PHP session problems

Question

I am using the following code to invalidate the session. I have linked to logout.php in many pages. If that logout link is clicked the logout.php page is called. The following is the code in logout.php.

unset($_SESSION['admin']);
session_destroy();
header('Location: index.php');

Once the session is invalidated I want to open the page index.php. But I am geting the following error:

Warning: session_destroy() [function.session-destroy]: Trying to destroy uninitialized session in C:\xampp\htdocs\Selection\logout.php on line 3

Warning: Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\Selection\logout.php:3) in C:\xampp\htdocs\Selection\logout.php on line 4

What is wrong?

Answer 1

I think that you don't have called the session_start() function before destroy the session.

Answer 2

You`ll need to call session_start() on top of the page to remind php that this pagecall belongs to the session. - At least PHP manual tells that.

The notes on that manual page give hint, that session_unset() is only to be used in older environments that are not using $_SESSION variable.

Answer 3

You have to open the session first:

header('Location: index.php');
session_start();
session_unset();
session_destroy();

Answer 4

The problem is that you can't destroy a session which hasn't been started. That is then raising a warning which is being echoed to the browser. The next problem is that you can't send headers after there's been output to the browser, so it raises another warning.

You just need to check if a session exists first:

if (session_name() != '') {
    session_destroy();
}

Answer 5

You must ALWAYS use session_start(); BEFORE using a session function/variable. So start all PHP files with session_start();. Also logout.php:

session_start();
session_destroy();
header('Location: index.php');

You also don't need to unset it.