63: </html> To keep the example brief, we have left out one important process in Listing 12.3. We are trusting our users. We should in fact check any kind of user input. We deal with the string functions that help you test user input in Hour 17, "Working with Strings." We check for the variables $domain, $sex, and $mail. If they exist, we can be fairly certain that the user has submitted data, and we call the add_to_database() The add_to_database() function requires four arguments: the $domain, $sex, and populate this last argument with any error strings we encounter. For this reason, we accept $dberror as a reference to a variable. Any changes made to this string within the function will change the original argument rather than a copy. We attempt to open a connection to the MySQL server. If this fails, we assign an error string to $dberror and end the execution of the function by returning false. We select the database that contains the domains table and build a SQL query to insert for us. If either mysql_select_db() or mysql_query() fail, we assign the value returned by mysql_error() to $dberror and return false. Assuming that all went well, Back in the calling code, we can test the return value from add_to_database(). If the function returns true, we can be sure that we have added to the database and the $dberror variable that we passed to add_to_database() will now contain useful information, so we include it in our error message. If our initial if statement fails to find $domain, $sex, or $mail variables, we can assume that no data has been submitted and call another user-defined function, write_form(), which outputs an HTML form to the browser. thank the user. Otherwise, we write an error message to the browser. We know that the function returns true. the user-submitted values. We pass this to mysql_query(), which makes the query No Acquiring the Value of an Automatically Incremented Field In our previous examples, we have added data to our database without worrying about the id column, which automatically increments as data is inserted. If we need the value of this field for a record at a later date, we can always extract it with a SQL query. What if we need the value straight away, though? It would be wasteful to tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca $mail variables submitted by the user, and a string variable called $dberror. We tio n function. on ly 221 look it up. Luckily, PHP provides mysql_insert_id(), a function that returns the value of an auto-incremented key field after a SQL INSERT statement has been performed. mysql_insert_id() optionally accepts a link identifier as an argument. With no arguments, it works with the most recent link established. So, if we want to tell a user the number we have allocated to her order, we could call $query = "INSERT INTO domains ( domain, sex, mail ) values( '$domain', '$sex', '$mail' )"; mysql_query( $query, $link ); $id = mysql_insert_id(); print "Thank you. Your transaction number is $id. Please quote it in any queries."; Accessing Information mysql_query() to make a SELECT query. How do you use this to look at the returned returns a result identifier. You can pass this identifier to other functions to access and gain information about a resultset. Finding the Number of Rows Found by a Query You can find the number of rows returned as a result of a SELECT query using the returns a count of the rows in the set. Listing 12.4 uses a SQL SELECT statement to request all rows in the domains table and then uses mysql_num_rows() to determine the table's size. Listing 12.4: Finding the Number of Rows Returned by a SELECT Statement with mysql_num_rows() 1: <html> 2: <head> 3: <title>Listing 12.4 Using mysql_num_rows()</title> No tf or mysql_num_rows() function. mysql_num_rows() requires a result identifier and co m er cia l, rows, though? When you perform a successful SELECT query, mysql_query() http://i-tronics.blogspot.com/ us retrieving the information that it contains. As you might guess, you can use e Now that we can add information to a database, we need to look at strategies for fo re du ca tio n on ly mysql_insert_id() directly after adding the user's data to our database. 222 4: </head> 5: <body> 6: <?php 7: $user = "harry"; 8: $pass = "elbomonkey"; 9: $db = "sample"; 10: $link = mysql_connect( "localhost", $user, $pass ); 12: die( "Couldn't connect to MySQL" ); 14: or die ( "Couldn't open $db: ".mysql_error() ); * 15: $result = mysql_query( "SELECT FROM domains" ); 16: $num_rows = mysql_num_rows( $result ); 17: print "There are currently $num_rows rows in the table<P>"; 18: mysql_close( $link ); 19: ?> 20: </body> 21: </html> The mysql_query() function returns a result identifier. We then pass this to mysql_num_rows(), which returns the total number of rows found. Accessing a Resultset a loop to access each found row in turn. PHP maintains an internal pointer that No keeps a record of your position within a found set. This moves on to the next row as each one is accessed. You can easily get an array of the fields in each found row with mysql_fetch_row(). This function requires a result identifier, returning an array containing each field in the row. When the end of the found set is reached, mysql_fetch_row() returns false. Listing 12.5 outputs the entire domains table to the browser. tf After you have performed a SELECT query and gained a result identifier, you can use or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca 13: mysql_select_db( $db, $link ) tio n 11: if ( ! $link ) on ly 223 Listing 12.5: Listing All Rows and Fields in a Table 1: <html> 2: <head> 3: <title>Listing 12.5 Listing all rows and fields in a table</title> 4: </head> 5: <body> 6: <?php 7: $user = "harry"; 8: $pass = "elbomonkey"; 9: $db = "sample"; 10: $link = mysql_connect( "localhost", $user, $pass ); 11: if ( ! $link ) 12: die( "Couldn't connect to MySQL" ); 13: mysql_select_db( $db, $link ) 14: or die ( "Couldn't open $db: ".mysql_error() ); 16: $num_rows = mysql_num_rows( $result ); 17: print "There are currently $num_rows rows in the table<P>"; 18: print "<table border=1>\n"; 20: 21: 22: 23: 24: 25: { foreach ( $a_row as $field ) No 26: print "</table>\n"; 27: mysql_close( $link ); 28: ?> 29: </body> tf or print "</tr>\n"; } co print "<tr>\n"; print "\t<td>$field</td>\n"; m er 19: while ( $a_row = mysql_fetch_row( $result ) ) cia l, http://i-tronics.blogspot.com/ us 15: $result = mysql_query( "SELECT e * FROM domains" ); fo re du ca tio n on ly 224 30: </html> After we have connected to the server and selected the database, we use mysql_query() to send a SELECT statement to the database server. We store the returned result pointer in a variable called $result. We use this to acquire the number of found rows as before. In the test expression of our while statement, we assign the result of mysql_fetch_row() to the variable $a_row. Remember that an assignment operator returns the value of its right-hand operand, so the assignment resolves to true as long as mysql_fetch_row() returns a positive value. Within the body of the while element to the browser embedded in a table cell. statement, we loop through the row array contained in $a_row, outputting each You can also access fields by name in one of two ways. mysql_fetch_array() returns a numeric array, as does mysql_fetch_row() It also returns an associative array, with the names of the fields as the keys. The following fragment rewrites the while statement from Listing 12.5, incorporating mysql_fetch_array(): while ( $a_row = mysql_fetch_array( $result ) ) { print "<TR>\n"; print "<TD>$a_row[mail]</TD><TD>$a_row[domain]</TD>\n"; print "</TR>\n"; } print "</TABLE>\n"; following fragment once again rewrites the while statement from Listing 12.5, this No time incorporating mysql_fetch_object(): print "<table border=1>\n"; while ( $a_row = mysql_fetch_object( $result ) ) { print "<tr>\n"; print "<td>$a_row->mail<td><td>$a_row->domain</td>\n"; http://i-tronics.blogspot.com/ tf mysql_fetch_object(). The field names become the names of the properties. The or You can also extract the fields from a row as properties of an object with co m er cia l, us e print "<TABLE BORDER=1>\n"; fo re du ca tio n on ly 225 print "</tr>\n"; } print "</table>\n"; Both mysql_fetch_array() and mysql_fetch_object() make it easier for you to longer than mysql_fetch_row() to execute. Changing Data You can change data using the mysql_query() function in conjunction with an UPDATE statement. Once again, a successful UPDATE statement does not mysql_affected_rows() to discover whether you have changed data in your table. mysql_affected_rows() optionally accepts a link identifier. If this is missing, the most recent connection is assumed. This function can be used with any SQL query that can alter data in a table row. Listing 12.6 builds a script that allows an administrator to change any of the values in the domain column of our example table. 1: <html> 2: <head> Listing 12.6: Using mysql_query() to Alter Rows in a Database necessarily change any rows. You need to use tio a 4: to alter rows in a database</title> 5: </head> 6: <body> 7: <?php 9: $pass = "elbomonkey"; 10: $db = "sample"; 11: $link = 13: 12: if ( ! $link ) No 14: mysql_select_db( $db, $link ) or die ( "Couldn't open $db: ".mysql_error() ); { $query = "UPDATE domains SET domain = '$domain' where id=$id"s; $result = mysql_query( $query ); 15: 16: if ( isset( $domain ) && isset( $id ) ) 17: 18: 19: tf or die( "Couldn't connect to MySQL" ); co 8: $user = "harry"; mysql_connect( "localhost", $user, $pass ); m er cia l, 3: <title>Listing 12.6 Using mysql_query() http://i-tronics.blogspot.com/ us e fo re du ca function n on ly to call selectively extract information from a row. Neither of these functions takes much 226 20: 21: 23: 24: 25: ?> 26: <form action="<? print $PHP_SELF ?>" method="POST"> 27: <select name="id"> 28: <? 29: $result = mysql_query( "SELECT domain, id FROM domains" ); 30: while( $a_row = mysql_fetch_object( $result ) ) 31: 32: 33: 34: 35: 36: 38: ?> 39: </select> 41: </form> 42: </body> 43: </html> } { print "<OPTION VALUE=\"$a_row->id\""; if ( isset($id) && $id == $a_row->id ) print " SELECTED"; print "> $a_row->domain\n"; if ( ! $result ) die ("Couldn't update: ".mysql_error()); " row(s) changed</h1><p>"; } 22: print "<h1>Table updated ". mysql_affected_rows() . 37: mysql_close( $link ); 40: <input type="text" name="domain"> We open a connection to the database server and select a database as normal. We then test for the presence of the variables $domain and $id. If these are present, we build a SQL UPDATE query that changes the value of the domain field where the id field contains the same value as our $id variable. We do not get an error if a nonexistent id is used or if the $domain variable is the same as the current value for We print this return value (usually 1 in this example) to the browser. We print an HTML form to allow the administrator to make her changes. Note that we use mysql_query() once again to extract the values of the id and domain column and incorporate them in an HTML SELECT element. The administrator will use this pop-up menu to choose which domain to change. If the administrator has already submitted the form and the id value she chose matches the value of the id field we are currently outputting, we add the string SELECTED to the OPTION element. This domain in the relevant row. Instead, the mysql_affected_rows() simply returns 0. No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 227 ensures that her changed value will be instantly visible to her in the menu. Getting Information About Databases Until now, we have primarily looked at adding information to and extracting find out about the number and structure of databases available from the current connection. Listing Databases You can get a list of all databases available from the current connection with the function mysql_list_dbs(). This function optionally accepts a link identifier and returns a result identifier that can be used to output all the databases available. To do this, you can call the function mysql_tablename() for each of the databases found. mysql_tablename() accepts two arguments: a result pointer and the index of a database. It returns the name of the database referenced. Databases are indexed mysql_list_dbs() by calling mysql_num_rows() with the result identifier returned by mysql_list_dbs(). from 0. You can find the total number of databases found by your call to Listing 12.7 connects to the MySQL daemon and prints a list of databases to the browser. Listing 12.7: Listing the Databases Available in a Connection 1: <html> 2: <head> 3: <title>Listing 12.7 Listing the databases No 10: $link = tf 5: </head> 6: <body> 7: <?php 8: $user = "harry"; 9: $pass = "elbomonkey"; mysql_connect( "localhost", $user, $pass ); 11: if ( ! $link ) or 4: available in a connection</title> co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly information from a database. PHP provides a range of functions that allow you to 228 12: die( "Couldn't connect to MySQL" ); 13: $db_res = mysql_list_dbs( $link ); 14: $num = mysql_num_rows( $db_res ); 15: for( $x = 0; $x < $num; $x++ ) 16: print mysql_tablename( $db_res, $x )."<br>"; 17: mysql_close( $link ); 18: ?> 19: </body> 20: </html> Our call to mysql_list_dbs() gives us a result pointer. We can use the result pointer to get the total number of items found by passing it to mysql_num_rows() as an argument. We assign this total to a variable ($num), which we then use in a for statement. For each iteration, we pass mysql_tablename() our result pointer and an index databases found. Figure 12.1 shows the output from Listing 12.7. No Figure 12.1: Listing available databases. You could also use the result identifier returned by mysql_list_dbs() in the same way as that returned by mysql_query() for a SELECT query. In other words, you can pass the identifier to mysql_fetchrow(). mysql_fetchrow() returns an array with the database name in the first element of the array. tf or co m er cia l, http://i-tronics.blogspot.com/ us e number, $x, which is incremented from 0 to one less than the total number of fo re du ca tio n on ly 229 Listing the Tables Within a Database Given a database name and (optionally) a link identifier, you can list all the tables in a database using the mysql_list_tables() function. If the database can be found and can use with fetch functions such as mysql_fetch_row(). Alternatively, you can use the mysql_tablename() function as we did with mysql_list_dbs(). you have the right privileges, mysql_list_tables() returns a result identifier that you The following fragment uses mysql_list_tables() to list all the tables in a database: $result = mysql_list_tables( "sample", $link ); while ( $tab_rows = mysql_fetch_row( $result ) ) print "$tab_rows[0]<BR>\n"; Listing and Exploring Fields When you acquire a result identifier from mysql_query() using a SELECT query, you can calculate the number of columns returned using mysql_num_fields(). mysql_num_fields() requires a result identifier and returns an integer representing the number of fields found: $result = mysql_query( "SELECT $num_fields = mysql_num_fields( $result ); Each field in a found set has an index (beginning at zero). Using a result identifier and a field's index number, you can discover many of the field's attributes, including mysql_field_name(): tf or To get the name of a field, pass a result identifier and an index number to co its name, type, maximum length, and flags. m er $result = mysql_query( "SELECT No $num_fields = mysql_num_fields( $result ); for ( $x=0; $x<$num_fields; $x++ ) mysql_field_name( $result, $x ) . "<BR>\n"; To get the maximum length of a mysql_field_len(): cia l, us * from domains" ); * from domains" ); e http://i-tronics.blogspot.com/ fo re du ca field, pass the same arguments to tio n on ly 230 $result = mysql_query( "SELECT * from domains" ); $num_fields = mysql_num_fields( $result ); for ( $x=0; $x<$num_fields; $x++ ) mysql_field_len( $result, $x ) . "<BR>\n"; to mysql_field_flags(): $result = mysql_query( "SELECT * from domains" ); for ( $x=0; $x<$num_fields; $x++ ) mysql_field_flags( $result, $x ) . "<BR>\n"; You can also get the type of a field with the mysql_field_type() function. It requires the same arguments: $result = mysql_query( "SELECT * from domains" ); $num_fields = mysql_num_fields( $result ); mysql_field_flags( $result, $x ) . "<BR>\n"; Database Structure— Bringing It All Together Listing 12.8 combines all these techniques to list every database, table, and field available to us from a connection. Listing 12.8: Listing Every Database, Table, and Field 2: <head> 1: <html> 4: </head> No 10: $link = 12: tf 5: <body> 6: <?php 7: $user = "root"; 8: $pass = "n1ckel"; mysql_connect( "localhost", $user, $pass ); 9: $db = "sample"; 11: if ( ! $link ) die( "Couldn't connect to MySQL" ); or 3: <title>Listing 12.8 Listing every database, table, and field</title> co m er cia l, http://i-tronics.blogspot.com/ us for ( $x=0; $x<$num_fields; $x++ ) e fo re du ca tio n $num_fields = mysql_num_fields( $result ); on ly To get the flags associated with a field, pass a result identifier and an index number 231 13: $db_res = mysql_list_dbs( $link ); 14: while ( $db_rows = mysql_fetch_row( $db_res ) ) 15: 16: 17: 18: 19: 20: 21: 22: 23: 24: 25: 26: 27: 28: 29: 30: 31: 32: 33: 34: 35: 36: 37: 38: 39: 40: 41: 42: 43: 44: 45: { print "<b>$db_rows[0]</b>\n"; if ( !@mysql_select_db( $db_rows[0], $link ) ) { print "<dl><dd>couldn't connect -- " . mysql_error() ." </dl>"; continue; } $tab_res = mysql_list_tables( $db_rows[0], $link ); print "\t<dl><dd>\n"; while ( $tab_rows = mysql_fetch_row( $tab_res ) ) { print "\t<b>$tab_rows[0]</b>\n"; $query_res = mysql_query( "SELECT print "\t\t<dl><dd>\n"; { print "\t\t<i>"; $num_fields = mysql_num_fields( $query_res ); for ( $x=0; $x<$num_fields; $x++ ) print mysql_field_type( $query_res, $x ); print mysql_field_len( $query_res, $x ); print "</i> <b>"; print mysql_field_name( $query_res, $x ); print "</b> <i>"; print mysql_field_flags( $query_res, $x ); print "</i><br>\n"; No 46: mysql_close( $link ); 47: ?> 48: </body> 49: </html> tf or print "\t</d1>\n"; } co print "\t\t</d1>\n"; } m er } cia l, print "</i> <i>"; http://i-tronics.blogspot.com/ us e fo re du ca * from $tab_rows[0]" ); tio n on ly 232 We connect to the MySQL server in the usual way and call mysql_list_dbs() to acquire a result identifier. We pass this to mysql_fetch_row(), which returns the name of every database available in turn (stored in the first element of the $db_rows array). We pass each database name to mysql_select_db(). If we don't have permission to access the database, we print a message to the browser and use the continue statement to begin the next iteration. If we are able to select the database, we can go ahead and print its table names. We pass the database name to mysql_list_tables() and acquire a new result to list each table name. We print the table name and then use it to construct a SQL mysql_query() and acquire yet another result identifier. to get the number of fields in the found set. The result identifier acquired from mysql_query() is passed to mysql_num_fields() We use a for statement to loop from zero to one less than the total number of columns in the resultset. The counter variable ($x) represents the index number of each field in the table that we want to test. We call each of the field test functions we When this script is run, we should get a reasonably neat listing of every database, table, and field available from a connection. Figure 12.2 shows part of the output from this script. covered in the last section in turn, outputting their return values to the browser. No Figure 12.2: Listing every database, table, and field. Summary tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca SELECT query, requesting all fields and rows from the table. We pass the query to tio n identifier. Once again, we can pass this to mysql_fetch_row(), beginning a new loop on ly 233 In this hour, we covered some of the basics of storing and retrieving information from a MySQL database. You should now be able to establish a connection to the MySQL server using mysql_connect() or mysql_pconnect(). You should be able to select a database with mysql_select_db(). If the selection fails, you should be able to discover more about the error with mysql_error(). You should be able to make SQL queries using mysql_query(). With the result number of rows you have transformed. tables, and fields accessible to you and to find out more about the attributes of individual fields. Q&A A There are functions for mSQL that mirror those for MySQL almost exactly. Other database servers have corresponding PHP functions that support their features and capabilities. The common feature of many suites of database function is the have little problem adapting scripts across database servers. Q What is the best way of writing code that can be easily adapted to work with different database servers? capability to send SQL queries. If you work with ANSI (standard) SQL, you should only need to change a discrete portion of your code without disturbing the project as No a whole. Workshop tf library. If you need to rewrite your project to work with a different database, you will or A It is often a good idea to group code that queries a database into a single class or co m er cia l, http://i-tronics.blogspot.com/ us other SQL databases? e Q This hour is specific to MySQL. How transferable are these examples to fo re du ca You should be able to use PHP's MySQL functions to list the number of databases, tio n identifier this function returns, you should be able to access data, or discover the on ly 234 The Workshop provides quiz questions to help you solidify your understanding of the material covered. Try to understand the quiz answers before continuing to the next hour's lesson. Quiz answers are provided in Appendix A. Quiz How would you open a connection to a MySQL database server? What function would you use to select a database? What function would you use to send a SQL query to a database? What does the mysql_insert_id() function do? functions that you might use to access each row returned. Assuming that you have sent a successful SELECT query to MySQL, name three Assuming that you have sent a successful UPDATE query to MySQL, what function might you use to determine how many rows have been updated? What function would you call if you want to list all databases available from a MySQL server? What function would you use to list all tables within a database? Activities Create a database with three fields: email (up to 70 characters), message (up to a script to allow users to populate the database. Create a script that displays the information from the database you created in activity 1. No tf or co m er cia l, 250 characters), and date (an integer that will contain a UNIX time stamp). Build http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 235 Hour 13: Beyond the Box Overview In this hour, we will look at some of the functions that allow you to gain information from or interact with the outside world. In this hour, you will learn More about environmental variables The anatomy of an HTTP connection How to acquire a document from a remote server How to create your own HTTP connection How to send email from your scripts How to connect to other network services Environmental Variables You have already encountered some of the environmental variables that PHP, in conjunction with your server, makes available for you. Some of these variables are though, that these variables might not be available on your system or with your server software, so it is a good idea to check before using them in scripts. Table 13.1 visitors. useful in discovering more information about your visitors. You should be aware, Table 13.1: Some Useful Environmental Variables Variable $HTTP_REFERER $HTTP_USER_AGENT co or No $REMOTE_HOST $QUERY_STRING tf $REMOTE_ADDR m er cia l, lists some of the variables that you might be able to use to find out more about your Description The URL from which the current script was called (the misspelling is deliberate). Information about the browser and platform that the visitor is using. The visitor's IP address. The visitor's hostname. The (encoded) string that may be appended to the URL (in format the ?akey=avalue&anotherkey=anothervalue). These keys and values should become available to your scripts in global variables. $PATH_INFO Additional information that may be appended to the http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 236 URL. Listing 13.1 builds a script that outputs the contents of these variables to the browser. Listing 13.1: Listing Some Environmental Variables 1: <html> 3: <title>Listing 13.1 Listing some environmental variables</title> 4: </head> 5: <body> 6: <?php "REMOTE_ 8: foreach ( $envs as $env ) 9: 10: 11: 12: 13: ?