警告：session_destroy（）？

Question

Im trying to fix my login script, on my localhost it works but uploaded to my online test server, the logout is broken, I get this error:

Warning: session_destroy() [function.session-destroy]: Trying to destroy uninitialized session in htdocs/logout.php on line 17

Warning: Cannot modify header information - headers already sent by (output started at htdocs/logout.php:17) in htdocs/logout.php on line 18

Warning: Cannot modify header information - headers already sent by (output started at htdocs/logout.php:17) in www/htdocs/logout.php on line 34

Not quite sure what could be causing it since it was working on my localhost, any ideas?

Answer 1

session_start();
session_destroy(); /*or sesion_unset();*/

Answer 2

要使session_destroy工作，必须使用session_start启动会话。

Answer 3

If you need to just delete the session if it exists (for example in an auto called exit/logout/destructor script) and it may or may not exist, then you can use session_status to check the status.

As of PHP 5.4.0, you can check it like this:

if(session_status() == PHP_SESSION_ACTIVE)
{
    session_destroy();
}

This is preferable to creating a new section just to destroy it later.

Per the PHP manual, session_status will return an integer that can be compared with the following constants:

Return Values 

• PHP_SESSION_DISABLED - Returned if sessions are disabled. 
• PHP_SESSION_NONE - Returned if sessions are enabled, but none exists. 
• PHP_SESSION_ACTIVE - Returned if sessions are enabled, and one exists. 

This allows you to write better, more efficient, and more flexible session management code.