Destroying Sessions and Session Variables

To end a session, and destroy all session variables, use the function: session_destroy(). The next page you go to will no longer have access to the session variables. The variables will still be available in the script where you called session_destroy(). To remove all the session_variables immediately, use the the function session_unset(). Individual session variables can either be unset with unset() (for $_SESSION["varname"]), or by calling the function session_unset() if you used session_register() to set the variable. Look at this example:

<?php
	session_start();
	$_SESSION["firstname"] = "TimeIsUp";
	session_destroy();
?>
Click here to <a href="page9.php?<?=SID?>">Forget the name</a>

<?php
	session_start();
	print "Your firstname is: ".$_SESSION["firstname"]." ,or is it?";
?>

The firstname does not appear, as page8.php called session_destroy(). However, if we moved session_destroy() to page9.php, the variables would still be available in that page, as follows:

<?php
	session_start();
	$_SESSION["firstname"] = "IsTimeUp?";
?>
Click here to <a href="page11.php?<?=SID?>">try forget the name</a>

<?php
	session_start();
	session_destroy();
	print "Your firstname is: ".$_SESSION["firstname"];
?>

This time the name is remembered. However, click refresh once on page11.php, and the firstname will disappear, as the session was destroyed the first time you loaded page11.php. To see session_unset() in action, we take the identical 2 scripts, except that page13.php calls session_unset() immediately before it calls session_destroy(), clearing the session variables.

<?php
	session_start();
	$_SESSION["firstname"] = "TimeIsUp";
?>
Click here to <a href="page13.php?<?=SID?>">forget the name</a>

<?php
	session_start();
	session_unset();
	session_destroy();
	print "Your firstname is: ".$_SESSION["firstname"];
?>

We could also replace session_unset() with unset (or session_unregister(firstname) if you're using session_register), and achieve the same effect. session_unset() clears all the session variables, session_unregister() just what is passed to the function. Since we only have the one variable, the effect is the same, as you would discover if you run the following script in the same way, clicking from page12.php.

<?php
session_start();
	session_start();
	unset($_SESSION["firstname"]);
	// if you're using session_register, the function to call is:
	// session_unregister(firstname);
	session_destroy();
	print "Your firstname is: $firstname";
?>
 

Session Variables
Maintaining state with PHP4 sessions
Encoding session variables