即使在放入ob_start（）之后，头函数也不起作用; [重复]

Question

Possible Duplicate:
Headers already sent by PHP

I have the following code in my php file. I want to redirect from this page using header function which is clear in code below. I have made sure that there are no echo commands and have also placed ob_start(); at the beginning of the file yet i am getting the following error:

Warning: Cannot modify header information - headers already sent by (output started at /hermes/bosweb/web054/b548/ipg.psdingcampsduscom/facebook_registration_plugin/store_user_data.php:1) in /hermes/bosweb/web054/b548/ipg.psdingcampsduscom/facebook_registration_plugin/store_user_data.php on line 171

here is the code :

<?php ob_start();
            define('FACEBOOK_APP_ID', 'xxxxxxxx');
            define('FACEBOOK_SECRET', 'xxxxxxxxxx');
            // No need to change function body
            function parse_signed_request($signed_request, $secret) {
                list($encoded_sig, $payload) = explode('.', $signed_request, 2);
                // decode the data
                $sig = base64_url_decode($encoded_sig);
                $data = json_decode(base64_url_decode($payload), true);
                if (strtoupper($data['algorithm']) !== 'HMAC-SHA256') {
                    error_log('Unknown algorithm. Expected HMAC-SHA256');
                    return null;
                }
                // check sig
                $expected_sig = hash_hmac('sha256', $payload, $secret, $raw = true);
                if ($sig !== $expected_sig) {
                    error_log('Bad Signed JSON signature!');
                    return null;
                }
                return $data;
            }
            function base64_url_decode($input) {
                return base64_decode(strtr($input, '-_', '+/'));
            }
            if ($_REQUEST) {
                $response = parse_signed_request($_REQUEST['signed_request'],
                                FACEBOOK_SECRET);
header("location: fbwe/step2.php?name=".$name."&email=".$email."&gender=".$gender."&arts=".$cb1."&act=".$cb2."&cooking=".$cb3."&dance=".$cb4."&designing=".$cb5."&fashion=".$cb6."&interior=".$cb7."&modeling=".$cb8."&photography=".$cb9."&poetry=".$cb10."&programming=".$cb11."&reading=".$cb12."&sketching=".$cb13."&singing=".$cb14."&sports=".$cb15."&stunting=".$cb16."&videography=".$cb17."&other=".$cb18);

                // Connecting to Database

            } else {
                //echo '$_REQUEST is empty';
            }
            ?>

Can anyone figure out what is wrong?

Answer 1

Few things that should be keep in mind before using header function.

1. There should be no echo or print statement before the header function.
2. There should be no space on top and bottom of the page i.e page should start with <?php and end with ?>. There must be no blank space after or before these tags.