session_unset()

(PHP 4, PHP 5, PHP 7)

释放所有的会话变量

说明

session_unset()会释放当前会话注册的所有会话变量。

返回值

没有返回值。

注释

如果使用的是$_SESSION(或者PHP 4.0.6或更早版本的$HTTP_SESSION_VARS)，请使用unset()去注销会话变量，即unset ($_SESSION['varname']);.Caution

请不要使用unset($_SESSION)来释放整个$_SESSION，因为它将会禁用通过全局$_SESSION去注册会话变量

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. 

The difference between both session_unset and session_destroy is as follows:
session_unset just clears out the session for usage. The session is still on the users computer. Note that by using session_unset, the variable still exists. session_unset just remove all session variables. it does not destroy the session....so the session would still be active.
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_destroy is destroy the session. session_destroy() to kill all session information.....This is the more secure function to use.

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.

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.

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: 

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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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();
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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.

While CLI session_unset() doesn't work (it doesn't clear session variables).
Using CLI you must use: 

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