Error Cannot modify header information - headers already sent by output started at some file php 12 in some file php on line 23

Question

When running my script, I am getting several errors like this:

Warning: Cannot modify header information - headers already sent by (output started at /some/file.php:12) in /some/file.php on line 23

The lines mentioned in the error messages contain header() and setcookie() calls.

What could be the reason for this? And how to fix it?

Answer 1

Hello @kartik,

This error message gets triggered when anything is sent before you send HTTP headers. Common reasons for outputting something before the HTTP headers are:

Accidental whitespace, often at the beginning or end of files, like this:

 <?php
// Note the space before "<?php"
?>

To avoid this, simply leave out the closing ?> - it's not required anyways.

Hope it helpss!!
ThanK you!!