> 14: </body> 15: </html> } { if ( isset( $$env ) ) 2: <head> 7: $envs = array( "HTTP_REFERER", "HTTP_USER_AGENT", "REMOTE_ADDR", HOST", "QUERY_STRING", "PATH_INFO" ); print "$env: ${$env}<br>"; Notice our use of dynamic variables to convert strings into variables of the same name. We covered this technique in Hour 4, "The Building Blocks." Figure 13.1 shows the output from Listing 13.1. The data in Figure 13.1 was generated as a result of calling the script from a link in another page. The link that <A HREF='eg13.1.php/my_path_info?query_key=query_value'>go</A> called the script looked like this: As you can see, the link uses a relative path to call listing13.1.php. No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 237 Figure 13.1: Printing some environmental variables to the browser. Additional path information (my_path_info) is included after the document name, which becomes available in $PATH_INFO. We have hard-coded a query string (query_key=query_value) into the link, which becomes available in $QUERY_STRING. You will most often encounter a query string when using a form with a GET method argument, but you can also build your own name value pairs separated by ampersand (&) symbols. These pairs are URL encoded, which means that any characters that are illegal or have other meanings access to the entire query string in the $QUERY_STRING environmental variable, you will rarely need to use this fact. Each key name will be available to you as a decoded value ("query_value"). The $HTTP_REFERER variable can be useful to you if you want to track which hits on your script originate from which links. Beware, though; this and other environmental variables can be easily faked. You will see how later in this hour. Because correcting it would cause compatibility problems, we are stuck with the avoid relying upon it. You can parse the $HTTP_USER_AGENT variable to work out the platform and browser that the visitor is using. Once again, this can be faked. This variable can be useful if you need to present different HTML code or JavaScript according to the browser type and version the visitor is using. Hour 17, "Working with Strings," and Hour 18, "Working with Regular Expressions," will give you the tools you need to extract any information you want from this string. incorrect spelling of 'referrer'. Not all browser will supply this header, so you should global variable ($query_value in our example) that will hold a corresponding in URLs will be converted to their hexadecimal equivalents. Although you have query strings to pass information from page to page. The query string consists of No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 238 The $REMOTE_ADDR variable contains the user's IP address and can be used to track unique visitors to your site. Be aware, though, that many Web users do not have a fixed IP address. Instead, their Internet service providers dynamically allocate them an address when they dial up. This means that a single IP address might be used by different visitors to your site, and that a single visitor might enter using different IP addresses from the same account. The $REMOTE_HOST variable might not be available to you, depending on the configuration of your server. If available, it will hold the hostname of the user. The presence of this variable requires that the server look up the hostname for every this variable, you can acquire it yourself using the value of the $REMOTE_ADDR A Brief Summary of an HTTP Client/Server Negotiation It is beyond the scope of this book to explore all the information exchanged between server and client when a request is made, not least because PHP handles most of these details for you. It is a good idea to gain a basic understanding of this process, however, especially if you intend to write scripts that fetch Web pages or check the status of Web addresses. NEW TERM HTTP stands for hypertext transfer protocol. It is essentially a set of rules that define the process by which a client sends a request and a server returns a response. Both client and server provide information about themselves and the data to be transferred. Much of this information becomes available to you in environmental variables. The Request No consists of up to three components: A request line A header section An entity body The request line is mandatory. It consists of a request method, typically GET, HEAD, or POST; the address of the document to required; and the HTTP version to be used tf A client requests data from the server according to a strict set of rules. The request or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca variable. You will see how to do this later in the hour. tio n request, so it is often disabled for the sake of efficiency. If you don't have access to on ly 239 (HTTP/1.0 or HTTP/1.1). A typical request for a document called mydoc.html might look like this: GET /mydoc.html HTTP/1.0 The client is making a GET request. In other words, it is requesting an entire document but sending no data itself (in fact you can send small amounts of data as part of a GET request by adding a query string to the URL. The HEAD method would be used if you only wanted information about a document. The POST method is used to transfer data from a client to the server, usually from an HTML form. that a request is complete, an empty line must be sent. Most clients will follow the request line with a header section in which name/value pairs can be sent to the server. Some of these will become available to you as environmental variables. Each client header consists of a key and value on one line separated by a colon. Table 13.2 lists a few of these. Table 13.2: Some Client Headers Name Accept e fo re du ca tio The with. The data The sets The The The request line is enough in itself to make a valid GET request. To inform the server us types that the client can work m er Accept-Encoding cia l, n Description media compression that the client can handle. character that the Accept-Charset tf or co No client prefers. language Accept-Language that the client prefers ('en' for English). Host http://i-tronics.blogspot.com/ on ly types of host to 240 which a request is being made. Some that servers maintain rely multiple virtual heavily on this header. Referer tio User-Agent from which a request being made. is fo re du ca Information about the client type version. and followed by the entity body. An entity body consists of any data to be sent to the in a query string. Listing 13.2 shows a request sent to a server by Netscape 4.6. Listing 13.2: Typical Client Headers Sent by a Netscape Browser GET / HTTP/1.0 Referer: php http://8080-zink.demon.co.uk.proxy.lib.uiowa.edu/matt/php-book/network/test2. No User-Agent: Mozilla/4.6 tf Connection: Keep-Alive (X11; I; Linux 2.2.6-15apmac ppc) Host: www.corrosive.co.uk Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, image/png, */* Accept-Encoding: gzip Accept-Language: en Accept-Charset: iso-8859-1,*,utf-8 or co m er cia l, server. This is usually a set of URL-encoded name/value pairs similar to those found http://i-tronics.blogspot.com/ us is sent to the server. For requests made using the POST method, an empty line is e For GET and HEAD methods, the header section ends the request, and an empty line n The document on ly servers 241 The Response After a server has received a client's request, it sends a response back to the client. A status line A header section An entity body As you can see, there's a lot of symmetry between a request and a response. In fact, information about an entity body. The status line consists of the HTTP version that the server is using (HTTP/1.0 or HTTP/1.1), a response code, and a text message that clarifies the meaning of the response code. There are many response codes that a server can send to a browser. Each code 13.3 lists some of the more common response codes. Table 13.3: Some Response Codes Code 200 cia l, us e provides some information about the success or otherwise of the request. Table fo re du ca Text OK Moved Permanently Moved Temporarily certain headers can be sent by either client or server, especially those that provide tio The and exists server. m er was successful, the requested data will follow. The requested data no longer on the A No tf or 301 co location header will contain a new address. 302 The requested data has been http://i-tronics.blogspot.com/ n Description request on ly The response usually consists of three parts: 242 moved. A location header will contain a new address. 404 Not Found The data could the address. 500 Internal Server Error fo re du ca in to and in an tio data. CGI script has encountered a severe problem attempting serve the A typical response line, therefore might look something like the following: The header section includes a series of response headers, formatted in the same way as request headers. Table 13.4 lists some headers commonly sent by servers. Table 13.4: Some Common Server Headers Name Date Description current Server co m er cia l, The date The name version tf Content-Type or The MIME type of content the entity body The size of the entity in bytes No Content-Length Location The full address of http://i-tronics.blogspot.com/ us e HTTP/1.1 200 OK server n The server or a on ly supplied not be found at 243 alternative document After the headers have been sent, the server sends an empty line to the client followed by the entity body (the document originally requested). Listing 13.3 shows a typical server response. Listing 13.3: A Server Response 1: HTTP/1.1 200 OK 2: Date: Sun, 30 Jan 2000 18:02:20 GMT 3: Server: Apache/1.3.9 (UNIX) 4: Connection: close 5: Content-Type: text/html 6: 7: <html> 8: <head> 9: <title>Listing 13.3 A server response</title> 10: </head> 11: <body> 12: Hello 13: </body> 14: </html> Getting a Document from a Remote Address remote servers and making the output available to your scripts. If you are already acquire information from the Web. In fact, the syntax is exactly the same. You can use fopen() to connect to a Web address in the same way as you would with a file. No Listing 13.4 opens a connection to a remote server and requests a page, printing the result to the browser. 1: <html> 2: <head> 3: <title>Listing 13.4 Getting and printing a web page with fopen()</title> 4: </head> Listing 13.4: Getting and Printing a Web Page with fopen() tf or comfortable reading files from the server, you will have no problem using PHP to co Although PHP is a server-side language, it can act as a client, requesting data from m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 244 5: <body> 6: <?php 7: $webpage = "http://80-www.corrosive.co.uk.proxy.lib.uiowa.edu/php/hello.html"; 8: $fp = fopen( $webpage, "r" ) or die("couldn't open $webpage"); 9: while ( ! feof( $fp )) 10: 11: ?> 12: </body> 13: </html> print fgets( $fp, 1024 ); on the page we include are "broken." This is because paths to images in IMG elements are often relative. When our script outputs the data it has downloaded, the user's browser will look on our server for the images referenced. We could work around this problem to some extent by adding the following tag to the HEAD element of our script: <base href="http://www.php.net"> fopen() returns a file pointer if the connection is successful and false if the pointer, you can use it as normal to read the file. PHP introduces itself to the remote server as a client. On my system, it sends the following request: Host: www.php.net GET / HTTP/1.0 User-Agent: PHP/4.0b3 This process is simple and is the approach you will use to access a Web page in most instances. You might want to connect to other network services, however, or learn more about a Web document by parsing the server headers. You will look at how to do this later in the hour. No Converting IP Addresses and Hostnames Even if your server does not provide you with a $REMOTE_HOST variable, you will probably know the IP address of a visitor from the $REMOTE_ADDR environmental variable. You can use this in conjunction with the function gethostbyaddr() to get the user's hostname. gethostbyaddr() requires a string representing an IP address. It returns the equivalent hostname. If an error occurs, it returns the IP address it tf or co m er cia l, connection cannot be established or the page doesn't exist. After you have a file http://i-tronics.blogspot.com/ us commonly, you would parse the document you download. e It is unlikely that you will want to output an entire page to the browser. More fo re du ca When this script is run, you should see the PHP homepage. Notice that the images tio n on ly 245 was given. Listing 13.5 creates a script that uses gethostbyaddr() to acquire the user's hostname if the $REMOTE_HOST variable is not available. Listing 13.5: Using gethostbyaddr() to Get a Hostname 1: <html> 2: <head> 3: <title>Listing 13.5 Using gethostbyaddr() to get a host name</title> 4: </head> 5: <body> 6: <?php 7: if ( isset( $REMOTE_HOST ) ) 8: 10: 11: else 12: 13: ?> 14: </body> 15: </html> print "Hello visitor at $REMOTE_HOST<br>"; 9: elseif ( isset ( $REMOTE_ADDR ) ) print "Hello visitor at ".gethostbyaddr( $REMOTE_ADDR )."<br>"; print "Hello you, wherever you are<br>"; browser. Otherwise, if we have access to the $REMOTE_ADDR variable, we attempt generic welcome message. To attempt to convert a hostname to an IP address, you can use gethostbyname(). error occurs, the hostname you provided. Making a Network Connection a remote server as simple as opening a file on your own system. Sometimes, though, No you need to exercise a little more control over a network connection or acquire more information about it. You can make a connection to an Internet server with fsockopen(), which requires a hostname or IP address, a port number, and two reference variables. Remember that you can pass a reference to a variable by prepending an ampersand (&) symbol. The reference variables you passed to fsockopen() are populated to provide more tf So far we have had it easy. This is because PHP makes working with a Web page on or co m er This function requires a hostname as its argument. It returns an IP address or, if an cia l, to acquire the user's hostname using gethostbyaddr(). If all else fails, we print a http://i-tronics.blogspot.com/ us If we have access to the $REMOTE_HOST variable, we simply print this to the e fo re du ca tio n on ly 246 information about the connection attempt should it fail. You can also pass fsockopen() an optional timeout integer, which determines how long fsockopen() will wait (in seconds) before giving up on a connection. If the connection is successful, a file pointer is returned. Otherwise, it returns false. The following fragment initiates a connection to a Web server: $fp = fsockopen( "www.corrosive.co.uk", 80, &$errno, &errdesc, 30 ); 80 is the usual port number that a Web server listens on. The first reference variable, $errno, contains an error number if the connection is unsuccessful, and $errdesc might contain more information about the failure. After you have the file pointer, you can both write to the connection with fputs() and read from it with fgets() as you might with a file. When you have finished working with your connection, you should close it with fclose(). We now have enough information to initiate our own connection to a Web server. Listing 13.6 makes an HTTP connection, retrieving a page and storing it in a variable. Listing 13.6: Retrieving a Web Page Using fsockopen() 1: <html> 2: <head> 3: <title>Listing 13.6 Retrieving a Web page using fsockopen()</title> 4: </head> 5: <body> 6: <?php 7: $host = "www.corrosive.co.uk"; No 10: if ( ! $fp ) 11: die ( "Couldn't connect to $host:\nError: $errno\nDesc: $errdesc\n" ); 12: 13: $request = "GET $page HTTP/1.0\r\n"; 14: $request .= "Host: $host\r\n"; tf 9: $fp = fsockopen( "$host", 80, &$errno, &$errdesc); or 8: $page = "/index.html"; co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 247 15: $request .= "Referer: http://80-www.corrosive.co.uk.proxy.lib.uiowa.edu/refpage.html\r\n"; 16: $request .= "User-Agent: PHP test client\r\n\r\n"; 17: $page = array(); 18: fputs ( $fp, $request ); 19: while ( ! feof( $fp ) ) 20: $page[] = fgets( $fp, 1024 ); 24: </html> Notice the request headers that we send to the server. The Webmaster at the remote host will see the value you sent in the User-Agent header in her log file. She http://80-www.corrosive.co.uk.proxy.lib.uiowa.edu/refpage.html. For this reason, you should be cautious of some of the environmental variables available to your scripts. Treat them as an invaluable guide, rather than a set of facts. There are some legitimate reasons why you might want to fake some headers. You browsers. The only way you can do this is to include the word "Mozilla" in the User-Agent header. Nevertheless, pity the poor Webmaster. Operational decisions provide. are made as a result of server statistics, so try not to distort the information you may also assume that a visitor to our page connected from a link at The example in Listing 13.6 adds little to PHP's built-in method of acquiring Web when we request a series of pages. No Listing 13.7: Outputting the Status Lines Returned by Web Servers tf pages. Listing 13.7 uses fsockopen() to check the status codes returned by servers 1: <html> 2: <head> 3: <title>Listing 13.7 Outputting the status lines returned by web servers</ or co m er might need to parse some data that will only be sent to Netscape compatible cia l, http://i-tronics.blogspot.com/ us e fo re du ca 23: </body> tio 22: ?> n 21: fclose( $fp );print "the server returned ".(count($page))." lines!"; on ly 248 title> 4: </head> 5: <body> 6: <?php 7: $to_check = array ( 8: 9: 10: "www.corrosive.co.uk" => "/index.html", => => "/notthere.html", "/nohost.html" "www.virgin.com" "www.4332blah.com" ); 11: foreach ( $to_check as $host => $page ) 12: 13: 14: 15: 16: 17: { $fp = fsockopen( "$host", 80, &$errno, &$errdesc, 10); print "Trying $host<BR>\n"; if ( ! $fp ) { print "Couldn't connect to $host:\n<br>Error: $errno\n<br>Desc: 18: 19: 20: 21: 22: 23: 24: 25: 26: print "<br><hr><br>\n"; continue; } fputs( $fp, "HEAD $page HTTP/1.0\r\n\r\n" ); print "<br><br><br>\n"; No 27: ?> 28: </body> 29: </html> tf or fclose( $fp ); } co print fgets( $fp, 1024 ); m er print "Trying to get $page<br>\n"; cia l, http://i-tronics.blogspot.com/ us $errdesc\n"; e fo re du ca tio n on ly 249 We create an associative array of the server names and page addresses we want to check. We loop through this using a foreach statement. For every element, we initiate a connection using fsockopen(), setting a timeout of 10 seconds. If the connection fails, we print a message to the browser and use continue to move on to the next pair. If the connection is successful, we send a request to the server. We use the HEAD method because we are not interested in parsing an entity body. We use fgets() to get the status line from the server. We are not goin g to work with on to the next element in the list. Figure 13.2 shows the output from Listing 13.7. server headers for this example, so we close the connection with fclose() and move Figure 13.2: A script to print server response headers. Making an NNTP Connection Using fsockopen() fsockopen() can be used to make a connection to any Internet server. In Listing headers of the first message. No tf Listing 13.8: A Basic NNTP Connection Using fsockopen() 1: <html> 2: <head> 3: <title>Listing 13.8 A basic NNTP connection using fsockopen()</title> 4: </head> 5: <body> or 13.8, we connect to an NNTP (Usenet) server, select a newsgroup, and list the co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 250 6: <?php 7: $server = "news"; // change this to your news server 8: $group = "alt.test"; 9: $line = ""; 10: print "<pre>\n"; 11: print "-- Trying to connect to $server\n\n"; 12: $fp = fsockopen( "$server", 119, &$error, &$description, 10 ); 13: if ( ! $fp ) 14: die("Couldn't connect to $server\n$errno\n$errdesc\n\n"); 16: $line = fgets( $fp, 1024 ); 17: $status = explode( " ", $line ); 18: if ( $status[0] != 200 ) 19: 20: 21: 22: { fputs( $fp, "close" ); die("Error: $line\n\n"); } 23: print "$line\n"; 24: print "-- Selecting $group\n\n"; 26: $line = fgets( $fp, 1024 ); 28: if ( $status[0] != 211 ) 29: 30: 31: No 32: 33: print "$line\n"; 34: print "-- Getting headers for first message\n\n"; 35: fputs( $fp, "head\n" ); tf or { fputs( $fp, "close" ); die("Error: $line\n\n"); } co 27: $status = explode( " ", $line ); m er 25: fputs( $fp, "group alt.test\n" ); cia l, http://i-tronics.blogspot.com/ us e fo re du ca 15: print "-- Connected to $server\n\n"; tio n on ly 251 36: $line = fgets( $fp, 1024 ); 37: $status = explode( " ", $line ); 38: print "$line\n"; 39: if ( $status[0] != 221 ) 40: 41: 42: 43: { fputs( $fp, "close" ); die("Error: $line\n\n"); } 44: while ( ! ( strpos($line, ".") === 0 ) ) 45: 46: 47: 48: { $line = fgets( $fp, 1024 ); print $line; } 49: fputs( $fp, "close\n" ); 50: print "</pre>"; 51: ?