Cannot modify header information - headers already sent

Hello!

I used the following couple of lines to redirect to a page:

header("Location:index.php?ad_detail=1&ad_id=".$adId);
exit();

It shows:
Cannot modify header information - headers already sent

Then, I used the following couple of lines to redirect to a page:

header("location:index.php?contact_us=1");
exit();

It also shows:
Cannot modify header information - headers already sent

Finally, I used the following couple of lines to redirect to a page:

header("location:index.php");
exit();

It also shows:
Cannot modify header information - headers already sent


Is there any solution?
Please help me out ASAP

 

You must have no 'echo' output before header, no spaces before php tags, no html code before header sent.

 

<?php
ob_start();
//put the rest of your code here
ob_end_flush();
?>

PHP:

will insure that no header is sent until all your code is processed.