PHP Redirect?

I am having trouble saying if a variable in the session is not set then redirect back to the login page any help would be great thank you

<?php session_start(); 

if(!isset($_SESSION['username']))
  {
       header("Location: login.php"); 
  } 
?>

Code (markup):

This doesn't work any thoughts?

 

I don't see why your code shouldn't work :/
try print_r($_SESSION) on the session, to check if its been set or not..

 

This is the error that I get:

Warning: Cannot modify header information - headers already sent by (output started at /home/mofiki/public_html/testsite/header.php:3) in /home/mofiki/public_html/testsite/header.php on line 6

 

Ah, the reason its not working is because headers have to be declared before any other content is echoed out or something..
try putting it at the top of the script & including header.php and stuff after

 

Got it thank you very much for your quick replies it works great now .... the little issues are always the most annoying