> 52: </body> 53: </html> The code in Listing 13.8 does little more than demonstrate that an NNTP connection line parsing in a function to save repetition and to extract more information from the server's output. Rather than reinvent the wheel in this way, you might want to investigate PHP's IMAP functions, which will automate much of this work for you. We store the hostname of our server in a variable, $server, and the group we want No to select in $group. If you wish to run this script, you should assign the hostname of your Internet Service Provider's news server to the $server variable. We use fsockopen() to connect to the host on port 119, which is the usual port for NNTP connections. If a valid file pointer is not returned, we use die() to print the error number and description to the browser and end script execution. On connection, the server should have sent us a confirmation message, so we attempt to acquire this with fgets(). If all is well, this string begins with the status code 200. To test this, we tf or co is possible with fsockopen(). In a real-world example, you would want to handle the m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 252 use explode() to split the $line string into an array using the space character as the delimiter. You can learn more about the explode function in Hour 17. If the first element of this array is 200, we can continue; otherwise, we end the script. If all is proceeding as expected, we send the news server the "group" command that should select a newsgroup. If this is successful, the server should return a string don't get what we are expecting. beginning with the status code 211. We test this once again, and end execution if we Now that we have selected our newsgroup, we send the "head" command to the server, which requests the headers for the first message in the group. Again, we test the server response, looking for the status code 221. Finally, we acquire the line, so we test for this in a while statement. As long as the server's output line does not begin with a dot, we request and print the next line. header itself. The server's listing of a header will end with a single dot(.) on its own Finally, we close the connection. Figure 13.3 shows a typical output from Listing 13.8. No Sending Mail with the mail() Function PHP can automate the sending of Internet mail for you. The the message. tf Figure 13.3: Making an NNTP connection. or co m er cia l, us e fo re du ca tio requires three strings representing the recipient of the mail, the mail subject, and mail() returns false if it encounters an error. In the following fragment, we send an email: $to = "someone@adomain.com"; $subject = "hi"; http://i-tronics.blogspot.com/ n mail() on ly function 253 $message = "just a test message! "; mail( $to, $subject, $message ) or print "Could not send mail"; If you are running PHP on a UNIX system, set this using the mail() will use Sendmail. On other systems, the function will connect to a local or remote SMTP mail server. You should SMTP directive in the php.ini file. You are not limited to the mail headers implied by the arguments. You can include as many mail headers as you want in an optional fourth string argument. These should be separated by CRLF characters ('\r\n'). In the following example, we include a From field in our mail message, as well as an $to = "someone@adomain.com"; $from = "book@corrosive.co.uk"; $subject = "hi"; $message = "just a test message! "; or print "Could not send mail"; mail( $to, $subject, $message, "$from\r\nX-Priority: 1 (Highest)" ) In this hour, you learned how to use environmental variables to learn more about your visitors. If you don't have access to a user's hostname, you should now be able to use gethostbyaddr() to acquire it. You learned some of the basics about the negotiation that takes place between client and server when an HTTP connection is made. You learned how to use fopen() to get a document from the Web, and how to use fsockopen() to make connections to other network services. Finally, you learned No Q&A Q HTTP seems a little esoteric. Do I really need to know about it to write good PHP code? A No. You can write excellent code with knowing the intricacies of client/server interaction. On the other hand, a basic understanding of the process is useful if you want to do more than just download pages from remote servers. http://i-tronics.blogspot.com/ tf or how to use mail() to send email from your scripts. co fsockopen() to make your own HTTP connection. You should also be able to use m er cia l, us e Summary fo re du ca tio n X-Priority header that some clients will recognize: on ly mail() function's required 254 Q If I can send fake headers to a remote server, how suspicious should I be of environmental variables myself? A You should not trust environmental variables such as $HTTP_REFERRER and $HTTP_USER_AGENT if their accuracy is essential to the operation of your script. Remember, though, that the vast majority of clients that you deal with will tell you browser type or gathering overall statistical information, there is no need to distrust this data. the truth. If you are merely ensuring a productive user experience by detecting Workshop The Workshop provides quiz questions to help you solidify your understanding of the material covered. Try to understand the quiz answers before continuing to the next hour's lesson. Quiz answers are provided in Appendix A. Quiz across multiple visits to your script? What does HTTP stand for? request? What client header line tells the server about the browser that is making the What does the server response code 404 mean? Without making your own network connection, what function might you use to Given an IP address, what function could you use to get a hostname? What function would you use to make a network connection? What PHP function would you use to send an email? Activities Create access a Web page on a remote server? No tf or co a m er script cia l, that us Why can you not rely on the $REMOTE_ADDR variable to track an individual user accepts e What environmental variable might give you the URL of the referring page? fo re du ca a Web hostname tio (such as http://i-tronics.blogspot.com/ http://www.microsoft.com) from user input. Send the host a HEAD request using fsockopen() to create the connection. Print the response to the browser. Remember to handle the possibility that no connection can be established. n on ly 255 Create a script that accepts a message from the user and mails it to you. Add environmental variables to the user's message to tell you about his or her browser and IP address. No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 256 Hour 14: Working with Dynamic Images Overview The functions included in this hour rely on an open source library called GD. The GD library is a set of tools that enable programmers to create and work with If you have the GD library installed on your system and PHP was compiled to use it, systems will still run the older version of the library, which allows the creation of images in GIF format. Later versions of the library do not support GIFs for licensing reasons. If your system is using a later library, it is possible to compile PHP so that the image functions output images in PNG format, which is supported by the more popular browsers. If you have the GD library, you will be able to use PHP's image functions to create sophisticated graphics on-the-fly. In this hour, you will learn How to create and output an image How to work with colors How to fill areas with color How to draw shapes, including arcs, rectangles, and polygons How to work with TrueType fonts Creating and Outputting Images You can do this using the imagecreate() function. imagecreate() requires two identifier, which you will use with most of the functions that we will cover in this hour. No After you have an image identifier, you are nearly ready to output your first image image identifier as an argument. Listing 14.1 uses these functions to create and to the browser. To do this, you need the imagegif() function, which requires the output an image. Listing 14.1: A Dynamically Created Image 1: <?php tf or arguments, one for the image's height and another for its width. It returns an image co Before you can begin to work with an image, you must acquire an image identifier. m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca you will be able to use PHP's image functions to create dynamic images. Many tio n images on-the-fly. You can find out more about GD at http://www.boutell.com/gd/. on ly 257 2: header("Content-type: image/gif"); 3: $image = imagecreate( 200, 200 ); 4: imagegif($image); 5: ?> Notice that we sent a Content-type header to the browser before doing anything else. We need to tell the browser to expect image information; otherwise, it treats the script's output as HTML. This script can now be called directly by the browser, or <img src="eg14.1.php" alt="a PHP generated image"> Figure 14.1 shows the output of Listing 14.1. We have created a square, but we have no way as yet of controlling its color. Figure 14.1: A dynamically created image. To work with color, you need to acquire a color identifier. You can do this with the No imagecolorallocate() function, which requires an image identifier and three integers between 0 and 255 representing red, green, and blue. The function returns an image identifier that you can use to define the color of shapes, fills, and text. $red = imagecolorallocate($image, 255,0,0); tf or Acquiring Color co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n as part of an IMG element. on ly 258 Coincidentally, the first time you call imagecolorallocate(), you also set the default color for your image; so by adding the previous code fragment to Listing 14.1, we would create a red square. Drawing Lines Before you draw a line on an image, you need to determine the points from and to which you want to draw. You can think of an image as a block of pixels indexed from 0 on both the horizontal and vertical axes. Their origin is the top left-hand corner of the image. ninth pixel down, looking from left to right, top to bottom. requires an image identifier, four integers representing the start and end coordinates of the line, and a color identifier. corner. Listing 14.2 adds to the image created in Listing 14.1, drawing a line from corner to Listing 14.2: Drawing a Line with imageline() 1: <?php 3: $image = imagecreate( 200, 200 ); 5: $blue = imagecolorallocate($image, 0,0,255 ); 6: imageline( $image, 0, 0, 199, 199, $blue ); 8: ?> 7: imagegif($image); We acquire two color identifiers, one for red and one for blue. We then use the identifier stored in the variable $blue for the line's color. Notice that our line ends at 0. Figure 14.2 shows the output from Listing 14.2. the coordinates 199, 199 and not 200, 200. Remember that pixels are indexed from No tf or co m er cia l, 4: $red = imagecolorallocate($image, 255,0,0); http://i-tronics.blogspot.com/ us 2: header("Content-type: image/gif"); e fo re du ca The imageline() function draws a line between one pixel coordinate and another. It tio n In other words, the pixel with the coordinates 5, 8 is the sixth pixel along and the on ly 259 Figure 14.2: Drawing a line with imageline(). Applying Color Fills You can fill an area with color using PHP just as you can with your favorite graphics application. The function imagefill() requires an image identifier, starting starting pixel and all adjacent pixels of the same color. Listing 14.3 adds a call to imagefill() to our script, making the image a little more interesting. Listing 14.3: Using imagefill() 1: <?php coordinates for the fill it is to perform, and a color identifier. It then transforms the 3: $image = imagecreate( 200, 200 ); 4: $red = imagecolorallocate($image, 255,0,0); 5: $blue = imagecolorallocate($image, 0,0,255 ); 6: imageline( $image, 0, 0, 199, 199, $blue ); 7: imagefill( $image, 0, 199, $blue ); 9: ?> 8: imagegif($image); No Figure 14.3 shows the output from Listing 14.3. tf or co m er 2: header("Content-type: image/gif"); cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 260 Figure 14.3: Using imagefill(). Drawing an Arc You can add partial or complete arcs to your images with the imagearc() function. imagearc() requires an image object, coordinates for the center point, an integer for identifier. Arcs are drawn clockwise starting from 3 o'clock. The following fragment draws a quarter circle: imagearc( $image, 99, 99, 200, 200, 0, 90, $blue ); This draws a partial arc, with its center at the coordinates 99, 99. The total height and width will both be 200 pixels. Drawing starts at 3 o'clock and continues for 90 Listing 14.4 draws a complete circle and fills it with blue. Listing 14.4: Drawing a Circle with imagearc() 1: <?php degrees (to 6 o'clock). width, an integer for height, a start point and an end point (in degrees), and a color 2: header("Content-type: image/gif"); No tf 3: $image = imagecreate( 200, 200 ); 5: $blue = imagecolorallocate($image, 0,0,255 ); 6: imagearc( $image, 99, 99, 180, 180, 0, 360, $blue ); 7: imagefill( $image, 99, 99, $blue ); 8: imagegif($image); 9: ?> 4: $red = imagecolorallocate($image, 255,0,0); or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 261 Figure 14.4 shows the output from Listing 14.4. Figure 14.4: Drawing a circle with imagearc(). Drawing a Rectangle You can draw a rectangle in PHP fo re du ca using the imagerectangle() function. top-left corner, the coordinates for its bottom-right corner, and a color identifier. bottom-right coordinates are 179, 179: imagerectangle( $image, 19, 19, 179, 179, $blue ); however, PHP provides the imagefilledrectangle() function, which expects exactly the same arguments as imagerectangle() but produces a rectangle filled with the color you specify. Listing 14.5 creates a filled rectangle and outputs the image to the browser. Listing 14.5: Drawing a Filled Rectangle with imagefilledrectangle() 1: <?php You could then fill this with imagefill(). Because this is such a common operation, No 2: header("Content-type: image/gif"); 3: $image = imagecreate( 200, 200 ); 4: $red = imagecolorallocate($image, 255,0,0); 5: $blue = imagecolorallocate($image, 0,0,255 ); 6: imagefilledrectangle( $image, 19, 19, 179, 179, $blue ); 7: imagegif( $image ); tf or co m er cia l, The following fragment draws a rectangle whose top-left coordinates are 19, 19 and http://i-tronics.blogspot.com/ us imagerectangle() requires an image identifier, the coordinates for your rectangle's e tio n on ly 262 8: ?> Figure 14.5 shows the output from Listing 14.5. Figure 14.5: Drawing a filled rectangle with imagefilled-rectangle(). You can draw more sophisticated shapes using imagepolygon(). This function the number of points in the shape, and a color identifier. The array passed to imagepolygon() should be numerically indexed. The first two elements give the point, and so on. imagepolygon() fills in the lines between the points, automatically closing your shape by joining the final point to the first. You can create a filled polygon with the imagefilledpolygon() function. Listing 14.6 draws a filled polygon, outputting the result to the browser. Listing 14.6: Drawing a Polygon with imagefilledpolygon() coordinates of the first point, the second two give the coordinates of the second No tf 1: <?php 2: header("Content-type: image/gif"); 3: $image = imagecreate( 200, 200 ); 5: $blue = imagecolorallocate($image, 0,0,255 ); 6: $points = array ( 7: 190, 190, 10, 10, 4: $red = imagecolorallocate($image, 255,0,0); or co m er cia l, requires an image identifier, an array of point coordinates, an integer representing http://i-tronics.blogspot.com/ us Drawing a Polygon e fo re du ca tio n on ly 263 8: 9: 10: 190, 10, 10, 190 ); 11: imagefilledpolygon( $image, $points, count( $points )/2 , $blue ); 12: imagegif($image); 13: ?> Notice that to tell imagefilledpolygon() how many points we want to connect, we 14.6 shows the output from Listing 14.6. PHP allows you to make selected colors within your image transparent with imagecolortransparent(). This function requires an image identifier and a color identifier. When you output your image to the browser, the color you pass to so that the shape "floats" on the browser instead of sitting against a background color. Listing 14.7: Making Colors Transparent with imagecolortransparent() 1: <?php 2: header("Content-type: image/gif"); 3: imagecolortransparent() will be transparent. Listing 14.7 changes our polygon code No tf or co Making a Color Transparent m er Figure 14.6: Drawing a polygon with imagefilled-polygon(). cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n count the number of elements in the $points array and divide the result by 2. Figure on ly 264 4: $image = imagecreate( 200, 200 ); 5: $red = imagecolorallocate($image, 255,0,0); 6: $blue = imagecolorallocate($image, 0,0,255 ); 7: 8: $points = array ( 9: 10: 11: 12: 13: 15: imagecolortransparent( $image, $red ); 16: imagegif($image); 17: ?> 190, 190, 190, 10, 10, 190 ); 10, 10, 14: imagefilledpolygon( $image, $points, count( $points )/2 , $blue ); Figure 14.7 shows the output from Listing 14.7. No Working with Text If you have TrueType fonts on your system, you can use these to write text into your images. In addition to the GD library, you need to have the FreeType library installed on your system. If you have this combination, you can create image-based tf Figure 14.7: Making colors transparent with image-colortransparent(). or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 265 charts or navigation elements. PHP even gives you the tool you need to check that any text that you write will fit within the space available. Writing a String with imageTTFtext() eight arguments: an image identifier, a size argument representing the height of the characters to be written, an angle, the starting coordinates (one argument for and the text you want to write. character in the string will be. Listing 14.8 writes a string to an image and outputs the result to the browser. Listing 14.8: Writing a String with imageTTFtext() 1: <?php 2: header("Content-type: image/gif"); 3: 5: $red = imagecolorallocate($image, 255,0,0); 6: $blue = imagecolorallocate($image, 0,0,255 ); 7: $font = "/usr/local/jdk121_pre-v1/jre/lib/fonts/LucidaSansRegular.ttf"; 8: 9: imageTTFtext( $image, 50, 0, 20, 100, $blue, $font, "Welcome!" ); No 12: ?> We create a canvas with a width of 400 pixels and a height of 200 pixels. We define two colors and store the path to a TrueType font in a variable called $font. Note that font files are likely to be stored in a different directory on your server. If you are not tf 11: imagegif($image); or 10: co m er cia l, 4: $image = imagecreate( 400, 200 ); http://i-tronics.blogspot.com/ us e fo re du ca The start point for any text you write determines where the baseline of the first tio n the x axis and another for the y axis), a color identifier, the path to a TrueType font, on ly You can write text to your image with the imageTTFtext() function. This requires 266 sure where, you could try searching for files with the .ttf extension. We then write the text "Welcome!" to the image. For the call to imageTTFtext(), we define a size of 50, an angle of 0, a starting position of 20 on the x axis and 100 on the y axis. We also pass the function the color identifier stored in the $blue variable, the font path stored in $font, and, finally, the text we want to output. You can see the result in Figure 14.8. Figure 14.8: Writing text with imageTTFtext(). argument does not give us an accurate idea of the text's height, and the width is a mystery. In fact, imageTTFtext() will return dimension information, but by then the deed is done. Luckily, PHP provides a function that allows you to try before you buy. Testing Text Dimensions with imageTTFbox() imageTTFbox() requires the font size, the angle, a path to a font file, and the text to No be written. It is one of the few image functions that do not require an image identifier. It returns an eight-element array, which is explained in Table 14.1. Table 14.1: The Array Returned by imageTTFbox() Index 0 Description bottom left tf function, which is so called because it tells you about the text's bounding box. or You can get information about the dimensions of text using the imageTTFbox() co m er cia l, Of course, we have to guess where to put the text at the moment. The size http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 267 (horizontal axis) 1 bottom left (vertical axis) 2 bottom (horizontal axis) 3 bottom right right (horizontal axis) 5 top right (vertical axis) 6 top (horizontal axis) 7 top left left All figures on the vertical axis are relative to the text's baseline, which is 0. Figures are minus numbers. Figures for the vertical axis at the bottom of the text count up from 0, giving the number of pixels the text drops from the baseline. So, if you test a string containing a "y" with imageTTFbbox(), for example, the 3 pixels below the baseline. It could have a figure of − 10 for element 7 because the text is raised 10 pixels above the baseline. No To complicate matters, there seems to be a 2-pixel difference between the baseline as returned by imageTTFbbox() and the visible baseline when drawing text. You may need to adjust for this, by thinking of the height of the baseline as 2 pixels greater than that returned by the imageTTFbbox(). On the horizontal axis, figures for left-hand side imageTTFbbox() will take account of text that begins before the given start point by returning the offset as a minus tf or return array might have a figure of 3 for element 1 because the tail of the "y" drops co m er for the vertical axis at the top of the text count down from this figure, and so usually cia l, (vertical axis) http://i-tronics.blogspot.com/ us e fo re du ca 4 top right tio (vertical axis) n on ly 268 number in elements 6 and 0. This usually will be a small number so whether you adjust alignment to take account of this depends on the level of accuracy you require. You can use the information returned by imageTTFbbox() to align text within an image. Listing 14.9 creates a script that dynamically outputs text, centering it within Listing 14.9: Aligning Text Within a Fixed Space Using imageTTFbbox() our image on both the vertical and horizontal planes. 2: header("Content-type: image/gif"); 3: $height = 100; 4: $width = 200; 5: $fontsize = 50; 6: if ( ! isset ( $text ) ) 7: $text = "Change me!"; 8: $image = imagecreate( $width, $height ); 10: $blue = imagecolorallocate($image, 0,0,255 ); 11: $font = "/usr/local/jdk121_pre-v1/jre/lib/fonts/LucidaSansRegular.ttf"; 12: $textwidth = $width; 13: $textheight; 14: while ( 1 ) 15: 16: 17: 18: { $box = imageTTFbbox( $fontsize, 0, $font, $text ); or $textwidth = co No 19: 20: 21: tf $textbodyheight = ( abs($box[7]) )− 2; if ( $textwidth < $width − 20 ) break; $fontsize− − ; } 22: 23: $gifXcenter = (int) ( $width/2 ); m er cia l, abs( $box[2] ); http://i-tronics.blogspot.com/ us 9: $red = imagecolorallocate($image, 255,0,0); e fo re du ca tio n 1: <?php on ly 269 24: $gifYcenter = (int) ( $height/2 ); 25: imageTTFtext( 26: 27: 28: $image, $fontsize, 0, (int) ($gifXcenter− ($textwidth/2)), (int) ($gifYcenter+(($textbodyheight)/2) ), $blue, $font, $text ); 29: imagegif($image); 30: ?> set a default font size of 50. We test for the presence of a variable called $text, setting a default if it isn't present. In this way, the image can accept data from a Web page, either in the query string of an image URL or from form submission. We use imagecreate() to acquire an image identifier. We acquire color identifiers in the usual way and store the path to a TrueType font file in a variable called $font. We want to fit the string stored in $text into the available space, but we have no way string to imageTTFbbox(), storing the resultant array in a variable called $box. The axis. We take this to be the width of the string and store it in $textwidth. We want to vertically center the text, but only accounting for the area above the text's baseline. We can use the absolute value of $box[7] to find the height of the text above the baseline, although we need to adjust this by 2 pixels. We store this value in $textbodyheight. Now that we have a working figure for the text's width, we can test it against the width of the image (less 10 pixels border). If the text is smaller than the width of the ready to try again. Dividing the $height and $width values by 2, we can find the approximate center point of the image. We write the text to the image, using the figures we have calculated for the image's center point in conjunction with the text's height and width to calculate the offset. canvas we are using, then we end the loop. Otherwise, we reduce the font size, No tf or co m er cia l, element $box[2] contains the position of the lower-right corner on the horizontal http://i-tronics.blogspot.com/ us of knowing yet whether it will. Within a while statement, we pass the font path and e fo re du ca We store the height and width of the image in the variables $height and $width, and tio n on ly 270 Finally, we write the image to the browser. Figure 14.9 shows the output from Listing 14.9. This code can now be called from another page as part of an IMG element. The following fragment writes some simple code that would allow a user to add her own string to be included in the image: 1: <?php 2: if ( ! isset( $text ) ) 3: 4: ?> $text = "Dynamic text!"; 6: <input type="text" name="text"> 7: </form> 8: <p> 9: <img src="eg14.9.php?<? print "text=".urlencode($text) ?