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Passing cookies between client and server

The one restriction on setting cookies in PHP is that it must be done before anything is output to the

client. This is similar to the way the

header()

function works. For instance, this code won’t work:

<html>

<head>

<?php

setcookie(“name”, “Nicholas”);

setcookie(“book”, “Professional JavaScript”);

To retrieve the value of a cookie in PHP, use the

$_COOKIE

associative array with the name of the cookie

as the key:

<?php

$name = $_COOKIE[“name”];

$book = $_COOKIE[“book”];

Note that you cannot retrieve the value of a cookie created with

setcookie()

until the next page loads,

meaning that is the following code is impossible:

<?php

setcookie(“name”, “Nicholas”);

setcookie(“book”, “Professional JavaScript”);

$name = $_COOKIE[“name”];

$book = $_COOKIE[“book”];

To delete a cookie in PHP, just use the

setcookie()

method and set the expiration time to

<?php

setcookie(“name”, “”, 0);

Passing cookies between client and server

To communicate to JavaScript, often the server creates a cookie (perhaps in a servlet or other application

running on the server) just before a response is sent out. The page that is loaded now has JavaScript

designed to retrieve the cookie value.

For example, suppose you are creating a feedback form on a Web site where the user is required to enter

a name, e-mail address, and the feedback message. You can make this more user-friendly by allowing

the users to save their names and e-mail addresses so the next time they visit and want to leave feed-

back, both fields are already filled in. Typically, you do this with a Remember Me check box, as in the

following form:

E-mail Address: <input type=”text” name=”personEmail” /><br />

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