Checks if or where headers have been sent.
You can't add any more header lines using the header() function once the header block has already been sent. Using this function you can at least prevent getting HTTP header related error messages. Another option is to use Output Buffering.
If the optional file
and line
parameters are set, headers_sent() will put the PHP source file name and line number where output started in the file
and line
variables.
The line number where the output started.
headers_sent() will return FALSE
if no HTTP headers have already been sent or TRUE
otherwise.
Headers will only be accessible and output when a SAPI that supports them is in use.
<?php // If no headers are sent, send one if (!headers_sent()) { header('Location: http://www.example.com/'); exit; } // An example using the optional file and line parameters, as of PHP 4.3.0 // Note that $filename and $linenum are passed in for later use. // Do not assign them values beforehand. if (!headers_sent($filename, $linenum)) { header('Location: http://www.example.com/'); exit; // You would most likely trigger an error here. } else { echo "Headers already sent in $filename on line $linenum\n" . "Cannot redirect, for now please click this <a " . "href=\"http://www.example.com\">link</a> instead\n"; exit; } ?>
header() -
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