>"> When we call the script in Listing 14.9, we append a query string that includes the text to be added to the image. You can learn more about this technique for passing information from script to script in Hour 19, "Saving State with Cookies and Query Strings." No Figure 14.9: Aligning text within a fixed space using imageTTFbbox(). Bringing It Together Let's build an example that uses some of the functions that we have looked at in this tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca 5: <form action="<? print $PHP_SELF >" method="POST"> tio n on ly 271 hour. Suppose that we have been asked to produce a dynamic bar chart that compares a range of labeled numbers. The bar chart must include the relevant label below each bar. Our client must be able to change the number of bars on the chart, the height and width of the image, and the size of the border around the chart. The bar chart will be used for consumer votes, and all that is needed is an "at a glance" representation of the data. A more detailed breakdown will be included in the HTML portion of the containing page. The easiest way of storing labels and values is in an associative array. After we have this array, we need to calculate the number of bars we will be dealing with and the $cells = array ( liked=>200, hated=>400, indifferent=>900 ); $max = max( $cells ); $total = count ( $cells ); $totalwidth = 400; $totalheight = 200; $xgutter = 20; // left/right margin $ygutter = 20; // top/bottom margin We must set up some variables to allow the client to customize the image: $font = "/usr/local/jdk121_pre-v1/jre/lib/fonts/LucidaSansRegular.ttf"; $xgutter and $ygutter variables determine the margin around the chart horizontally and vertically. $internalgap determines the space between the bars. The of the screen. $bottomspace variable contains the space available to label the bars at the bottom Now that we have these values, we can do some calculations to arrive at some useful variables: $graphCanX = ( $totalwidth − $xgutter*2 ); $graphCanY = ( $totalheight − $ygutter*2 − $bottomspace ); $posY = $totalheight − $ygutter − $bottomspace; // starting draw pos - y - axis $cellwidth = (int) (( $graphCanX − ( $internalgap * No tf $posX = $xgutter; // starting draw position x - axis ( $total− 1 ) )) / $total) ; $textsize = (int)($bottomspace); We calculate the graph canvas (the space in which the bars are to be written). On the x axis, this will be the total width minus twice the size of the margin. On the y axis, we need also to take account of the $bottomspace variable to leave room for the labels. or co m er cia l, The client can change the variables to define the image height and width. The http://i-tronics.blogspot.com/ us $bottomspace = 40; // gap at the bottom (in addition to margin) e $internalgap = 5; // space between cells fo re du ca tio n greatest value in the array: on ly 272 $posX stores the point on the x axis at which we will start drawing the bars, so we set this to the same value as $xgutter, which contains the value for the margin on the $x axis. $posY stores the bottom point of our bars; it is equivalent to the total height of the image less the margin and the space for the labels stored in $bottomheight. $cellwidth contains the width of each bar. To arrive at this value, we must calculate the total amount of space between bars and take this from the chart width, dividing this result by the total number of bars. (as stored in $bottomspace). We initially set the size of the text to be the same as the height left free for label text Before we can create and work with our image, we need to determine the text size. sure that each of the labels will fit within the width of the bar above it. We loop through the $cells array to calculate the maximum text size we can use: while ( list( $key, $val ) = each ( $cells ) ) { while ( 1 ) { $textWidth = $box[2]; break; $textsize− − ; } } if ( $textWidth <$cellwidth ) For each of the elements, we begin a loop, acquiring dimension information for the label using imageTTFbbox(). We take the text width to be $box[2] and test it against the $cellwidth variable, which contains the width of a single bar in the chart. We break the loop if the text is smaller than the bar width; otherwise, we decrement $textsize and try again. $textsize continues to shrink until every label in the array Now, at last we can create an image identifier and begin to work with it: fits within the bar width. No $image = imagecreate( $totalwidth, $totalheight ); $red = ImageColorAllocate($image, 255, 0, 0); $blue = ImageColorAllocate($image, 0, 0, 255 ); $black = ImageColorAllocate($image, 0, 0, 0 ); reset ($cells); while ( list( $key, $val ) = each ( $cells ) ) tf or co m er cia l, http://i-tronics.blogspot.com/ us e $box = ImageTTFbBox( $textsize, 0, $font, $key ); fo re du ca Our problem is that we don't know how long the labels will be, and we want to make tio n on ly 273 { $cellheight = (int) (($val/$max) * $graphCanY); $center = (int)($posX+($cellwidth/2)); imagefilledrectangle( $image, $posX, ($posY− $cellheight), ($posX+$cellwidth), $posY, $blue ); $box = ImageTTFbBox( $textsize, 0, $font, $key ); $tw = $box[2]; ImageTTFText( $image, $textsize, 0, ($center− ($tw/2)), ($totalheight− $ygutter), $black, $font, $key ); $posX += ( $cellwidth + $internalgap); } imagegif( $image ); We begin by creating an image identifier with imagecreate() and allocate some colors. Once again, we loop through our $cells array. We calculate the height of the bar, storing the result in $cellheight. We calculate the center point (on the x axis) of the bar, which is $posX plus half the width of the bar. $cellheight, and $cellwidth. We draw the bar, using imagefilledrectangle() and the variables $posX, $posY, To align our text, we need imageTTFbbox() once again, storing its return array in $tw. We now have enough information to write the label. We derive our x position the image's height minus the margin. Finally, we output the image. We increment $posX ready to start working with the next bar. You can see the complete script in Listing 14.10 and sample output in Figure 14.10. Listing 14.10: A Dynamic Bar Chart 1: <?php 2: header("Content-type: image/gif"); No 10: $internalgap = 10; // space between cells tf 3: $cells = array ( liked=>200, hated=>400, indifferent=>900 ); 4: $max = max( $cells ); 5: $total = count ( $cells ); 6: $totalwidth = 300; 7: $totalheight = 200; 8: $xgutter = 20; // left/right margin 9: $ygutter = 20; // top/bottom margin or co m er cia l, from the $center variable minus half the width of the text, and our y position from http://i-tronics.blogspot.com/ us $box. We use $box[2] as our working width and assign this to a temporary variable, e fo re du ca tio n on ly 274 11: $bottomspace = 30; // gap at the bottom (in addition to margin) 12: $font = "/usr/local/jdk121_pre-v1/jre/lib/fonts/LucidaSansRegular.ttf"; 13: $graphCanX = ( $totalwidth − $xgutter*2 ); 14: $graphCanY = ( $totalheight − $ygutter*2 − $bottomspace );// starting draw position x - axis 15: $posX = $xgutter; // starting draw pos - y - axis 16: $posY = $totalheight − $ygutter − $bottomspace; 17: $cellwidth = (int) (( $graphCanX − / $total) ; 18: $textsize = (int)($bottomspace); 19: // adjust font size 20: while ( list( $key, $val ) = each ( $cells ) ) 21: 22: 23: 24: 25: 26: 27: 28: 29: 30: } } { while ( 1 ) { ( $internalgap * ( $total− 1 ) )) $box = ImageTTFbBox( $textsize, 0, $font, $key ); $textWidth = abs( $box[2] ); if ( $textWidth < $cellwidth ) break; $textsize− − ; 31: $image = imagecreate( $totalwidth, $totalheight ); 32: $red = ImageColorAllocate($image, 255, 0, 0); 34: $black = ImageColorAllocate($image, 0, 0, 0 ); 35: $grey = ImageColorAllocate($image, 100, 100, 100 ); 36: reset ($cells); 38: 39: 40: 41: 42: 43: 44: 45: 37: while ( list( $key, $val ) = each ( $cells ) ) 33: $blue = ImageColorAllocate($image, 0, 0, 255 ); or { co m er cia l, No tf $cellheight = (int) (($val/$max) $center = (int)($posX+($cellwidth/2)); imagefilledrectangle( $image, $posX, ($posY− $cellheight), ($posX+$cell width), $posY, $blue ); $box = ImageTTFbBox( $textsize, 0, $font, $key ); $tw = $box[2]; ImageTTFText( $image, $textsize, 0, ($center− ($tw/2)), ($totalheight− $ygutter), $black, $font, $key ); http://i-tronics.blogspot.com/ us e fo re du ca * $graphCanY); tio n on ly 275 46: 47: 49: ?> $posX += ( $cellwidth + $internalgap); } 48: imagegif( $image ); Summary navigation elements with relative ease. In this hour, you learned how to use imagecreate() and imagegif() to create and output an co image. m er PHP's support for the GD library enables you to produce dynamic charts and cia l, You learned us Figure 14.10: A dynamic bar chart. e how fo re du ca to acquire color identifiers with imagecolorallocate() and to use color identifiers with imagefill() to fill areas with color. You learned how to use line and shape functions to create outline and filled TrueType fonts, and worked through an example that wrote text to an image. Finally, you worked through a bar chart example that brought some of these techniques together into a single script. No Q&A Q Are there any performance issues with regard to dynamic images? tf shapes. You learned how to use PHP's support for the FreeType library to work with or http://i-tronics.blogspot.com/ tio n on ly 276 A A dynamically created image will be slower to arrive at the browser than an image that already exists. Depending on the efficiency of your script, the impact is not likely to be noticeable to the user if you use dynamic images sparingly. Workshop The Workshop provides quiz questions to help you solidify your understanding of the material covered. Try to understand the quiz answers before continuing to the next hour's lesson. Quiz answers are provided in Appendix A. What header should you send to the browser before building and outputting a GIF image? other image functions? What function would you use to acquire an image identifier that you can use with What function would you use to output your GIF after building it? With which function would you draw a line on a dynamic image? What function would you use to fill an area in a dynamic image? How might you draw a rectangle? How would you draw a polygon? FreeType library)? Activities What function might you use to draw an arc? What function would you use to write a string to a dynamic image (utilizing the Write a script that creates a "progress bar" such as might be used on a No tf fund-raising site to indicate how much money has been raised in relation to the target. Write a script that writes a headline image based on input from a form or query string. Allow user input to determine the canvas size, background and foreground colors, and the presence and offset of a drop shadow. or co m er cia l, http://i-tronics.blogspot.com/ us e What function could you use to acquire a color identifier? fo re du ca Quiz tio n on ly 277 Hour 15: Working with Dates Overview Dates are so much part of everyday life that it becomes easy to work with them without thinking. The quirks of our calendar can be difficult to work with in programs, though. Fortunately, PHP provides powerful tools for date arithmetic that make manipulating dates easy. In this chapter, you will learn How to get information about a date How to format date information How to test dates for validity How to set dates How to build a simple calendar script How to acquire the current date and time is a little hard on the eyes, for us humans, but extremely useful nonetheless. print time(); // sample output: 948316201 The integer returned by midnight GMT on January 1, 1970. This moment is known as the UNIX epoch, and the number of seconds that have elapsed since then is referred to as a time stamp. PHP offers excellent tools to convert a time stamp into a form that humans are comfortable with. Even so, isn't a time stamp a needlessly convoluted way of storing enormous amounts of information. Even better, a time stamp can make date arithmetic much easier than you might imagine. Think of a homegrown date system in which you record days of the month, as well as months and years. Now imagine a script that needs to add one day to a given date. If this date happened to be 31 December 1999, rather than add 1 to the date, you would have to write code to set the day of the month to 1, the month to January, and the year to 2000. Using a time stamp, you need only add a day's worth of seconds to your current figure, and you are done. You can convert this new figure http://i-tronics.blogspot.com/ No tf a date? In fact, the opposite is true. From just one number, you can extract or co m er cia l, current date and time. It requires no arguments but returns an integer. This number time() represents the number of seconds elapsed since us Getting the Date with time() PHP's time() function gives you all the e fo re du ca information that you need about the tio n on ly 278 into something more friendly at your leisure. Converting a Time Stamp with getdate() Now that you have a time stamp to work with, you must convert it before you present it to the user. getdate() optionally accepts a time stamp and returns an associative array containing information about the date. If you omit the time stamp, time(). Table 15.1 lists the elements contained in the array returned by getdate(). it works with the current time stamp as returned by Table 15.1: The Associative Array Returned by getdate() Key seconds Description Example Seconds past the 28 minutes (0– 59) minutes Minutes past the 7 hour (0– 59) hours Hours of the day 12 (0– 23) mday Day of the month 20 (1– 31) (0– 6) mon (1– 12) year yday Year (4 digits) Day of month No 0 tf or co weekday m er (0– 365) Day of the week Thursday (name) Month of the year January (name) 948370048 to extract information from a time stamp, using a Figure Timestamp Listing 15.1 uses getdate() foreach statement to print each element. You can see a typical output in 15.1. getdate() returns the date according to the local time zone. Listing 15.1: Acquiring Date Information with getdate() 1: <html> cia l, Month of the year 1 year 19 http://i-tronics.blogspot.com/ us wday Day of the week 4 2000 e fo re du ca tio n on ly 279 2: <head> 3: <title>Listing 15.1 Acquiring date information with getdate()</title> 4: </head> 5: <body> 6: <?php 7: $date_array = getdate(); // no argument passed so today's date will be used 8: foreach ( $date_array as $key => $val ) 9: 10: 11: 12: ?> 13: <hr> 14: <? $date_array[year]<p>"; 16: ?> 17: </body> 18: </html> { print "$key = $val<br>"; } 15: print "Today's date: $date_array[mday]/$date_array[mon]/ function returns a formatted string representing a date. You can exercise an enormous amount of control over the format that cia l, Converting a Time Stamp with date() You can use getdate() when you want to work with the elements that it outputs. Sometimes, though, you only want to display the date as a string. The date() us e No Figure 15.1: Using getdate(). In addition to the format string, tf or co m er argument that you must pass to it. date() http://i-tronics.blogspot.com/ fo re du ca date() returns with a string optionally accepts a time stamp. Table tio n on ly 280 15.2 lists the codes that a format string can contain. Any other data you include in the format string passed to date() will be included in the return value. Example 'pm' pm Table 15.2: Format Codes for Use with date() Format a Description 'am' or A 'AM' or 'PM' PM uppercase d Day of month 20 with leading zeroes) D Day of week (three Thu letters) F h Month name Hour zeroes) H Hour zeroes) g Hour (24-hour 12 January (12-hour 12 format— leading format— leading format— no zeroes) Hour G i j co m er format— no zeroes) Minutes No 1 tf or Day of the month 20 (no leading zeroes) Day of the week Thursday (name) Leap year ('1' for 1 yes, '0' for no) L m Month zeroes) (number— leading cia l, (12-hour 12 leading (24-hour 12 leading of year 01 http://i-tronics.blogspot.com/ us 47 e fo re du ca tio (number n on ly lowercase 281 M Month of year (three Jan letters) n Month of year 1 (number— no leading zeroes) U y Y z Z Time stamp Year (two digits) Year (four digits) 948372444 00 2000 Day of year (0– 365) 19 Offset in seconds 0 from GMT Listing 15.2 puts a few format codes to the test. Listing 15.2: Formatting a Date with date() 1: <html> 2: <head> 4: </head> 5: <body> 6: <?php 3: <title>Listing 15.2 Formatting a date with date()</title> 7: print date("m/d/y G.i:s<br>", time()); 9: print "Today is "; 10: print date("j of F Y, \a\\t g.i a", time()); 12: ?> 14: </html> No Although the format string looks arcane, it is easy to build. If you want to add a string to the format that contains letters that are format codes, you can escape them by placing a backslash (\) in front of them. For characters that become control characters when escaped, you must escape the backslash that precedes them. "\n" should become "\\n", for example, if you want to include an "n" in the format string, date() tf or 13: </body> co 11: // Today is 20 of January 2000, at 1.27 pm returns information according to your local time zone. If you want to m er 8: // 01/20/00 13.27:55 cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly s Seconds of hour 24 282 format a date in GMT, you should use the exactly the same way. gmdate() function, which works in Creating Time Stamps with mktime() with arbitrary dates. mktime() returns a time stamp that you can then use with date() or getdate(). mktime() accepts up to six integer arguments in the hour minute second month day of month year following order: Listing 15.3 uses mktime() to get a time stamp that we then use with the date() function. Listing 15.3: Creating a Time Stamp with mktime() 1: <html> 2: <head> 3: <title>Listing 15.3 Creating a timestamp with mktime()</title> 4: </head> 5: <body> 6: <?php 7: // make a timestamp for 1/5/99 at 2.30 am 8: $ts = mktime( 2, 30, 0, 5, 1, 1999 ); No 10: // 05/01/99 2.30:00 11: print "The date is "; 12: print date("j of F Y, \a\\t g.i a", $ts ); 13: // The date is 1 of May 1999, at 2.30 am 14: ?> tf 9: print date("m/d/y G.i:s<br>", $ts); or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly You can already get information about the current time, but you cannot yet work 283 15: </body> 16: </html> You can choose to omit some or all of the arguments to mktime(), and the value appropriate to the current time will be used instead. mktime() will also adjust for values that go beyond the relevant range, so an hour argument of 25 will translate to 1.00am on the day after that specified in the month, day, and year arguments. You may need to accept date information from user input. Before you work with this date, or store it in a database, you should check that the date is valid. checkdate() accepts three integers: month, day, and year. checkdate() returns true if the month is between 1 and 12, the day is acceptable for the given month and year (accounting for leap years, and the year is between 0 and 32767. Be careful, though, a date may well be valid but not acceptable to other date functions. For example, the following line returns true: checkdate( 4, 4, 1066 ) end up with a time stamp of − 1. As a rule of thumb, do not use mktime() with years below 1902 and be cautious of using date functions with any date before 1970. An Example Let's bring most of these functions together into an example. We are going to build user will be able to select both month and year with pull-down menus, and the dates for that month will be organized according to the days of the week. We will use two global variables $month and $year, which should be filled by data by the user. We will use these to build a time stamp based on the first day of the month defined. If the input is invalid or absent, we will default to the first day of the current month. No tf a calendar that can display the dates for any month between 1980 and 2010. The or co m er cia l, If you were to attempt to build a date with mktime() using these values, you would http://i-tronics.blogspot.com/ us e fo re du ca tio Testing a Date with checkdate() n on ly 284 Checking User Input When the user comes to our page for the first time, he or she will not be submitting any information. We must therefore make sure that our script can handle the fact function for this. isset() returns false if the variable it has been passed has not been that the $month and $year variables may not be defined. We could use the isset() defined. However, we choose instead to use checkdate(). Listing 15.4 shows the stamp based on them. Listing 15.4: Checking User Input for the Calendar Script 1: <?php 2: if ( ! checkdate( $month, 1, $year ) ) 3: 4: 5: 6: 7: { $nowArray = getdate(); $month = $nowArray[mon]; $year = $nowArray[year]; } 8: $start = mktime ( 0, 0, 0, $month, 1, $year ); 9: $firstDayArray = getdate($start); 10: ?> Listing 15.4 is a fragment of a larger script so it does not produce any output itself. In our if statement, we use checkdate() to test the $month and $year variables. If valid date from undefined month and year arguments. This approach has the added bonus of ensuring that data that has been submitted by the user will make a valid date. they have not been defined, checkdate() returns false because you cannot make a No If the date is not valid, we use getdate() to create an associative array based on the current time. We then set values for $month and $year ourselves, using the array's mon and year elements. tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n fragment of code that checks the $month and $year variables and builds a time on ly 285 Now that we are sure that we have valid data in $month and $year, we can use mktime() to create a time stamp for the first day of the month. We will need information about this time stamp later on, so we create a variable called $firstDayArray that will store an associative array returned by getdate() and based on this time stamp. Building the HTML Form HTML, we must also ensure that the pull-downs default to the currently chosen month, so we will dynamically create these pull-downs, adding a SELECT attribute to the OPTION element where appropriate. The form is generated in Listing 15.5. Listing 15.5: Building the HTML Form for the Calendar Script 1: <?php 2: if ( ! checkdate( $month, 1, $year ) ) 3: 4: 5: 6: 7: { $nowArray = getdate(); $year = $nowArray[year]; 8: $start = mktime ( 0, 0, 0, $month, 1, $year ); 9: $firstDayArray = getdate($start); 10: ?> No 13: <title><?php print "Calendar: $firstDayArray[month] 14: $firstDayArray[year]" ?></title> 15: <head> 16: <body> 17: <form method="post"> 18: <select name="month"> tf 12: <head> or 11: <html> co m er } cia l, $month = $nowArray[mon]; http://i-tronics.blogspot.com/ us e fo re du ca tio year. For this, we will use SELECT elements. Although we could hard-code these in n We need to create an interface by which users can ask to see data for a month and on ly 286 19: <?php 20: $months = Array("January", "February", "March", "April", 21: 22: "May", "June", "July", "August", "September", "October", "November", "December"); 23: for ( $x=1; $x <= count( $months ); $x++ ) 24: 25: 26: 27: 28: 29: ?> 30: </select> 31: <select name="year"> 32: <?php 33: for ( $x=1980; $x<2010; $x++ ) 34: 35: 36: 37: 38: 39: ?> 40: </select> { print "\t<option"; { print "\t<option value=\"$x\""; print ($x == $month)?" SELECTED":""; print ">".$months[$x− 1]."\n"; } print ($x == $year)?" SELECTED":""; print ">$x\n"; } 41: <input type="submit" value="Go!"> 42: </form> 43: </body> No 44: </html> Having created the $start time stamp and the $firstDayArray date array, we go on to write the HTML for the page. Notice that we use $firstDayArray to add the month and year to the TITLE element. In previous examples we have used the global tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 287 variable $PHP_SELF within the FORM element to ensure that the form will call itself when submitted. In our script we have taken advantage of the fact that leaving the ACTION argument out of a FORM tag will cause the form to submit to its containing page by default. To create the SELECT element for the month pull-down, we drop back into PHP mode to write the individual OPTION tags. First we create an array called $months that contains the 12 month names. We then loop through this, creating an OPTION tag for each one. This would probably be an overcomplicated way of writing a simple SELECT element were it not for the fact that we are testing $x (the counter variable in the for statement) against the $month variable. If $x and that the correct month will be selected automatically when the page loads. We use create a submit button. We should now have a form that can send the month and year parameters to itself, and will default either to the current month and year, or the month and year previously chosen. You can see this in Figure 15.2. Figure 15.2: The calendar form. Creating the Calendar Table No We now need to create a table and populate it with dates for the chosen month. We do this in Listing 15.6, which represents the complete calendar script. Listing 15.6: The Complete Calendar Script tf 1: <?php 2: define("ADAY", (60 *60*24) ); or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca a similar technique to write the year pull-down. Finally, back in HTML mode, we tio n $month are equivalent, we add the string SELECTED to the OPTION tag, ensuring on ly 288 3: if ( ! checkdate( $month, 1, $year ) ) 4: 5: 6: 7: 8: { $nowArray = getdate(); $month = $nowArray[mon]; $year = $nowArray[year]; } 9: $start = mktime ( 0, 0, 0, $month, 1, $year ); 10: $firstDayArray = getdate($start); 11: ?> 12: <html> 13: <head> 14: <title><?php print "Calendar: $firstDayArray[month] 15: 16: <head> 17: <body> $firstDayArray[year]" ?></title> 19: <select name="month"> 20: <?php 21: $months = Array("January", "February", "March", "April", 23: 25: 26: 27: 28: { No 29: 30: ?> 31: </select> 32: <select name="year"> tf or print "\t<option value=\"$x\""; print ($x == $month)?" SELECTED":""; print ">".$months[$x− 1]."\n"; } co 24: for ( $x=1; $x <= count( $months ); $x++ ) m er 22: "May", "June", "July", "August", "September", "October", "November", "December"); cia l, http://i-tronics.blogspot.com/ us 18: <form action="<? print $PHP_SELF ?