Checks if or where headers have been sent

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- PHP Manual
- Network Functions
- Checks if or where headers have been sent

# headers_sent

(PHP 4, PHP 5, PHP 7, PHP 8)

headers_sent — Checks if or where headers have been sent

### Description

headers_sent(string `&$filename` = `null`, int `&$line` = `null`): bool

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

Example #1 Examples using headers_sent()

    <?php// If no headers are sent, send oneif (!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

> Note:

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

### See Also

- ob_start() - Turn on output buffering
- trigger_error() - Generates a user-level error/warning/notice message
- headers_list() - Returns a list of response headers sent (or ready to send)
- header() - Send a raw HTTP header for a more detailed discussion of the matters involved.