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Working with Forms in PHP

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PHP code is usually embedded in HTML pages. For this reason it provides near transparent techniques for accessing data sent via HTML forms. This lesson covers the basics of gathering user input, and looks at some techniques for creating scripts that use forms.

Writing an introduction to any programming language is a challenge. It's difficult to balance the need to explain the foundations of a language with the understandable desire of the reader to jump in and get creative. Add to this the fact that many readers will have already suffered the familiar "what is a variable?" elsewhere, and the task can seem all but impossible. Omit the basics and you might leave the first time programmer confused and helpless; concentrate too much on the building blocks, and you risk frustrating the eager beavers.

With "Sams Teach Yourself PHP in 24 Hours," I have worked hard to get the learning curve right. Parts I and II offer the necessary boot camp to get new programmers up and running. That's not to say that it's all basic syntax. From installation and "Hello World" we quickly reach some of the more advanced features of the language, including arrays, functions, and even the basics of object oriented programming. Part III is the heart of the book. It's here that you will find out about the things that make PHP such a fantastic language for web programming. We cover techniques for creating database driven environments, for drawing images on the fly and manipulating text. We look at tricks for tracking users as they click through your Web environments and for recognizing them when they return. We even look at PHP's support for XML. In Part IV, we examine the ways that library code can be used to make PHP even more flexible and useful than it already is.

PHP is a renowned as an "easy" programming language, in that a coder can get impressive results fast. Because it's so friendly and forgiving, it can be easy to write bad code. With "Sams Teach Yourself PHP in 24 Hours," I have tried to help readers to tap into the strengths of PHP without making common mistakes that can haunt Web projects.

— Matt Zandstra

This chapter is from the book

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 information. In this hour, you will look at strategies for acquiring and working with 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 predefined 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

  • How to build HTML forms that upload files and how to write the PHP code to handle them

Predefined Variables

Before you actually build a form and use it to acquire data, you need to make a small detour and look again at global variables. You first met these in Hour 6, "Functions." 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 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: <html>
 2: <head>
 3: <title>Listing 9.1 Looping through the $GLOBALS array</title>
 4: </head>
 5: <body>
 6: <?php
 7: $user1 = "Bob";
 8: $user2 = "Harry";
 9: $user3 = "Mary";
10: foreach ( $GLOBALS as $key=>$value ) {
11:  print "\$GLOBALS[\"$key\"] == $value<br>";
12: }
13: ?>
14: </body>
15: </html> 

We declare three variables (lines 7-9) and then loop through the built-in $GLOBALS associative array (lines 10 and 11), writing both array keys and values to the browser. In the output, we are able to locate the variables we defined, but we see an awful lot more besides these. PHP automatically defines global variables that describe both the server and client environments. According to your system, server, and configuration, the availability of these variables will vary, but they can be immensely useful. Table 9.1 lays out some common predefined variables. These can be accessed as part of the $GLOBALS array, or directly.

Table 9.1 Some Predefined Variables

Variable

Contains

Example

$HTTP_USER_AGENT

The name and version of the client

Mozilla/4.6 (X11;I;Linux2.2.6-15apmac ppc)

$REMOTE_ADDR

The IP address of the client

158.152.55.35

$REQUEST_METHOD

Whether the request was GET or POST

POST

$QUERY_STRING

For GET requests, the encoded data send appended to the URL

name=matt&address=unknown

$REQUEST_URI

The full address of the request including query string

/matt/php-book/forms/eg9.14.html?name=matt

$HTTP_REFERER

The address of the page from which the request was made

http://www.test.com/a_page.html


In addition to these header-oriented variables, PHP makes some other global variables available to you. The variable $GLOBALS["PHP_SELF"], for example, gives you the path to the script currently running. On my system this was as follows:

/dev/php24/ch9/listing9.1.php

This variable can also be directly accessed as the global variable $PHP_SELF.

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