>" method="post"> e fo re du ca tio n on ly 289 33: <?php 34: for ( $x=1980; $x<2010; $x++ ) 35: 36: 37: 38: 39: 40: ?> 41: </select> 42: <input type="submit" value="Go!"> 43: </form> 44: <p> 45: <?php { print "\t<option"; print ($x == $year)?" SELECTED":""; print ">$x\n"; } 46: $days = Array("Sunday", "Monday", "Tuesday", "Wednesday", 47: "Thursday", "Friday", "Saturday"); 49: foreach ( $days as $day ) 50: print "\t<td><b>$day</b></td>\n"; 51: for ( $count=0; $count < (6 *7); $count++ ) 53: 54: 55: 56: 57: 58: 59: $dayArray = getdate( $start ); tf or No 60: 61: 62: if ( $count < $firstDayArray[wday] || $dayArray[mon] != $month ) { print "\t<td><br></td>\n"; co if ( (($count) % 7) == 0 ) { if ( $dayArray[mon] != $month ) break; print "</tr><tr>\n"; } m er 52: { cia l, http://i-tronics.blogspot.com/ us 48: print "<TABLE BORDER = 1 CELLPADDING=5>\n"; e fo re du ca tio n on ly 290 63: 64: 65: 66: 67: 68: 69: } else { print "\t<td>$dayArray[mday] $dayArray[month]</td>\n"; $start += ADAY; } } 71: ?> 72: </body> 73: </html> 74: Because the table will be indexed by days of the week, we loop through an array of day names, printing each to its own cell. All the real magic of the script happens in the final for statement. iterations. This is to make sure that we will create enough cells to populate with date information. Within the loop, we transform the $start variable into a date array with getdate(), assigning the result to $dayArray. Although $start is the first day of the month during the loop's initial execution, we will increment this time stamp by 24 hours for every iteration. We test the $count variable against 7 using the modulus operator. The block of code multiple of 7. This is our way of knowing whether we should end the loop altogether or start a new row. No After we have established that we are in the first iteration or at the end of a row, we can go on to make another test. If the mon (month number) element of the $dayArray is no longer equivalent to the $month variable, we must have finished. Remember that $dayArray contains information about the $start time stamp, which is in turn our current place in the month that we are displaying. When $start goes beyond the current month, $dayArray[mon] will hold a different figure than the tf or belonging to this if statement will therefore only be run when $count is either 0 or a co m er cia l, We initialize a variable called $count and ensure that the loop will end after 42 http://i-tronics.blogspot.com/ us e fo re du ca tio n 70: print "</tr></table>"; on ly 291 $month number provided by user input. Our modulus test demonstrated that we are at the end of a row, and the fact that we are in a new month means that we can leave the loop altogether. Assuming, however, that we are still in the month that we are displaying, we end the row and start a new one. In the next if statement, we determine whether to write date information to a cell. cell or two. Few months will finish at the end of one of our rows, so it's also likely Not every month begins on a Sunday, so it's likely that we will start with an empty that we will need to write a few empty cells before we close the table. We have stored information about the first day of the month in $firstDayArray; in particular, is smaller than this number, then we know that we haven't yet reached the correct cell for writing. By the same token, if the $month variable is no longer equal to $dayArray[mon], we know that we have reached the end of the month (but not the end of the row, as we determined in our earlier modulus test). In either case, we write an empty cell to the browser. we can access the number of the day of the week in $firstDayArray[wday]. If $count the day number stored in $firstDayArray[wday]. Now we must use the $dayArray and the month name to a cell. Finally, we need to increment the $start variable, which contains our date stamp. We simply add the number of seconds in a day to it (we have defined this value at the top of the script), and we're ready to begin the loop again with a new value in $start to be tested. You can see the output from a call to this script in Figure 15.3. No tf or co m er cia l, associative array that we established early in the loop to write the day of the month http://i-tronics.blogspot.com/ us are within the month that we want to list and that the current day column matches e In the final else clause, we can do the fun stuff. We have already ascertained that we fo re du ca tio n on ly 292 Figure 15.3: The calendar script Summary In this hour, you learned how to use time() to get a date stamp for the current date stamp and date() to convert a time stamp into a formatted string. You learned how to create a time stamp using mktime(). You learned how to test a date for validity some of the tools you have looked at. Q&A The Workshop provides quiz questions to help you solidify your understanding of the material covered. Try to understand the quiz answers before continuing to the next hour's lesson. Quiz answers are provided in Appendix A. Q Are there any functions for converting between different calendars? A Yes. PHP provides an entire suite of functions that cover alternative calendars. You can read about these in the official PHP manual at The Workshop provides quiz questions to help you solidify your understanding of the material covered. Try to understand the quiz answers before continuing to the next hour's lesson. Quiz answers are provided in Appendix A. Quiz No tf How would you acquire a UNIX time stamp representing the current date and time? What function accepts a time stamp and returns an associative array representing the given date? What function would you use to format date information? How would you acquire a time stamp for an arbitrary date? What function could you use to check the validity of a date? http://i-tronics.blogspot.com/ or co m er Workshop cia l, http://www.php.net/manual/ref.calendar.php. us e fo re du ca tio n with checkdate(). Finally, you worked through an example script, which applies on ly and time. You learned how to use getdate() to extract date information from a time 293 Activity Create a birthday countdown script. Given form input of month, day, and year, output a message that tells the user how many days, hours, minutes, and seconds until the big day. No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 294 Hour 16: Working with Data Overview In this hour, we are going to delve a little deeper into data testing and manipulation. an understanding of how data is handled in your scripts is essential if you are to We will look again at data types. PHP handles data types for you automatically, but the more advanced features that PHP provides to manipulate and sort these data In this hour, you will learn How to convert data from one type to another More ways of testing data types How PHP automatically converts data for you in expressions Why an understanding of data types can be useful Another method of traversing an array How to check that an element exists in an array How to custom sort arrays Data Types Revisited There is a little more ground to cover, however. This section examines a few more which PHP automatically converts data types for you. No A Recap You already know that PHP variables can contain values that are integers, doubles, strings, booleans, objects, or arrays. You can test the type of any variable with the gettype() function. gettype() requires a value of any type, and returns a string describing the value's data type: tf or functions for checking the data type of a variable and looks at the conditions under co You learned about PHP's data types in some detail in Hour 4, "The Building Blocks." m er cia l, How to transform every element in an array http://i-tronics.blogspot.com/ us e How to test whether a variable has been set fo re du ca types. tio build robust online applications. We will also return to arrays and discover some of n on ly 295 $data = 454; print gettype( $data ); // prints "integer" You can change variables from one type to another, either by casting or with the before the variable or value you want to convert. By casting a variable, you do not change the contents of a variable in any way. Instead, a converted copy is returned to you. The following code fragment casts a double to an integer: $data = 4.333; print ( integer ) $data; // prints 4 The $data variable still contains the double that we assigned to it. We have merely printed the return value of the cast. To transform the type of a variable, you can use the settype() function. settype() requires the name of a data type and a variable to convert: settype( $data, integer ); print $data; // prints 4 that it transforms one of the arguments you pass it in your scope as well as its own. Converting Complex Types You have already looked in some detail at the process of converting between simple data types (scalars and strings). What happens when you convert between simple data types such as doubles or integers and more complex types such as objects and arrays? No When you cast a simple data type to an array, an array is created, with the original value in the first element: $str = "this is my string"; $arr_str = (array) $str; tf or co m er The $data variable now contains an integer. settype() is a rare function in PHP in cia l, http://i-tronics.blogspot.com/ us e $data = 4.333; fo re du ca tio n on ly settype() function. To cast a function, place the name of a data type in brackets 296 print $arr_str[0]; // prints "this is my string" When you cast a scalar or string variable to an object, an object is created with a single property called scalar. This contains the original value: $arr_str = (object) $str; print $arr_str->scalar; // prints "this is my string" Things get a little more interesting when you convert between arrays and objects. When you convert an array to an object, a new object is created with a property for each key in the array: $addresses = array ( street => "Williams Street", town => "Stockton" ); $obj_addresses = ( object ) $addresses; print $obj_addresses->street; // prints "Williams Street" each object property. Methods are discarded. class Point { var $x; var $y; { No $point = new Point( 5, 7 ); $array_point = (array) $point; print $array_point[x]; // prints 5 http://i-tronics.blogspot.com/ tf or $this->x = $x; $this->y = $y; } } co function Point( $x, $y ) m er cia l, us Conversely, converting an object to an array creates an array with an element for e fo re du ca tio n on ly $str = "this is my string"; 297 Automatic Conversion of Data Types If you build an expression that has values of two different data types as operands, PHP automatically converts one to the type of the other to arrive at a result. You compiled from form input will always be strings, but you might have used them in a test expression or a calculation as if they were numbers. have probably taken advantage of this already without thinking about it. Variables Suppose that you have asked a user to tell the number of hours they spend online a week, storing the input in a variable called $hours. This initially will be stored as a string. $hours = "15"; if ( $hours == 15 ) print "As a frequent user you may qualify for a discount"; In the test for equivalence, the string "15" is cast to an integer, and the test expression resolves to true. or doubles, strings will be converted according to their contents. If a string begins 80: 4 * If a string does not begin with a number, it will be converted to 0. So this line will give 0: 4 * "about 20mb"; If a string contains a number followed by a dot, it will be converted into a double. So No 4 The autoincrement and autodecrement operators are a special case when applied to strings. Incrementing a string adds 1 to the converted value of the string as you would expect, but only if the string contains nothing but numbers. The new value will itself be a string: $str = "4"; tf the following example will give 4.8: * "1.2"; or co m er "20mb"; cia l, with an integer, it will be converted to that number. So the following line will give http://i-tronics.blogspot.com/ us The rules for automatic conversion are relatively simple. In the context of integers e fo re du ca tio n on ly 298 $str++; print $str; // prints 5 print gettype( $str ); // prints "string" If you attempt to autoincrement a string that contains letters, the final character $str = "hello"; $str++; print $str; // prints "hellp" Compare this with another approach to incrementing a string: $str = "hello"; $str += 1; print $str; // prints 1; print gettype( $str ); // prints "integer" In the previous example, $str is converted to the integer 0 when we add 1 to it. The Automatic conversions between integers and doubles are more straightforward. If converted to a double, and the result will be a double: $result = ( 1 + 20.0 ); print gettype ( $result ); // prints "double" It is important to note that when automatic conversions occur for the purposes of operand needs to be converted, it is a transformed copy that will be used as part of No Testing Data Types You've already seen that you can test any data type with the gettype() function. This is useful for debugging because it tells you exactly what type any variable is. Often, though, you will only want to check whether a variable contains a specific type. PHP provides a special function corresponding to each data type. These http://i-tronics.blogspot.com/ tf the expression. or evaluating an expression, neither operand in the expression is itself changed. If an co m er cia l, either operand in an expression is a double, then the other operand will be us e result of this operation, 1, is stored back in $str. $str will now hold an integer. fo re du ca tio n on ly alone will be incremented: 299 functions accept a variable or value and return a boolean. Table 16.1 lists these functions. Table 16.1: Functions to Test Data Types Function is_array() Description Returns true if the argument is an array is_bool() Returns true if the argument is boolean is_double() Returns true if the argument is a double is_int() Returns true if the argument is an integer the argument is is_string() These functions make testing data types a little easier. if ( gettype( $var ) == "array" ) No if ( is_array( $var ) ) print "it's an array"; The second way of testing the $var variable is a little more compact and is nicely intuitive. tf is equivalent to or print "it's an array"; co m er cia l, an object Returns true if the argument is a string http://i-tronics.blogspot.com/ us is_object() Returns true if e fo re du ca tio n on ly 300 More Ways of Changing Type You have already seen two ways of converting data types. You can either cast a value or use the settype() function. In addition to these techniques, PHP provides accept values of any type apart from array or object and return a converted value. Table 16.2 lists these functions. Table 16.2: Functions to Convert Data Types Function doubleval() Description Accepts a value and double functions to convert values into integers, doubles, and strings. These functions equivalent intval() Accepts a value and integer strval() cia l, Why Are Data Types Important? implicitly converts types for you when you use variables of different data types in track of the types of data you are storing? It is often a good idea to keep track of the data that your variables store to prevent errors. Imagine that you are writing a function that prints the keys and values of an array to the browser. PHP is relaxed about arguments to functions, so you can't demand that the calling code pass you an array when you declare your function. function printArray( $array ) No tf expressions. If PHP makes things so easy, why is it important to be able to keep or PHP does not demand that you declare a data type when you create a variable. It co m er http://i-tronics.blogspot.com/ us equivalent Accepts a value and returns string equivalent e fo re du ca returns returns tio n on ly 301 { foreach ( $array as $key => $val ) print "$key: $val<P>"; } argument. printArray( array(4, 4, 55) ); printArray( 4 ); // Warning: Non array argument supplied for foreach() in // /home/matt/htdocs/php-book/data/test2.php on line 5 By testing the data type of the supplied argument, you can make the function more accommodating. You could make the function q uietly return if it receives a scalar value: function printArray( $array ) { if ( ! is_array( $array ) ) return false; foreach ( $array as $key => $val ) print "$key: $val<P>"; return true; } it was able to complete its task. You could even use a cast to convert scalar data into an array: function printArray( $array ) { if ( ! is_array( $array ) ) $array = (array) $array; foreach ( $array as $key => $val ) No tf or The calling code can now test the return value of the function to ascertain whether co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio If you carelessly pass a scalar, you will get an error, as in the following example: n on ly The preceding function will work nicely if the function is called with an array 302 print "$key: $val<P>"; return true; } The printArray() function has become vastly more flexible. It will now output any Checking data types can also be useful when testing the return value of some functions. Some languages, such as Java, always return a predetermined data type to ambiguities. from any method. PHP has no such restriction. This flexibility can occasionally lead returns false when it has reached the end of the directory that you are reading, and a string containing the name of an item in the directory at all other times. Traditionally, you would use a construction similar to $dh = opendir( "mydir" ); while ( $name = readdir( $dh ) ) print "$name<br>"; closedir( $dh ); statement's test expression will evaluate this string to false, ending the listing. By testing the data type of the return value of readdir(), you can circumvent this problem: $dh = opendir( "mydir" ); print "$name<br>"; closedir( $dh ); No Testing for Absence and Emptiness Testing the data type of variables can be useful, but you must first be sure that a variable exists and, if it does exist, that a value has been assigned to it. You can do this with the isset() function. isset() requires a variable and returns true if the variable contains a value: $notset; http://i-tronics.blogspot.com/ tf or co while ( is_string( $name = readdir( $dh ) ) ) m er cia l, to read the items in a directory. If a directory is named 0, however, the while us e fo re du ca You saw an example of this in Hour 10, "Working with Files." The readdir() function tio n on ly data type in an array context, even an object. 303 if ( isset( $notset ) ) print "\$notset is set"; else print "\$notset is not set"; // prints "$notset is not set" A variable that is declared but has not yet been assigned a value will not be recognized as set. a variable, it will be recognized as having been set: $notset = ""; if ( isset( $notset ) ) print "\$notset is set"; else print "\$notset is not set"; // prints "$notset is set" Variables that have been initialized as a result of form submissions will always be set, even if the user did not add any data to a field. To deal with situations like this, you must test whether a variable is empty. empty() accepts a variable and returns true if the variable is not set, or if it contains data other than 0 or an empty string. It also returns true if the variable contains an empty array: $notset = ""; if ( empty( $notset ) ) print "\$notset is empty"; No // prints "$notset is empty" More About Arrays tf or else print "\$notset contains data"; co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio You should be aware of one danger, however. If you assign 0 or an empty string to n on ly 304 In Hour 7, "Arrays," we introduced arrays and some of the functions that you can use to work with them. This section introduces some more functions and techniques. An Alternative Approach to Traversing Arrays PHP4 introduced the foreach statement, a powerful tool for reading array elements. We use this in most of the examples in this book. For scripts written in PHP3, it was source code that was written before the release of PHP4, it is essential that you know about this. When you create an array, PHP maintains an internal pointer that initially points at the first element in the array. You can access this element's key and value with a function called each(). each() requires an array variable and returns a four-element array. Two of these elements will be numerically indexed, and two will be labeled with the names "key" and "value," respectively. After each() has been called, the unless the end of the array has been reached, in which case the function returns false. Let's create an array and try out the each() function: $details = array( school => "Slickly High", course => "Selective Indifference" ); $element = each( $details ); print "$element[0]<BR>"; print "$element[1]<P>"; internal pointer moves on to the next element in the array that you are examining, m er print "$element[value]<BR>"; co print "$element[key]<BR>"; We initialize an array called $details with two elements. We then pass $details to the each() function, storing the return value in a new array called $element. The $element array holds the key and value of the first element of the $details. Assigning the array returned by each() to an array variable is cumbersome. Fortunately, PHP provides the list() function. list() accepts any number of variables and populates each of them with the corresponding values from an array value: $array = array( 44, 55, 66, 77 ); list( $first, $second ) = $array; No tf or cia l, // prints "school" // prints "Slickly High" // prints "school" // prints "Slickly High" http://i-tronics.blogspot.com/ us e fo re du ca tio scripts that should be compatible with PHP3 or are interested in learning from n necessary to use a different technique to traverse arrays. If you intend to distribute on ly 305 print "$first"; print "<BR>"; print "$second"; // prints 55 // prints 44 Notice how we were able to copy the first two elements of the array in the previous We can use the list() function to assign values to two variables every time each() is called. We can then work with these, just as we would in a foreach statement. course => "Selective Indifference" ); while ( list ( $key, $value ) = each( $details ) ) print "$key: $value<BR>"; Although this code will work, a line still is missing. If your array has been traversed before, the internal pointer will still be set beyond the last element. You can set the internal pointer back to the beginning of an array with the reset() function. reset() requires an array variable as its argument. So, the more familiar construction foreach( $details as $key => $value ) print "$key: $value<BR>"; is equivalent to reset( $details ); while ( list ( $key, $value ) = each( $details ) ) print "$key: $value<BR>"; Checking That a Value Exists in an Array No Prior to PHP4, if you needed to check whether a value existed in an array, you had to traverse the array until you had either found a match or reached the last element. PHP4 provides the in_array() function. in_array() requires two arguments, the value for which you are searching and the array you want to search. The function returns true if the value is found with the given array and false otherwise. $details = array( school => "Slickly High", tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n $details = array( school => "Slickly High", on ly example into named variables using the list() function. 