PHP 5.6.0RC3 is available

session_unset

(PHP 4, PHP 5)

session_unsetFree all session variables

Description

void session_unset ( void )

The session_unset() function frees all session variables currently registered.

Return Values

No value is returned.

Notes

Note:

If $_SESSION (or $HTTP_SESSION_VARS for PHP 4.0.6 or less) is used, use unset() to unregister a session variable, i.e. unset ($_SESSION['varname']);.

Caution

Do NOT unset the whole $_SESSION with unset($_SESSION) as this will disable the registering of session variables through the $_SESSION superglobal.

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User Contributed Notes 8 notes

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7
Anonymous
13 years ago
To further clarify the note above... this can be done via the session handling directives in your php.ini file... there are options to set garbage collection probability (via percent... i.e. 75 means it would run 3 out of every 4 page accesses), and the amount of time a session object can remain active before the garbage collection process sees it as garbage.
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3
Jeroen
9 years ago
note to Jason: I don't know the exact mechanics of it (since I'm quite new to sessions) but I think you need to use session_unset() BEFORE you can use session_destroy() at all.  I thought that session_unset() was for scripted variables, and session_destroy() just for anything saved on your side regarding the session.
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2
notsonewbie
3 years ago
dash2nash: you have to start the session before you can unset or destroy it.
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1
tim at leethost dot com
2 years ago
I was having a problem clearing all session variables, deleting the session, and creating a new session without leaving old session stuff behind in all browsers.  The below code is perfect for a logout script to totally delete everything and start new.  It even works in Chrome which seems to not work as other browsers when trying do logout and start a new session.

<?php
    session_start
();
   
session_unset();
   
session_destroy();
   
session_write_close();
   
setcookie(session_name(),'',0,'/');
   
session_regenerate_id(true);
?>
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-4
mwgamera at gmail dot com
1 year ago
There is nothing magical about the $_SESSION superglobal and unsetting it.
One has simply to remember that all the session_* functions will use continue to
use exactly that instance of array that was set up by session_start.

Consider this example:
<?php
session_start
();
var_dump($_SESSION);
$a =& $_SESSION;
unset(
$_SESSION);
$a['x'] = 1; // $a refers to the original $_SESSION
$_SESSION['x'] = 2; // new unrelated array
session_write_close();
// saved session contains x => 1
?>
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-6
zach at zkwarta dot com
9 years ago
The difference between both session_unset and session_destroy is as follows:

session_unset just clears out the sesison for usage. The session is still on the users computer. Note that by using session_unset, the variable still exists.

Using session_unset in tandem with session_destroy however, is a much more effective means of actually clearing out data. As stated in the example above, this works very well, cross browser:

session_unset();
session_destroy();

I noticed that in firefox, one could simply use sesison_unset and the session would be cleared. When trying this on IE, I was horrified to find out that the data was still there, so I had to use session destroy.
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-8
dash2nash
3 years ago
Im using chrome and Im not a pro in php, but Im certainly sure that session sure is buggy on google chrome, I use:

    session_unset();
    session_destroy();
    $_SESSION = array();
    session_start();

every time the page load, yet, some of the session still there. It's quite scary problem :s
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-9
00 at f00n dot com
6 years ago
-------------------------------------------------------
InterNic
20-May-2006 11:20
sometimes you might have problems even if using both session_unset and session_destroy. You have to clear the $_SESSION array. I got it working this way:

session_unset();
session_destroy();
$_SESSION = array();
-------------------------------------------------------

When I used this method the session still existed in structure until the array is reset completely.

This, however, has the drawback of clearing all sessions which may not be ideal in some cases.

Named sessions may help in such cases.
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