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

i trying set of pages forward login screen if user not logged in using session data, not working. when user clicks links continues new link opposed being forwarded login page. know session data cleared not issue. here's relevant code:

page headers:

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

login session declaration:

 $answer = mssql_fetch_array($res);     $_session['answer']=$answer[0]; 

logout:

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

in response on how on every other page:

i use required @ beginning of every secured php page on site. call "auth.php". if user not logged in(check via session variable), auth.php re-directs them login page.

if have header, great place put (if it's included in secured section, mine is).

my logout page destroys session , sends them login page.