Cannot modify header information Warning message in PHP?

Question

php code-

$q = "Update tblarticle set art_title='$title', art_cat='$cat', art_des='$txtart' where art_id='".$_GET['art_id']."'";
$result = $mysqli->query($q) or die(mysqli_error($mysqli));
if($result)
{
    //saved succesfullt
    $error =0;
    header("location:mngArt.php");
    exit;
}
else $error =1;
}
?>  
....Some HTML........

database is getting updated but Cannot modify header information error msg is popping up.

Answer 1

There cannot be anything outside the closing PHP tag if you want to modify the headers. So the HTML outside the ?> will be causing that warning.

Answer 2

The reason is that at some point something is output to the screen. This could be anything from a full website to a tiny space or newline character(s).

Important: Unlike what MRW said, there must not be any HTML before calling that function. After calling it, you can do anything you want.

So it is the code before <?php that is the issue, not the one after ?>.

Answer 3

The easiest way to fix it is to add this to the very top of your file:

<?php
ob_start();