306 course => "Selective Indifference" ); if ( in_array( "Selective Indifference", $details ) ) print "This course has been suspending pending investigation<P> \n"; Removing an Element from an Array You can remove any element from an array with the unset() function. unset() requires a variable or an array element as an argument and will unceremoniously destroy it. If the argument is an array element, the array will be automatically shortened. unset( $test[address] ); unset( $numbers[1] ); One potential pitfall with unset() is the fact that array indices are not subsequently changed to reflect the new size of the array. So, having removed $numbers[1] in the previous example, the $numbers array might now look something like this: $numbers[0] $numbers[2] $numbers[3] You can still loop through this with a foreach statement without problems, however. Applying a Function to Every Element in an Array element of an array is a little more difficult. If you want to add a number to the value array updating each element. PHP provides a neater answer, however. The array_walk() function passes the key and value of every element in an array to a user-defined function. array_walk() requires an array variable, a string representing the name of a function, and an optional additional argument that will be passed to the function you have chosen. Let's create an example. We have an array of prices acquired from a database, but before working with it we need to add sales tax to each price. First, we should create the function to add the tax: No tf or of every array element, for example, one solution would be to loop through the co You can change a scalar variable easily in an expression. Applying a change to every m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 307 function add_tax( &$val, $key, $tax_pc ) { $val += ( ($tax_pc/100) } * $val ); key, a value, and, optionally, a further argument. If you want to change the value that is passed to your function, you need to append value will be passed by reference and any changes you make to the value within the return a value. Now that we have created the function, we can call it via array_walk(): function add_tax( &$val, $key, $tax_pc ) { $val += ( ($tax_pc/100) } * $val ); $prices = array( 10, 17.25, 14.30 ); foreach ( $prices as $val ) print "$val<BR>"; // Output: // 11 // 18.975 // 15.73 We pass the $prices array variable to array_walk() along with the name of the No add_tax() function. add_tax() needs to know the current sales tax rate. The so this is where we set the tax rate. optional third argument to array_walk() will be passed to the nominated function, Custom Sorting Arrays You have already seen how to sort arrays by key or value. You do not always want to sort an array in such a straightforward way, however. You may want to sort it tf or co m er cia l, array_walk( $prices, "add_tax", 10 ); http://i-tronics.blogspot.com/ us e fo re du ca function will be reflected in the array. That is why our add_tax() function does not tio n an ampersand to the argument in the function declaration. This ensures that the on ly Any function to be used with array_walk() should expect arguments representing a 308 according to the values of an element buried in a multidimensional array, for example, or to use a criterion completely different to the standard alphanumeric comparison. PHP enables you to define your own comparison functions to sort arrays. To do this for a numerically indexed array, you would call the usort() function, which requires the array you want to sort and the name of the function you want to make the necessary comparisons. The function you define should accept two arguments, which will hold the array values to be compared. If they are equivalent according to your criterion, the subject array, the function should return − 1. If the first argument should come after Listing 16.1 uses usort() to sort a multidimensional array. Fields 1: <?php 2: $products = array( 3: 4: 5: 6: 7: 9: 10: 11: 12: 13: 14: 15: { array( name=>"HAL 2000", array( name=>"Tricorder", array( name=>"ORAC AI", ); Listing 16.1: Using usort() to Sort a Multidimensional Array by One of Its fo re du ca price=>4500.5 price=>55.5 ), price=>2200.5 ) the second, the function should return 1. us e 8: function priceCmp( $a, $b ) if ( $a[price] == $b[price] ) return 0; if ( $a[price] < $b[price] ) return − 1; No 16: usort( $products, priceCmp ); 17: foreach ( $products as $val ) 18: print "$val[name]: $val[price]<BR>\n"; 19: ?> We define an array called $products, which we want to sort by the price field of each tf or return 1; } co m er cia l, array( name=>"Sonic Screwdriver", price=>22.5 http://i-tronics.blogspot.com/ tio ), ), n function should return 0; if the first argument should come before the second in the on ly 309 of its values. We then create the custom sort function, priceCmp(). This function accepts two arguments, $a and $b. These arguments will hold two the arrays that make up the second level of the $products array. We compare their price elements, returning 0 if the prices are the same, − 1 if the first is less than the second, and 1 otherwise. Having defined both function and array, we call the usort() function, passing it the $products array and the name of our comparison function. usort() calls our function the elements according to the return value it receives. repeatedly, passing it elements from the $products array and switching the order of Use usort() for sorting numerically indexed arrays. If you want to apply a similar association between keys and values. Listing 16.2 sorts an associative array using uasort(). One of Its Fields 1: <?php 2: $products = array( 3: 4: 5: 6: 7: 9: 10: 11: 12: 13: 14: 15: if { if Listing 16.2: Using uasort() to Sort a Multdimensional Associative Array by "Tricorder" => array( color =>"blue", us "HAL 2000" => array( color =>"red", e fo re du ca price=>55.5 custom sort to an associative array, use uasort(). uasort() will sort maintaining the price=>4500.5 "Sonic Screwdriver" => array( color =>"red", ); cia l, "ORAC AI" => array( color =>"green", price=>2200.5 tio ), ), ), price=>22.5 n ) Finally, we loop through the array, to demonstrate our new ordering. ( $a[price] == $b[price] ) No 16: uasort( $products, priceCmp ); 17: foreach ( $products as $key => $val ) 18: 19: ?> print "$key: $val[price]<BR>\n"; tf or return 1; } co return 0; return − 1; ( $a[price] < $b[price] ) m er 8: function priceCmp( $a, $b ) http://i-tronics.blogspot.com/ on ly 310 You can custom sort an associative array by its keys using the function uksort(). uksort() is exactly the same in principle as usort() and uasort(), except that uksort() compares the keys of the array. Listing 16.3 uses uksort() to sort an array by the number of characters in each key. Looking ahead to the next hour, we use the function strlen() to ascertain the length in characters of each key. strlen() requires a single string argument and returns an integer representing the number of characters in the string. Its Keys 1: <?php 2: $exes = array( 3: 4: 5: 6: 7: 8: 10: 11: 12: 13: 14: 15: 16: } { return 0; xxxx => 4, xxx => 5, xx => 7, xxxxx => 2, x => 8 ); Listing 16.3: Using uksort() to Sort an Associative Array by the Length of if ( strlen( $a ) == strlen( $b ) ) if ( strlen( $a ) < strlen( $b ) ) return − 1; return 1; 17: uksort( $exes, priceCmp ); 18: foreach ( $exes as $key => $val ) 19: 20: print "$key: $val<BR>\n"; No 22: // x: 8 23: // xx: 7 24: // xxx: 5 25: // xxxx: 4 26: // xxxxx: 2 27: 28: ?> tf 21: // output: or co m er cia l, http://i-tronics.blogspot.com/ us e 9: function priceCmp( $a, $b ) fo re du ca tio n on ly 311 Summary In this hour, you got your hands dirty with some of the more advanced aspects of working with arrays and data types. You learned what happens when you cast different data types in an expression, automatically casting one of them for you. You learned about functions, such as is_array(), that test for specific data types, and functions, such as intval(), that convert data to a specific type. You learned about complex data types to scalars and vice versa. You learned how PHP deals with how to check that a value exists in an array with in_array() and how to remove an element from an array with unset(). You learned how to transform an array with array_walk(). Finally, you learned about the custom sort functions with usort(), uasort(), and uksort(). Q&A A No, there are even more array functions than we have space to cover in this book! http://www.php.net/manual/ref.array.php. Workshop material covered. Try to understand the quiz answers before continuing to the next Quiz No print "four" tf What single function could you use to convert any data type to any other data type? Could you achieve the same thing without a function? What will the following code print? * How would you determine whether a variable contains an array? or hour's lesson. Quiz answers are provided in Appendix A. co The Workshop provides quiz questions to help you solidify your understanding of the 200; m er cia l, You can see them us e Q Have we now covered every array function that PHP4 provides? all fo re du ca listed and tio the traditional way of traversing an array in PHP using each() and list(). You learned n described http://i-tronics.blogspot.com/ on ly at 312 Which function is designed to return the integer value of its argument? How would you test whether a variable has been set? How would you test whether a variable contains an empty value, such as 0 or an empty string? What function would you use to delete an array element? What function could you use to custom sort a numerically indexed array? Activities book. Convert any that use the foreach statement so that they are compatible Create an array of mixed data types. Custom sort the array by data type. No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca with PHP3. tio n Look back through some of the scripts you have created whilst working with this on ly 313 Hour 17: Working with Strings Overview The World Wide Web is very much a plain text environment. No matter how rich Web content becomes, HTML lies behind it all. It is no accident, then, that PHP4 provides many functions with which you can format, investigate, and manipulate strings. In this hour, you will learn How to format strings How to find a substring within a string How to determine the length of a string How to break a string down into component parts How to replace substrings How to change the case of a string How to remove white space from the beginning or end of a string Formatting Strings Until now, we have simply printed any strings that we want to display directly to the browser. PHP provides two functions that allow you first to apply formatting, within a field, or display data according to different number systems. In this section, you will look at a few of the formatting options provided by printf() and sprintf(). Working with printf() whether to round doubles to a given number of decimal places, define alignment No PHP version is similar but not identical. printf() requires a string argument, known as a format control string. It also accepts additional arguments of different types. The format control string contains instructions as to how to display these additional arguments. The following fragment, for example, uses printf() to output an integer as a decimal: printf("This is my number: %d", 55 ); // prints "This is my number: 55" tf If you have any experience with C, you will be familiar with the printf() function. The or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 314 Within the format control string (the first argument), we have included a special code, known as a conversion specification. NEW TERM A conversion specification begins with a percent (%) symbol and defines how to treat the corresponding argument to printf(). You can include as many conversion specifications as you want within the format control string, as long as you send an equivalent number of arguments to printf(). The following fragment outputs two numbers using printf(): // Output: // First number: 55 // Second number: 66 The first conversion specification corresponds to the first of the additional arguments to printf(), which is 55. The second conversion specification corresponds to 66. The d following the percent symbol requires that the data be treated as a decimal integer. This part of a conversion specification is a type specifier. You have already come across one type specifier d, which displays data in decimal format. Table 17.1 lists the other type specifiers that are available. Table 17.1: Type Specifiers Specifier d m er cia l, us printf() and Type Specifiers e co or tf No b fo re du ca Display a number Display binary number Display integer Description argument as decimal integer as a c http://i-tronics.blogspot.com/ tio an an as n printf("First number: %d<br>\nSecond number: %d<br>\n", 55, 66 ); on ly 315 ASCII equivalent f Display an integer as a floating-poin (double) o Display integer an t number an s x fo re du ca (base 8) Display a string Display number argument as e integer as a lowercase hexadecimal number (base 16) Display integer an uppercase hexadecimal number (base 16) an as X No Listing 17.1 uses printf() to display a single number according to some of the type specifiers listed in Table 17.1. Notice that we do not only add conversion specifications to the format control string. Any additional text we include will be printed. Listing 17.1: Demonstrating Some Type Specifiers tf 1: <html> http://i-tronics.blogspot.com/ or co m er cia l, us tio octal an n as on ly 316 2: <head> 3: <title>Demonstrating some type specifiers</title> 4: </head> 5: <body> 6: <?php 7: $number = 543; 8: printf("Decimal: %d<br>", $number ); 9: printf("Binary: %b<br>", $number ); 10: printf("Double: %f<br>", $number ); 11: printf("Octal: %o<br>", $number ); 12: printf("String: %s<br>", $number ); 13: printf("Hex (lower): %x<br>", $number ); 14: printf("Hex (upper): %X<br>", $number ); 15: ?> 16: </body> 17: </html> Figure 17.1 shows the output for Listing 17.1. As you can see, printf() is a quick way No Figure 17.1: Demonstrating conversion specifiers. tf or co m er of converting data from one number system to another and outputting the result. cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly 317 When you specify a color in HTML, you combine three hexadecimal numbers between 00 and FF, representing the values for red, green, and blue. You can use printf() to convert three decimal numbers between 0 and 255 to their hexadecimal equivalents: $red = 204; $blue = 204; printf( "#%X%X%X", $red, $green, $blue ); // prints "#CCCCCC" numbers, you can't use it to determine how many characters the output for each argument should occupy. Within an HTML color code, each hexadecimal number should be padded to two characters, which would become a problem if we changed our $red, $green, and $blue variables in the previous fragment to contain 1, for example. We would end up with the output "#111". You can force the output of leading zeroes by using a padding specifier. You can require that output be padded by leading characters. The padding specifier should directly follow the percent sign that begins a conversion specific ation. To pad by the number of characters you want the output to take up. If the output occupies fewer characters than this total, the difference will be filled with zeroes: printf( "%04d", 36 ); // prints "0036" output with leading zeroes, the padding specifier should consist of a zero followed character followed by the number of characters that the output should occupy: No printf( "% 4d", 36 ) // prints " 36" Note A browser will not display multiple spaces in an HTML document. You can force the display of spaces and newlines by placing <PRE> tags around your output. <pre> tf To pad output with leading spaces, the padding specifier should consist of a space or co m er cia l, http://i-tronics.blogspot.com/ us Padding Output with the Padding Specifier e fo re du ca Although you can use the type specifier to convert from decimal to hexadecimal tio n on ly $green = 204; 318 <?php print "The ?> </pre> spaces will be visible"; header() function to change the Content-Type header. header("Content-Type: Text/Plain"); browser for the header() function to work as desired. You can specify any character other than a space or a zero in your padding specifier with a single quotation mark followed by the character you want to use: printf ( "%'x4d", 36 ); // prints "xx36" We now have the tools we need to complete our HTML code example. Until now, we $red = 1; $green = 1; $blue = 1; printf( "#%02X%02X%02X", $red, $green, $blue ); // prints "#010101" two spaces, leading zeroes will be added. Specifying a Field Width No You can specify the number of spaces within which your output should sit. The field width specifier is an integer that should be placed after the percent sign that begins a conversion specification (assuming that no padding specifier is defined). The following fragment outputs a list of four items, all of which sit within a field of 20 spaces. To make the spaces visible on the browser, we place all our output within a PRE element. tf or co Each variable is output as a hexadecimal number. If the output occupies fewer than m er cia l, http://i-tronics.blogspot.com/ us e could convert three numbers, but we could not pad them with leading zeroes: fo re du ca tio Remember that your script must not have sent any output to the n on ly If you wish to format an entire document as text, you can use the 319 print "<pre>"; printf("%20s\n", "Books"); printf("%20s\n", "CDs"); printf("%20s\n", "Games"); printf("%20s\n", "Magazines"); print "</pre>"; Figure 17.2 shows the output of this fragment. By default, output is right-aligned within the field you specify. You can make it left-aligned by prepending a minus (− ) symbol to the field width specifier: printf("%− 20s\n", "Left aligned"); Note that alignment applies to the decimal portion of any number that you output. In other words, only the portion before the decimal point of a double will sit flush to the end of the field width when right aligned. Specifying Precision No If you want to output data in floating-point format, you can specify the precision to which you want to round your data. This is particularly useful when dealing with currency. The precision identifier should be placed directly before the type specifier. It consists of a dot followed by the number of decimal places to which you want to round. This specifier only has an effect on data that is output with the f type specifier: printf( "%.2f", 5.333333 ); tf or co m er cia l, http://i-tronics.blogspot.com/ us Figure 17.2: Aligning with field width specifiers. e fo re du ca tio n on ly 320 // prints "5.33" Note In the C language, it is possible to use a precision specifier with printf() to specify padding for decimal output. The precision specifier will have no effect on decimal output in PHP4. Use the padding specifier to add leading zeroes to integers. Conversion Specifications: A Recap specifier and a field width specifier. You should choose to use one or the other, but not both. Table 17.2: Components of Conversion Specification Name Padding specifier fo re du ca of characters should occupy, and to characters otherwise the which output should within formatted places Description Determines the number us e that output cia l, m er co Field width specifier Determines space No tf or Precision specifier Determines the number of decimal to http://i-tronics.blogspot.com/ tio the add be order that they would be included. Note that it is difficult to use both a padding n Table 17.2 lists the specifiers that can make up a conversion specification in the on ly Example ' 4' '20' '.4' 321 which double should rounded Type specifier Determines the type should output Listing 17.2 uses printf() to output a list of products and prices. data that be 'd' be a 1: <html> 2: <head> 3: <title>Using printf() to format a list of product prices</title> 4: </head> 5: <body> 6: <?php 7: $products = Array( 8: 9: 10: "Candlestick"=>"4", 12: printf("%− 20s%23s\n", "Name", "Price"); No 15: 16: printf("</pre>"); 17: ?> 18: </body> 19: </html> tf 14: foreach ( $products as $key=>$val ) printf( "%− 20s%20.2f\n", $key, $val ); or 13: printf("%'− 43s\n", ""); co 11: print "<pre>"; m er "Coffee table"=>80.6 ); cia l, "Green armchair"=>"222.4", http://i-tronics.blogspot.com/ us e fo re du ca Listing 17.2: Using printf() to Format a List of Product Prices tio n on ly 322 We first define an associative array containing product names and prices. We print a PRE element, so that the browser will recognize our spaces and newlines. Our first printf() call defines the following format control string: "%− 20s%23s\n" The first conversion specification ("%− 20s") uses a field width specifier of 20 conversion specification ("%23s") sets up a right-aligned field width. This printf() characters, with the output left-justified. We use a string type specifier. The second call will output our field headers. characters. We achieve this with a padding specifier, which adds padding to an empty string. The final printf() call is part of a foreach statement that loops through our product array. We use two conversion specifications. The first ("%− 20s") prints the product name as a string left-justified within a 20-character field. The second conversion specification ("%20.2f") uses a field width specifier to ensure that output will be double we output is rounded to two decimal places. right-aligned within a 20-character field, and a precision specifier to ensure that the Storing a Formatted String printf() outputs data to the browser, which means that the results are not available to your scripts. You can, however, use the functionsprintf(), which works in exactly the same way as printf() except that it returns a string that you can then store in a variable for later use. The following fragment uses sprintf() to round a double to two decimal places, storing the result in $dosh: No $dosh = sprintf("%.2f", 2.334454); print "You have $dosh dollars to spend"; tf or co m er cia l, Figure 17.3 shows the output of Listing 17.2. http://i-tronics.blogspot.com/ us e fo re du ca Our second printf() function call draws a line of − characters across a field of 43 tio n on ly 323 Figure 17.3: Products and prices formatted with printf(). A particular use of sprintf() is to write formatted data to a file. You can call sprintf() and assign its return value to a variable that can then be printed to a file with fputs(). Investigating Strings Web pages. Before you begin to work with data from an external source, you often acquire information about strings. A Note About Indexing Strings across the word more frequently in the context of arrays. In fact, strings and arrays characters. So you can access individual characters of a string as if they were elements of an array: No $test = "scallywag"; print $test[0]; // prints "s" print $test[2]; // prints "a" tf or are not as different as you might imagine. You can think of a string as an array of co We will frequently use the word index in relation to strings. You will have come m er cia l, will need to find out more about it. PHP4 provides many functions that enable you to http://i-tronics.blogspot.com/ us Strings can arrive from many sources, including user input, databases, files, and e You do not always know everything about the data that you are working with. fo re du ca tio n on ly 324 It is important to remember, therefore, that when we talk about the position or index of a character within a string, characters, like array elements, are indexed from 0. Finding the Length of a String with strlen() You can use strlen() to determine the length of a string. strlen() requires a string and returns an integer representing the number of characters in the variable you print "Thank you!"; else print "Your membership number must have 4 digits<P>"; The user is thanked for his input only if the global variable $membership contains four characters; otherwise, an error message is generated. You can use strstr() to test whether a string exists embedded within another string. strstr() requires two arguments: a source string and the substring you want to find the portion of the source string beginning with the substring. For the following example, imagine that we want to treat membership codes that contain the string AB differently from those that do not: $membership = "pAB7"; if ( strstr( $membership, "AB" ) ) within it. The function returns false if the substring is absent. Otherwise, it returns No else Because our test variable $membership does contain the string AB, strstr() returns the string AB7. This resolves to true when tested, so we print a special message. What happens if our user enters "pab7"? strstr() is case sensitive, so AB will not be found. The if statement's test will fail, and the default message will be printed to the http://i-tronics.blogspot.com/ tf print "Thank you. Don't forget that your membership expires soon!"; print "Thank you!"; or co m er cia l, us Finding a Substring Within a String with strstr() e fo re du ca if ( strlen( $membership ) == 4 ) tio The following fragment tests a membership code to ensure that it is four digits long: n have passed it. strlen() might typically be used to check the length of user input. on ly 325 browser. If we want search for either AB or ab within the string, we must use stristr(), which works in exactly the same way but is not case sensitive. Finding the Position of a Substring with strpos() to be found. strpos() requires two arguments: the source string and the substring you are seeking. The function also accepts an optional third argument, an integer substring begins. The following fragment uses strpos() to ensure that a string begins with the string mz: $membership = "mz00xyz"; if ( strpos($membership, "mz") === 0 ) print "hello mz"; Notice the trick we had to play to get expected results. strpos() finds mz in our zero, which will resolve to false in our test. To work around this, we use PHP4's new equivalence operator ===, which returns true if the left- and right-hand operands are equivalent and of the same type. Extracting Part of a String with substr() substr() returns a portion of a string based on the start index and length of the the starting index. It returns all characters from the starting index to the end of the be an integer representing the length of the string you want returned. If this argument is present, substr() returns only the number of characters specified from No the start index onwards. $test = "scallywag"; print substr($test,6); // prints "wag" print substr($test,6,2) // prints "wa" tf or string you are searching. substr() optionally accepts a third argument, which should co portion you are looking for. strstr() demands two arguments, a source string, and m er cia l, http://i-tronics.blogspot.com/ us e string, but it finds it at the first element of the string. This means that it will return fo re du ca tio not exist, strpos() returns false; otherwise, it returns the index at which the n representing the index from which you want to start searching. If the substring does on ly strpos() tells you both whether a string exists within a larger string and where it is 326 If you pass substr() a minus number as its second (starting index) argument, it will count from the end rather than the beginning of the string. The following fragment writes a specific message to people who have submitted an email address ending in .uk. $test = "matt@corrosive.co.uk"; print "Don't forget our special offers for British customers"; else print "Welcome to our shop!"; Tokenizing a String with strtok() You can parse a string word by word using strtok(). strtok() initially requires two arguments, the string to be tokenized and the delimiters by which to split the string. The delimiter string can include as many characters as you want. strtok() will return the first token found . After strtok() has been called for the first time, the source delimiter string. The function will return the next found token every time it is called, returning false when the end of the string is reached. strtok() will usually be called host and path from the query string, and further dividing the name/value pairs of the query string. Figure 17.3 shows the output from Listing 17.3. Listing 17.3: Dividing a String into Tokens with strtok() repeatedly within a loop. Listing 17.3 uses strtok() to tokenize a URL, splitting the string will be cached. For subsequent calls, you should only pass strtok() the 2: <head> No 10: $delims = "?