Code to forward browser if user is not logged in (checking if session variable isset) is not firing

I am trying to set all of my pages to forward to the login screen if the user is not logged in using session data, however it is not working. When a user clicks the links it just continues to the new link as opposed to being forwarded to the login page. I know the session data is cleared so that is not the issue. Here's the relevant Code:

Page Headers:

 <?php
    session_start();
    if(!isset($_SESSION['answer']))
    {
        header('Location: /?login');
        exit;
    }?>

Login Session Declaration:

 $answer = mssql_fetch_array($res);
    $_SESSION['answer']=$an开发者_C百科swer[0];

Logout:

<?php
session_start();
session_destroy();
if(!isset($_SESSION['answer']))
{
    header('Location: /?login');
    exit;
}
?>

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session_destroy doesn't unset any global variables.

If you need to redirect unconditionally right after session destroy - just remove isset, you don't need it.

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In response on how to do this on every other page:

I use a required at the beginning of every secured php page on my site. I call it "auth.php". If the user is not logged in(check via session variable), the auth.php re-directs them to the login page.

If you have a header, this is a great place to put it (if it's only included in the secured section, which mine is).

My logout page destroys the session and sends them to the login page.