Reading queued headers

array headers_list ( void )

We already looked at the headers_sent() function, which tells us whether or not HTTP headers have already been sent to the client. This function duplicates that functionality, but, crucially, also returns headers that have yet to be sent, which when you think about it is a bit more useful.

As you can see from the prototype, it takes no parameters, and returns an array. That array contains a numerically indexed list of the headers that are ready for sending, which means we can extend our previous example like this:

<?php
    header("Expires: Sat, 22 Dec 1979 05:30:00 GMT");
    echo "This is some text for output.<br />";
    
    if (!headers_sent($filename, $linenum)) {
        // if no headers have been sent, send one
        // this will not execute, as we sent the Expires header.
        header("Location: www.yoursite.com");
        exit;
    } else {
        echo "Headers already sent in $filename on line $linenum.<br />";
        echo "Headers sent are:<br /> <UL>";

        $headers = headers_list();
        foreach($headers as $header) {
            echo "<LI>$header</LI>";
        }

        echo "</UL>";

        exit;
    }
?>

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