PHP重定向是否适用于页面顶部？

Question

I am following along with a Lynda.com tutorial on php and am learning about php redirects. Using header("Location: basic.html"), the tutor says for a redirect to work it must be the very first thing on a page. However, I tested that by putting the php code within the tags and the redirect still worked. I have looked at other online resources and they too say that there should be nothing above the redirect. Are the resources I have looked at simply out of date or am I missing a point here?

Thanks

I am running XAMPP on my local machine. My code is: Redirect

<?php
// This is how you redirect to a new page
    function redirect_to($new_location) {
        header("Location: " . $new_location);
            exit;       
    }

    $logged_in = $_GET['logged_in'];

    if($logged_in == 1) {
    redirect_to("basic.html");
    } else {
        redirect_to("http://www.google.co.uk");
    }
    ?>

</body>

Answer 1

This depends on the server for the output method. The server could either start delivering the PHP output as it is computed or only after the whole output is ready. If there was any output sent to the client you can't send an HTTP redirect header anymore.

However you can suppress the output in PHP itself using the output buffering functions. See: http://php.net/manual/en/ref.outcontrol.php