PHP headers_sent() function usage and example

PHP HTTP Reference Manual

The headers_sent() function detects whether the HTTP header has been sent.

Syntax

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

Definition and Usage

Detect 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 prevents 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: \//www.oldtoolbag.com/');
　　　　　　exit;
　　　}
　　　
　　　
　　　　　　header('Location: \//www.oldtoolbag.com/');
　　　　　　exit;
　　　} else {
　　　　　　echo \
　　　　　　　　　
　　　　　　　　　"href = \//www.oldtoolbag.com\">link</a> instead
";
　　　　　　exit;
　　　}
?>

The above 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