Entry

Warning: Cannot add header information - headers already sent by xyz.php

May 27th, 2002 20:22
Deepak Kumar Vasudevan, Ashar Iqbal, PHP Manual

The default property of Zend Engine (PHP) is output buffering off. You 
can turn on output buffering programmatically at the start of PHP page, 
before even you try to send any HTML output by calling the function
ob_start()
If this is enabled, you may send HTTP headers even after HTML output 
has been sent.