PHP headers_sent() function usage and example

PHP HTTP 　reference manual

The headers_sent() function checks if the HTTP header has been sent.

Syntax

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

Definition and usage

Check if the HTTP header has been sent.
When the HTTP header has been sent, it is not possible to add more header fields through header(). Using this function at least can prevent HTTP header errors. Another solution is to use output buffering.

Return value

　When the HTTP header has not been sent, headers_sent() returns FALSE, otherwise it returns TRUE.

Parameter

Online example

Try the following example

<?php
　　　if (!headers_sent()) {
　　　　　　header('Location: http://ru.oldtoolbag.com/');
　　　　　　exit;
　　　}
　　　
　　　if (!headers_sent($filename, $linenum)) {
　　　　　　header('Location: http://ru.oldtoolbag.com/');
　　　　　　exit;
　　　} else {
　　　　　　echo \
　　　　　　　　　
　　　　　　　　　"href = \
　　　　　　exit;
　　　}
?>

The following example checks if the header has been sent, if it has been sent, a message is displayed, otherwise the header is sent

PHP HTTP 　reference manual