&"; tf 4: 5: </head> 6: <body> 7: <?php 8: $test = "http://www.deja.com/qs.xp? 9: OP=dnquery.xp&ST=MS&DBS=2&QRY=developer+php"; or 3: <title>Listing 17.3 Dividing a string into tokens with strtok()</title> co 1: <html> m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly if ( $test = substr( $test, − 3 ) == ".uk" ) 327 11: $word = strtok( $test, $delims ); 12: while ( is_string( $word ) ) 13: 14: 15: 16: 17: 18: ?> 19: </body> 20: </html> { if ( $word ) print "$word<br>"; $word = strtok( $delims); } strtok() is something of a blunt instrument, and a few tricks are required to work with it. We first store the delimiters that we want to work with in a variable, $delims. We call strtok(), passing it the URL we want to tokenize and the $delims string. We we test that $word is a string. If it isn't, we know that end of the string has been reached and no further action is required. store the first result in $word. Within the conditional expression of the while loop, We are testing the return type because a string containing two delimiters in a row would cause strtok() to return an empty string when it reaches the first of these delimiters. So a more conventional test such as while ( $word ) { $word = strtok( $delims ); would fail if $word is an empty string, even if the end of the source string has not yet No been reached. Having established that $word contains a string, we can go on to work with it. If $word does not contain an empty string, we print it to the browser. We must then call strtok() again to repopulate the $word variable for the next test. Notice that we don't pass the source string to strtok() a second time. If we were to do this, the first word of the source string would be returned once again, and we would find ourselves in an infinite loop. http://i-tronics.blogspot.com/ tf or } co m er cia l, us e fo re du ca tio n on ly 328 Manipulating Strings PHP4 provides many functions that will transform a string argument, subtly or radically. Cleaning Up a String with trim() and ltrim() When you acquire text from the user or a file, you can't always be sure that you haven't also picked up white space at the beginning and end of your data. trim() the start and end of a string. It accepts the string to be modified, returning the cleaned-up version. $text = "\t\t\tlots of room to breath $text = trim( $text ); print $text; // prints "lots of room to breath"; shaves any white space characters, including newlines, tabs, and spaces, from both Of course this might be more work than you require. You might want to keep white chop() function exactly the same as you would trim(). Only white space at the end of the string argument will be removed, however: $text = chop( $text ); // prints " co print $test; PHP provides the Itrim() function to strip white space only from the beginning of a string. Once again, this is called with the string you want to transform and returns No a new string, shorn of tabs, newlines, and spaces: "; $text = "\t\t\tlots of room to breath $text = ltrim( $text ); print $test; // prints "lots of room to breath "; tf or m er $text = "\t\t\tlots of room to breath cia l, space at the beginning of a string but remove it from the end. You can use PHP's lots of room to breath"; http://i-tronics.blogspot.com/ us e fo re du ca "; "; tio n on ly 329 Replacing a Portion of a String using substr_replace() substr_replace() works similarly to substr() except that it allows you replace the portion of a string that you extract. The function requires three arguments: the It also accepts an optional length argument. substr_replace() finds the portion of a string specified by the starting index and length arguments, replacing this portion transformed string. with the string provided in the replace string argument and returning the entire string you are transforming, the text you want to add to it, and the starting index. change its second two characters: <? $membership = "mz99xyz"; $membership = substr_replace( $membership, "00", 2, 2 ); print "New membership number: $membership<p>"; // prints "New membership number: mz00xyz" ?> Replacing Substrings Using str_replace str_replace() replaces all instances of a string within another string. It requires three arguments: a search string, the replacement string, and the string on which The following example uses str_replace() to change all references to 1999 to 2000 this transformation is to be effected. The function returns the transformed string. within a string: No $string .= "The 1999 Guide to All Things Good in Europe"; print str_replace("1999","2000",$string); Converting Case PHP provides several functions that allow you to convert the case of a string. When you write user-submitted data to a file or database, you may want to convert it all http://i-tronics.blogspot.com/ tf $string = "Site contents copyright 1999. "; or co m er cia l, us e fo re du ca In the following code fragment, to renew a user's membership code, we must tio n on ly 330 to upper- or lowercase text first, to make it easy to compare later on. To get an uppercase version of a string, use the function strtoupper(). This function requires only the string that you want to convert and returns the converted string: $membership = "mz00xyz"; $membership = strtoupper( $membership ); print "$membership<P>"; // prints "MZ00XYZ" To convert a string to lowercase characters, use the function strtolower(). Once if ( ! ( strpos ( $home_url, "http://" ) === 0 ) ) $home_url = "http://$home_url"; print $home_url; // prints "http://80-www.corrosive.co.uk.proxy.lib.uiowa.edu" PHP also provides a case function that has a useful cosmetic purpose. ucwords() makes the first letter of every word in a string uppercase. In the following fragment, we make the first letter of every word in a user-submitted string uppercase: $full_name = "violet elizabeth bott"; print $full_name; // prints "Violet Elizabeth Bott" touch any other letters. So if the user had had problems with her shift key in the previous example and submitted VIolEt eLIZaBeTH bOTt, our approach would not BOTt, which isn't much of an improvement. We can deal with this by making the No $full_name = ucwords( strtolower($full_name) ); print $full_name; // prints "Violet Elizabeth Bott" tf $full_name = "VIolEt eLIZaBeTH bOTt"; or submitted string lowercase with strtolower() before invoking ucwords(): co have done much to fix the string. We would have ended up with VIolEt ELIZaBeTH m er Although this function makes the first letter of each word uppercase, it does not cia l, $full_name = ucwords( $full_name ); http://i-tronics.blogspot.com/ us e fo re du ca $home_url = strtolower( $home_url ); tio $home_url = "WWW.CORROSIVE.CO.UK"; n again, this requires the string you want to convert and returns a converted version: on ly 331 Breaking Strings into Arrays with explode() The delightfully named explode() function is similar in some ways to strtok(). explode(), though, will break up a string into an array, which you can then store, string that you want to use to break up the source string and the source string itself. The delimiter string can include more than one character, all of which will form a which will be a delimiter in its own right). sort, or examine as you want. explode() requires two arguments: the delimiter $start_date = "2000-01-12"; $date_array = explode("-", $start_date); // $date[0] == "2000" // $date[1] == "01" // $date[2] == "12" Summary Strings are PHP's principal means of communication with the outside world and of storing information for later use. In this hour, you have covered some of the You learned how to format strings with printf() and sprint(). You should be able to learned about functions that investigate strings. You should be able to discover the or extract a substring with substr(). You should be able to tokenize a string with strtok(). No Finally, you learned about functions that transform strings. You can now remove white space from the beginning or end of a string with trim(), ltrim(), or chop(). You can change case with strtoupper(), strtolower(), or ucwords(). You can replace all instances of a string with str_replace(). tf or length of a string with strlen(), determine the presence of a substring with strpos(), co use these functions both to create strings that transform data and lay it out. You m er functions that enable you to take control of the strings in your scripts. cia l, http://i-tronics.blogspot.com/ us e fo re du ca The following fragment breaks up a date and stores the result in an array: tio n single delimiter (unlike multiple delimiter characters passed to strtok(), each of on ly 332 Believe it or not, you are not finished with strings yet. PHP supports regular expressions that are an even more powerful means of working with strings than the functions already examined. Regular expressions are the subject of the next hour. Q&A Q Are there any other string functions that might be useful to me? A Yes. PHP4 has about 60 string functions! You can read about them all in the PHP4 online manual at http://www.php.net/manual/ref.strings.php. Q In the example that demonstrated printf(), we showed the formatting by formatted plain text on a browser? context. If you want to output an entire text document to the browser, however, it is neater to tell the browser to format the entire output as plain text. You can do this with the header() function: The Workshop provides quiz questions to help you solidify your understanding of the material covered. Try to understand the quiz answers before continuing to the next hour's lesson. Quiz answers are provided in Appendix A. Quiz What conversion specifier would you use with printf() to format an integer as a How would you pad the conversion you effected in question 1 with zeroes so that How would you specify a precision of two decimal places for the floating-point number we have been formatting in the previous questions? What function would you use to determine the length of a string? What function would you use to acquire the starting index of a substring within a string? What function would you use to extract a substring from a string? How might you remove white space from the beginning of a string? How would you convert a string to uppercase characters? How would you break up a delimited string into an array of substrings? No tf or the part before the decimal point is four characters long? co double? Write down the full syntax required to convert the integer 33. m er cia l, http://i-tronics.blogspot.com/ us e Workshop fo re du ca A <PRE> tags can be useful if you want to preserve plain text formatting in an HTML tio n wrapping our output in <PRE> tags. Is this the best way of showing on ly 333 Activities Create a feedback form that accepts a user's full name and an email address. Use case conversion functions to capitalize the first letter of each name the user submits and print the result back to the browser. Check that the user's email address contains the @ symbol and print a warning otherwise. Create an array of doubles and integers. Loop through the array converting each element to a floating-point number with a precision of 2. Right-align the output No tf or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n within a field of 20 characters. on ly 334 Hour 18: Working with Regular Expressions Overview Regular expressions are a powerful way of examining and modifying text. They precisely. Be warned that because they are more powerful, they are also slower You should use string functions, therefore, if you don't need the extra power afforded by the use of a regular expression function. PHP supports two flavors of regular expression. It has a set of functions that emulate regular expressions as employed in Perl, and a set of function that support the more limited POSIX regular expressions. You will examine both. In this hour, you will learn How to match patterns in strings using regular expressions The basics of regular expression syntax How to replace text in strings using regular expressions How to work with powerful Perl compatible regular expressions to match and replace patterns in text POSIX Regular Expression Functions POSIX regular expression functions make it possible for you to match and replace expression functions, but we refer to them as POSIX regular expression functions to distinguish them from the similar but more powerful Per1 compatible regular expressions, and because they follow the POSIX definition for extended regular expressions. A regular expression is a combination of symbols that match a pattern in text. Learning how to use regular expressions, therefore, is much more than learning the No tf complex patterns in strings. They are commonly known simply as regular or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca than the more basic string function examined in Hour 17, "Working with Strings." tio enable you to search for patterns within a string, extracting matches flexibly and n on ly 335 arguments and return types of PHP's regular expression functions. We will begin with the functions and use them to introduce regular expression syntax. Using ereg() to Match Patterns in Strings searched, and an array variable into which the results of the search will be placed. ereg() returns an integer representing the number of characters matched if the string "Aardvark advocacy" for the letters "aa." print ereg("aa","aardvark advocacy",$array); print "<br>$array[0]<br>"; // output: // 2 // aa pattern was discovered in the source string, or false otherwise. Let's search the The letters "aa" exist in "aardvark," so ereg() returns 2, which is the number of letters it matched. The first element of the $array variable is also filled with the matched string, which we print to the browser. This might seem strange given that we already know the pattern we are looking for is "aa". We are not, however, limited to looking for predefined characters. We can use a single dot (.) to match any character: print "<br>$array[0]<br>"; // 2 // dv d. matches "d" followed by any character. We don't know in advance what the No second character will be, so the value in $array[0] becomes useful. Using Quantifiers to Match a Character More Than Once When you search for a character in a string, you can use a quantifier to determine the number of times this character should repeat for a match to be made. The tf or co // output: m er print ereg("aa","aardvark advocacy",$array); cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly ereg() requires a string representing a pattern, a string representing the text to be 336 pattern a+, for example, will match at least one "a" followed by "a" zero or more times. Let's put this to the test: if ( ereg("a+","aaaa", $array) ) print $array[0]; // prints "aaaa"; Notice that this regular expression greedily matches as many characters as it can. Table 18.1 lists the quantifiers you can use to test for a recurring character. Table 18.1: Quantifiers for Matching a Recurring Character Does Not Symbol * Description Zero or more instance Example a* ? Zero or one instance a? us instances e + One or more a+ {n} {n,} n instances At least cia l, a{3} instances or co {,n} Up m er n a{3,} to n a{,2} instances At least n1 instances, no more than n2 instances a{1,2} xaax xaaa {n1,n2} No The numbers between braces in Table 18.1 are called bounds. Bounds let you pinpoint exactly the number of times a character should repeat to be matched. NEW TERM Bounds define the number of times a character or range of characters should be matched in a regular expression. You should place your upper and lower bounds between braces after the tf http://i-tronics.blogspot.com/ fo re du ca Matches Match xxxx (Will match ) anything xaax xxxx xaxx xaax xaaa aaaa aaaa aaxx xaax aaax tio n on ly 337 character you wish to match. For example, a{4,5} will match no fewer than 4 and no more than 5 instances of the character a. valid code can be between one and four instances of the letter "y" followed by any number of alphanumeric characters, followed by the number 99. We have been possible. requested by the club to parse a backlog, pulling out the membership codes where $test = "the code is yyXGDH99 -- have you received my sub?"; if ( ereg( "y{1,4}.*99 ", $test, $array ) ) print "Found membership: $array[0]"; // prints "Found membership: yyXGDH99 " In the previous code fragment, the membership code begins with two y characters, followed by four uppercase letters, followed by 99. y{1,4} matches the two y number of characters of any type. characters, and the four uppercase letters are matched by .*, which will match any that the matched pattern ends at 99, we have required a space as the last character. This is returned when we match. Worse than this, if the string we were testing was the previous regular expression would match "y code is yyXGDH99 did you get my 1999" matched any number of characters until it reached 99 followed by a space. Regular expressions are greedy; in other words, they match as many characters as they can. No For this reason, we match all characters until the 99 of 1999 is reached, rather than the final 99 in our membership code. We might go some way towards fixing this if only we could make sure that the characters that we m atch between y and 99 are truly alphanumeric and contain no spaces. In fact, we can do this easily with a character class. tf or So what went wrong? The regular expression matched the y in my, and then co m er "my code is yyXGDH99 did you get my 1999 sub?" cia l, So that would seem to do the job. In fact, we have a long way to go yet. To ensure http://i-tronics.blogspot.com/ us e fo re du ca tio n on ly Let's create an example. A club has allocated membership codes to its members. A 338 Matching Ranges of Characters with Character Classes Until now we have either matched specified characters or used . to match any character. Character classes enable you to match any one of a group of characters. square brackets. [ab] will match "a" or "b." After you have defined a character class, "ababab." To define a character class, you surround the characters you want to match in you can treat it as if it were a character. So [ab]+ will match "aaa," "bbb," or You can also match ranges of characters with a character class: [a– z] will match any number. You can combine ranges and individual characters into one character class, so [a– z5] will match any lowercase letter or the number "5". You can also negate a character class by including a caret (^) character after the opening square bracket: [^A– Z] will match anything apart from an uppercase character. between one and four times, any alphanumeric character any number of times, and the characters "99." $test = "my code is yyXGDH99 did you get my 1999 sub?"; if ( ereg( "y{1,4}[a-zA-Z0-9]*99 ", $test, $array ) ) print "Found membership: $array[0]"; // prints "Found membership: yyXGDH99 " We're getting closer. The character class that we have added will no longer match spaces, so the membership code is now returned. If we add a comma after the membership code in our test string, however, the regular expression fails again: $test = "my code is yyXGDH99, did you get my 1999 sub?"; No if ( ereg( "y{1,4}[a-zA-Z0-9]*99 ", $test, $array ) ) print "Found membership: $array[0]"; // regular expression fails This is because we have demanded a space at the end of the pattern to ensure that we are at the end of the membership code. So if a text includes a membership code in brackets, or before a hyphen or comma, the match will fail. We can amend our tf or co m er cia l, http://i-tronics.blogspot.com/ us e Let's return to the example from the previous section. We need to match "y" fo re du ca lowercase letter, [A– Z] will match any uppercase letter, and [0– 9] will match any tio n on ly 339 regular expression, so that we match anything other than an alphanumeric character, which will get us some way towards a solution: $test = "my code is yyXGDH99, did you get my 1999 sub?"; if ( ereg( "y{1,4}[a-zA-Z0-9]*99[^a-zA-Z0-9]", $test, $array ) ) print "Found membership: $array[0]"; // prints "Found membership: yyXGDH99," We're closer still, but there are still two problems. First, we have included the code is at the end of the string we are testing because it requires a character to exist after the membership code. We need, in other words, to find a reliable way of testing for a word boundary. We will return to this problem. Working with Atoms NEW TERM An atom is a pattern enclosed in brackets (often referred to as a subpattern). After you have defined an atom, you can treat it as if it were itself a character or character class. In other words, you syntax described in Table 18.1. can match the same pattern as many times as you want using the the atom should match twice for the regular expression to succeed: if ( ereg( "([ab]+x){2}", $test, $array ) ) print "$array[0]"; // prints "abbaxabbax" [ab]+x will match "abbax", but ([ab]+x)2 will match "abbaxabbax". The first element of the array variable that is passed to ereg() will contain the No complete matched string. Subsequent elements will contain each individual atom matched. This means that you can access the component parts of a matched pattern as well as the entire match. In the following code fragment, we match an IP address and access not only the entire address, but also each of its component parts: $test = "158.152.55.35"; tf or co m er $test = "abbaxabbaxabbax"; cia l, In the next fragment, we define a pattern, enclose it in brackets, and require that http://i-tronics.blogspot.com/ us e fo re du ca tio n comma in our returned match, and second, the match will fail if the membership on ly 340 if ( ereg( "([0– 9]+)\.