PHP Manual: Checks if or where headers have been sent

Description

bool headers_sent ([ string &$file [, int &$line ]] )

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.

Parameters

file: 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.
line: The line number where the output started.

Return Values

headers_sent will return FALSE if no HTTP headers have already been sent or TRUE otherwise.

Changelog

Version	Description
4.3.0	The optional `file` and `line` parameters were added.

Examples

Example #1 Examples using headers_sent


<?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;
}

?>

Notes

Note:
Headers will only be accessible and output when a SAPI that supports them is in use.

headers_sent