proper way to logout from a session in PHP

Question

I have read many php tutorials for logout scripts, i am wondering what could be the proper way to logout from a session!

Script 1

<?php
session_start();
session_destroy();
header("location:index.php");
?>

Script 2

<?php
session_start();
session_unset();
session_destroy();
header("location:index.php");
?>

Script 3

<?php
session_start();
if (isset($_SESSION['username']))
{
    unset($_SESSION['username']);
}
header("location:index.php");
?>

Is there any more effective way to do this?? A session can always be created by logging back in, so should i bother about use of session_destroy() and use unset($_SESSION['variable']) instead? which one of the above 3 script is more preferable?

Answer 1

From the session_destroy() page in the PHP manual:

<?php
// Initialize the session.
// If you are using session_name("something"), don't forget it now!
session_start();

// Unset all of the session variables.
$_SESSION = array();

// If it's desired to kill the session, also delete the session cookie.
// Note: This will destroy the session, and not just the session data!
if (ini_get("session.use_cookies")) {
    $params = session_get_cookie_params();
    setcookie(session_name(), '', time() - 42000,
        $params["path"], $params["domain"],
        $params["secure"], $params["httponly"]
    );
}

// Finally, destroy the session.
session_destroy();
?>