Page redirect help !

[tamucq]

Hello guys, cn anyone share me a redirect sc that can be used for redirecting user back to login page if they have wrong username and password pls ?

I've tried used header();
Error show, cannot modify header already send by output

Added after 3 minutes:

Also have tried this code that i found from other sites 'location.replace()' but useless

[something else]

you have to use the header before any other headers eg:
At top of page:

if(not_logged_in){
header('Location: login.php');
exit;
} 

[doriann]

use the reader location bro

[tamucq]

you have to use the header before any other headers eg:
At top of page:

if(not_logged_in){
header('Location: login.php');
exit;
} 

tq bro the code work fine on ma lava sc