Question

<?php
require 'header.php';
require 'connection.php';

mysql_query("DELETE FROM quotes WHERE ID = $_GET[id]") or die("didnt delete properly");
header('Location: index.php');
?>

When I run this it says:
Warning: Cannot modify header information – headers already sent by (output started at xxxxx on line 6

What is wrong?

Answer 1

Either header.php or connection.php are outputting some content. You cannot modify the HTTP headers after content is sent, because the headers have already been sent at that point.

A hack of a solution would be this:

<?php

ob_start();

require 'header.php';
require 'connection.php';

mysql_query("DELETE FROM quotes WHERE ID = $_GET[id]") or die("didnt delete properly");

header('Location: index.php');

ob_end_flush();

?>

However, you should instead figure out where content is being sent and suppress it, or reorder it to come after the header() call.

If, as I suspect, header.php outputs an HTML header, you can just eliminate the require 'header.php'; line — the content will never be shown anyway, since this is a redirect.

Also, note that the HTTP standard requires that the value of a Location header be an absolute URL. Therefore, header('Location: index.php'); will generate an HTTP response that is invalid according to the HTTP standard.