([0– 9]+)\.([0– 9]+)\.([0– 9]+)", $test, $array ) ) { foreach ( $array as $val ) print "$val<BR>"; } // Output: // 158.152.1.58 // 158 // 152 // 1 // 58 Notice that we have used a backslash (\) to escape the dots in the regular expression. By doing this, we signal that we want to strip . of its special meaning and treat it as a specific character. You must do the same for any character that has a function in a regular expression if you want to refer to it. You can combine patterns with the pipe ( |) character to create branches in your regular expressions. A regular expression with two branches will match either the expression syntax. In the next code fragment, we match either .com or .co.uk in a string: first pattern or the second. This adds yet another layer of flexibility to regular $test = "www.adomain.com"; No // prints "it is .com domain" Anchoring a Regular Expression Not only can you determine the pattern you want to find in a string, you also can decide where in the string you want to find it. To test whether a pattern is at the tf print "it is a $array[0] domain<BR>"; or if ( ereg( "\.com|\.co\.uk", $test, $array ) ) co m er cia l, http://i-tronics.blogspot.com/ us Branches e fo re du ca tio n on ly 341 beginning of a string, prepend a caret (^) symbol to your regular expression. ^a will match "apple", but not "banana". To test that a pattern is at the end of a string, append a dollar ($) symbol to the end of your regular expression. a$ will match "flea" but not "dear". The Membership Code Example Revisited We now have the tools to complete our membership code examples. Remember that we are parsing emails to extract membership codes that consist of between one and four instances of the letter "y" followed by any number of any alphanumeric pattern is on a word boundary. We can't use a space because a word can be bounded by punctuation. We can't require that a nonalphanumeric character bound the match because our pattern could begin or end a string. Now that we can create branches and anchor patterns, we can require that the membership code be followed either by a nonalphanumeric character or the end of beginning of the code. We can also use brackets to recover the membership code shorn of any punctuation or spaces as follows: the string. We can use the same logic to determine a word boundary at the if ( ereg( "(^|[^a-zA-Z0-9])(y{1,4}[a-zA-Z0-9]*99)([^a-zA-Z0-9]$verbar;$)", $test, $array ) ) print "Found membership: $array[2]"; // prints "Found membership: yyXGDH99" easily. We have ensured that our matched pattern is on a word boundary (as we No define it for these purposes). This means that it must either be preceded by a nonalphanumeric character or the beginning of the string. It must be also be followed by a nonalphanumeric character or the end of the string. We don't want to record any preceding or following characters, so we wrap the pattern we want to extract in brackets. We can then be sure to access it in the second element of the $array array. Note ereg() is case sensitive. If you don't want to match case, you can use tf them down into smaller chunks, however, they usually reveal their secrets quite or As you can see, regular expressions are daunting at first glance. After you break co m er cia l, $test = "my code is yyXGDH99, did you get my 1999 sub?"; http://i-tronics.blogspot.com/ us e fo re du ca characters followed by "99". Our current problem is to determine when a matched tio n on ly 342 eregi(), which is not case sensitive but is the same as ereg() in all other respects. Using egrep_replace() to Replace Patterns in Strings untouched. egrep_replace() enables you to find a pattern in a string and replace it with a new substring. egrep_replace() requires three strings: a regular expression, an unchanged copy of the original source string, otherwise. In the following fragment, we search for the name of a club official, replacing it with name of her successor: $test = "Our Secretary, Sarah Williams is pleased to welcome you."; print ereg_replace("Sarah Williams", "Rev. P.W. Goodchild", $test); // prints "Our Secretary, Rev. P.W. Goodchild is pleased to welcome you." replacement string. To use this feature, you should use brackets to wrap any elements of your regular expression that you might want to use. The text matched with two backslashes and the number of the atom (\\1, for example). Atoms are match. by these subpatterns will be available to the replacement string if you refer to them numbered in order, outer to inner, left to right starting at \\1. \\0 stores the entire No The following fragment converts dates in dd/mm/yy format to mm/dd/yy format: $test = "25/12/2000"; print ereg_replace("([0– 9]+)/([0– 9]+)/([0– 9]+)", "\\2/\\1/\\3", $test); // prints "12/25/2000" Note ereg_replace() is case sensitive. If you don't want to match case, you can use eregi_replace(), which is not case sensitive but is identical to tf or co m er Back references make it possible for you to use part of a matched pattern in the cia l, Using Back References with egrep_replace() http://i-tronics.blogspot.com/ us will find and replace every instance of a pattern. e Note that although ereg() will only match the first pattern it finds, ereg_replace() fo re du ca tio egrep_replace() returns a string, including the modification if a match was found or n the text with which to replace a found pattern, and the text to modify. on ly Until now we have searched for patterns in a string, leaving the search string 343 ereg_replace() in all other respects. Using split() to Break Up Strings In Hour 17, you saw that you could split a string of tokens into an array using used as a delimiter. PHP4's split() function enables you to use the power of regular expressions to define a flexible delimiter. split() requires a string representing a pattern to use as a delimiter and a source string. It also accepts an optional third returns an array. The following fragment uses a regular expression with two branches to split a string on either a comma followed by a space or the word and surrounded by two spaces: $text = "apples, oranges, peaches and grapefruit"; $fruitarray = split( ", | and ", $text ); foreach ( $fruitarray as $item ) print "$item<BR>"; // output: // apples // oranges // peaches // grapefruit Perl Compatible Regular Expressions (PCREs) If you are migrating from Perl to PHP, you are likely to find the POSIX regular Perl compatible regular expressions. PCREs are even more powerful than the syntax that you have already examined. We will explore the differences in this section. Matching Patterns with preg_match() No preg_match() accepts three arguments: a regular expression, a source string, and an array variable, which will store matches. preg_match() returns true if a match is tf expression functions somewhat cumbersome. The good news is that PHP4 supports or co m er cia l, http://i-tronics.blogspot.com/ us e fo re du ca tio argument representing a limit to the number of elements you want returned. split() n on ly explode(). This is powerful but limits you to a single set of characters that can be 344 found and false otherwise. The difference between this function and ereg_match() lies in the regular expression argument. Perl compatible regular expressions s hould be enclosed by delimiters. Conventionally, these delimiters are forward slashes, although you can use any character that isn't alphanumeric (apart from the backslash character). The following fragment uses preg_match() to match the character p followed by any character, followed by the character t: $text = "pepperpot"; if ( preg_match( "/p.t/", $text, $array ) ) print $array[0]; // prints "pot" PCREs and Greediness By default, regular expressions will attempt to match as many characters as possible. So, "/p.*t/" will find the first "p" in a string and match as many characters as possible until the last possible "t" character is reached. So, this regular expression matches the entire test string in the following fragment: $text = "pot post pat patent"; if ( preg_match( "/p. *t/", $text, $array ) ) print $array[0]; // prints "pot post pat patent" By placing a question mark (?) after any quantifier, you can force a Perl compatible "p.*t" No means "p followed by as many characters as possible followed by t," "p.*?t" means "p followed by as few characters as possible followed by t," The following fragment uses this technique to match the smallest number of characters starting with "p" and ending with "t": $text = "pot post pat patent"; http://i-tronics.blogspot.com/ tf or regular expression to be more frugal. So, whereas co m er cia l, us e fo re du ca tio n on ly 345 if ( preg_match( "/p. *?t/", $text, $array ) ) print $array[0]; // prints "pot" PCREs and Backslashed Characters You can escape certain characters with Perl compatible regular expressions, just as you can within strings. \t, for example represents a tab character, and \n represents a newline. PCREs also define some escape characters that will match entire character types. Table 18.2 lists these backslash characters. Table 18.2: Escape Characters That Match Character Types Character \d Matches \D e \s us cia l, \S m er co or \w tf No \w http://i-tronics.blogspot.com/ fo re du ca Any number Anything other than a number Any of whitespac e Anything other than whitespac e Any word character (including the underscor e character) Anything other than kind tio n on ly 346 a word character These escape characters can vastly simplify your regular expressions. Without them, you would be forced to use a character class to match ranges of characters. Compare the ereg() and preg_match() syntax for matching word characters: ereg( "p[a– zA– Z0– 9_]+t", $text, $array ); preg_match( "/p\w+t/, $text, $array ); match positions within a string, without matching any characters. These are listed in Table 18.3: Escape Characters That Act as Anchors Character \A \b \B us e cia l, \Z m er co or tf No \z http://i-tronics.blogspot.com/ fo re du ca Matches Beginning of string Word boundary Not word boundary End string (matches before final newline or at end of string) End string (matches only at very end of string) of of a Table 18.3. tio n PCREs also support a number of escape characters that act as anchors. Anchors on ly 347 Remember the problems we had matching word boundaries in our membership code example? PCREs make this job much easier. Compare the ereg() and preg_match() syntax for matching word characters and boundaries: ereg( "(^|[^a-zA-Z0-9_])(p[a-zA-Z0-9_]+t)([^a-zA-Z0-9_]|$)", $text, $array ); preg_match( "\bp\w+t\b", $text, $array ); The preg_match() call in the previous fragment will match the character "p" but only if it is at a word boundary, followed by any number of word characters, followed by not actually match a character; it merely confirms that a boundary exists for a match to take place. For the ereg_match() call, you must construct a pattern for a nonword character and match either that or a string boundary. "t," but only if it is at a word boundary. The word boundary escape character does You can also escape characters to turn off their meanings. To match a "." character, for example, you should add a backslash to it. Finding Matches Globally with preg_match_all() every instance of a pattern within a string. So, using ereg() to search for words beginning with "p" and ending with "s", we will match only the first found pattern. $text = "I sell pots, plants, pistachios, pianos and parrots"; $text, $array ) ) for ( $x=0; is_string( $array[$x] ); $x++ ) No // output: // $array[0]: pots, // $array[1]: // $array[2]: pots // $array[3]: , tf } or print "\$array[$x]: $array[$x]<br>\n"; co { m er if ( ereg( "(^|[^a-zA-Z0-9_])(p[a-zA-Z0-9_]+s)([^a-zA-Z0-9_]|$)", cia l, Let's try it out: http://i-tronics.blogspot.com/ us e One of the problems with POSIX regular expressions is that it is difficult to match fo re du ca tio n on ly 348 As we would expect, the first match, "pots", is stored in the third element of the $array array. The first element contains the complete match, the second contains a space, and the fourth contains a comma. To get at every pattern match in our test string, we would have to use ereg_replace() in a loop to remove each match from the string before testing again. preg_match_all() accepts a regular expression, a source string, and an array variable, and will return true if a match is found. The array variable is populated with complete pattern defined in the regular expression. a multidimensional array, the first element of which will contain every match to the output the multidimensional array of results. Listing 18.1: Using preg_match_all() to Match a Pattern Globally 1: <html> 2: <head> 5: <body> 6: <?php 7: $text = "I sell pots, plants, pistachios, pianos and parrots"; 8: if ( preg_match_all( "/\bp\w+s\b/", $text, $array ) ) 9: 10: 11: 12: 13: { for ( $x=0; $x< count( $array ); $x++ ) { tf or No 14: 15: } 16: // Output: 17: // $array[0][0]: pots 18: // $array[0][1]: plants co for ( $y=0; $y< count( $array[$x] ); $y++ ) print "\$array[$x][$y]: ".$array[$x][$y]."<BR>\n"; } m er cia l, http://i-tronics.blogspot.com/ us 4: </head> e 3: <title>Using preg_match_all() to match a pattern globally</title> fo re du ca Listing 18.1 tests a string using preg_match_all(), using two for statements to tio n on ly We can use preg_match_all() to access every match in the test string in one call. 349 19: // $array[0][2]: pistachios 20: // $array[0][3]: pianos 21: // $array[0][4]: parrots 22: ?> 23: </body> 24: </html> The first and only element of the $array variable that we passed to preg_match_all() test string that begins with "p" and ends with "s". preg_match_all() populates a multidimensional array to store matches to subpatterns. The first element of the array argument passed to preg_match_all() will contain every match of the complete regular expression. Each additional element will contain the matches that correspond to each atom (subpattern in brackets). So with the following call to preg_match_all() preg_match_all( "/(\d+)-(\d+)-(\d+)/", $text, $array ); $array[0] will store an array of complete matches: $array[0][0]: 01-05-99 $array[0][1]: 01-10-99 $array[0][2]: 01-03-00 $array[1] will store an array of matches that corresponds to the first subpattern: No $array[1][2]: 01 $array[2] will store an array of matches that corresponds to the second subpattern: $array[2][0]: 05 $array[2][1]: 10 $array[2][2]: 03 and so on. http://i-tronics.blogspot.com/ tf $array[1][1]: 01 or $array[1][0]: 01 co m er cia l, us $text = "01-05-99, 01-10-99, 01-03-00"; e fo re du ca has been populated with an array of strings. This array contains every word in the tio n on ly 350 Using preg_replace() to Replace Patterns preg_replace() behaves in the same way as ereg_replace(), except that you have access to the additional functionality of Perl compatible regular expressions. string. If a match is found, it returns a transformed string; otherwise, it returns a dd/mm/yy to mm/dd/yy format: $t = "25/12/99, 14/5/00"; preg_replace() requires a regular expression, a replacement string, and a source copy of the source string. The following fragment transforms dates in a string from print "$t<br>"; // prints "12/25/99, 5/14/00" Notice that we have used a pipe (|) symbol as a delimiter. This is to save us from having to escape the forward slashes in the pattern we want to match. preg_replace() supports back references in the same way as ereg_replace(). will transform each string in turn. In this case, the return value will be an array of You can also pass arrays of regular expressions and replacement strings to corresponding replacement string will be applied. The following fragment transforms date formats as before, but also changes copyright information in the source string: $text = "25/12/99, 14/5/00. Copyright 1999"; $regs = array( "|\b(\d+)/(\d+)/(\d+)\b|", $reps = array( "\\2/\\1/\\3", or co m er preg_match(). Each regular expression will be applied to the source string, and the cia l, transformed strings. us Instead of a source string, you can pass an array of strings to preg_match(), and it tf No $text = preg_replace( $regs, $reps, $text ); print "$text<br>"; // prints "12/25/99, 5/14/00. Copyright 2000" We create two arrays. The first, $regs, contains two regular expressions, and the second, $reps, contains replacement strings. The first element of the $reps array corresponds to the first element of the $reps array, and so on. http://i-tronics.blogspot.com/ e fo re du ca "\\1 2000" ); $t = preg_replace( "|\b(\d+)/(\d+)/(\d+)\b|", "\\2/\\1/\\3", $t ); "/([Cc]opyright) 1999/" ); tio n on ly 351 If the array of replacement strings contains fewer elements than the array of regular expressions, patterns matched by those regular expressions without corresponding replacement strings will be replaced with an empty string. If you pass preg_replace() an array of regular expressions but only a string as replacement, the same replacement string will be applied to each pattern in the array of regular expressions. Modifiers Perl compatible regular expressions allow you to modify the way that a pattern is NEW TERM A pattern modifier is a letter that should be placed after the final delimiter in your Perl compatible regular expression. It will refine the behavior of your regular expression. Table 18.4 lists the PCRE pattern modifiers Table 18.4: Perl Compatible Regular Expression Modifiers /i /e us e Pattern cia l, fo re du ca string match applied through the use of pattern modifiers. tio PHP code. Matches (newlines normally readability. Description Case insensitive. Treats replacement in as preg_replace() /m m er $ and ^ anchors the beginning and end of the current line. newlines are not not No tf /s or co matched by. ). Whitespace outside character classes is not matched to aid To /x http://i-tronics.blogspot.com/ n on ly 352 match whitespace, use \s, \t, or \. /A Matches only at pattern start of string (this modifier /E Matches only at end of string fo re du ca m /U tio expression allowable found in Perl). Makes the regular ungreedy— minimu number of matches found (this modifier is not found in Perl). might want to use the x modifier to make your regular expression easier to read, for \S* t /ix will match "bat" and "BAT" but not "B A T", for example. Unescaped spaces in a regular expression modified by x are there for aesthetic reasons only and will not match any patterns in the source string. The m modifier can be useful if you want to match an anchored pattern on multiple lines of text. The anchor patterns ^ and $ match the beginning and ends of an entire string by default. The following fragment uses the m modifier to change the No preg_match_all( "/^\w+:\s+(.*)$/m", $text, $array ); foreach ( $array[1] as $val ) print "$val<br>"; // output: // matt // coder tf $text = "name: matt\noccupation: coder\neyes: blue\n"; or behavior of $: co m er cia l, example, and also the i modifier to make it match patterns regardless of case. / b http://i-tronics.blogspot.com/ us Where they do not contradict one another, you can combine pattern modifiers. You e n (this modifier is not on ly pattern is not found in Perl). 353 // blue We create a regular expression that will match any word characters followed by a colon and any number of space characters. We then match any number of characters followed by the end of string ($) anchor. Because we have used the m pattern modifier, $ matches the end of every line rather than the end of the string. The s modifier is useful when you want use . to match characters across multiple lines. The following fragment attempts to access the first and last words of a string: This code will print nothing. Although the regular expression will find word characters at the beginning of the string, the . will not match the newline characters embedded in the text. The s modifier will change this: $text = "start with this line\nand you will reach\na conclusion in the end\n"; preg_match( "/^(\w+).*?(\w+)$/s", $text, $array ); // prints "start end" string in preg_replace() as if it were PHP. You can pass back references to functions as arguments, for example, or process lists of numbers. In the following example we use the e modifier to pass matched numbers in dates to a function that returns the same date in a new format. function convDate( $month, $day, $year ) { No $dates = "3/18/99<br>\n7/22/00"; $dates = preg_replace( "/([0– 9]+)\/([0– 9]+)\/([0– 9]+)/e", http://i-tronics.blogspot.com/ tf $time = ( mktime( 0,0,0,$month,$day,$year) ); return date("1 F Y", $time); } or $year = ($year < 70 )?$year+2000:$year; co <?php m er cia l, The e modifier can be particularly powerful. It allows you to treat the replacement us e print "$array[1] $array[2]<br>"; fo re du ca print "$array[1] $array[2]<br>"; tio preg_match( "/^(\w+).*?(\w+)$/", $text, $array ); n $text = "start with this line\nand you will reach\na conclusion in the end\n"; on ly 354 "convDate(\\1,\\2,\\3)", $dates); print $dates; // prints: // Thursday 18 March 1999 // Saturday 22 July 2000 ?> We match any set of three numbers separated by slashes, using parentheses to user-defined function convDate() from the replacement string argument, passing input and produces a more verbose date which replaces the original. Summary Regular expressions are a huge subject, and we've really only scraped the surface of their power in this hour. Nevertheless, you should now be able to use regular expression functions to find and replace complex patterns in text. You should be able to use the ereg() regular expression function to find patterns in string. You should be able to find ranges of characters using character classes, multiple patterns using quantifiers, and alternative patterns using branches. You the aid of Perl compatible regular expressions, you should be able to use escape characters to anchor patterns or to match character types. You should be able to use modifiers to change the way in which PCREs work. No Q Perl compatible regular expressions seem very powerful. Is there anywhere I can find out more about them? A The relevant section in the PHP manual at http://www.php.net will offer some information about regular expression syntax. You can also find some useful information at http://www.perl.com— in particular, an introduction to Perl regular expressions at http://www.perl.com/pub/doc/manual/html/pod/perlre.html and an tf Q&A or co m er should be able to extract subpatterns and refer to them with back references. With cia l, strings and the ereg_replace() function to replace all instances of a pattern in a http://i-tronics.blogspot.com/ us e fo re du ca the three back references to the function. convDate() simply takes the numerical tio n capture the matched numbers. Because we are using the e modifier, we can call the on ly 355 article by Tom Christiansen at http://www.perl.com/pub/doc/manual/html/pod/perlfaq6.html. Workshop material covered. Try to understand the quiz answers before continuing to the next hour's lesson. Quiz answers are provided in Appendix A. Quiz Using POSIX regular expression functions, what function would you use to match a pattern in a string? once but not more than six times? What regular expression syntax would you use to match the letter "b" at least How would you specify a character range between "d" and "f"? How would you negate the character range you defined in question 3? What syntax would you use to match either any number or the word "tree"? What POSIX regular expression function would you use to replace a matched pattern? The regular expression .*bc will match greedily— that is, it will match "abc000000bc" rather than "abc". Using Perl compatible regular expressions, how would you make the preceding regular expression match only the first instance of a pattern it finds? What PCRE