headers_sent

Description

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

filename

If the optional filename and line parameters are set, headers_sent() will put the PHP source file name and line number where output started in the filename and line variables.

Note

If the output has started before executing the PHP source file (for example due to a startup error), the filename parameter will be set to an empty string.

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.

Examples

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
// 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 Sapi

See Also

• ob_start()
• trigger_error()
• headers_list()
• header() for a more detailed discussion of the matters involved.