PHP: How to send HTTP response code?

If your version of PHP does not include this function:

<?php

function http_response_code($code = NULL) {
        if ($code !== NULL) {
            switch ($code) {
                case 100: $text = 'Continue';
                    break;
                case 101: $text = 'Switching Protocols';
                    break;
                case 200: $text = 'OK';
                    break;
                case 201: $text = 'Created';
                    break;
                case 202: $text = 'Accepted';
                    break;
                case 203: $text = 'Non-Authoritative Information';
                    break;
                case 204: $text = 'No Content';
                    break;
                case 205: $text = 'Reset Content';
                    break;
                case 206: $text = 'Partial Content';
                    break;
                case 300: $text = 'Multiple Choices';
                    break;
                case 301: $text = 'Moved Permanently';
                    break;
                case 302: $text = 'Moved Temporarily';
                    break;
                case 303: $text = 'See Other';
                    break;
                case 304: $text = 'Not Modified';
                    break;
                case 305: $text = 'Use Proxy';
                    break;
                case 400: $text = 'Bad Request';
                    break;
                case 401: $text = 'Unauthorized';
                    break;
                case 402: $text = 'Payment Required';
                    break;
                case 403: $text = 'Forbidden';
                    break;
                case 404: $text = 'Not Found';
                    break;
                case 405: $text = 'Method Not Allowed';
                    break;
                case 406: $text = 'Not Acceptable';
                    break;
                case 407: $text = 'Proxy Authentication Required';
                    break;
                case 408: $text = 'Request Time-out';
                    break;
                case 409: $text = 'Conflict';
                    break;
                case 410: $text = 'Gone';
                    break;
                case 411: $text = 'Length Required';
                    break;
                case 412: $text = 'Precondition Failed';
                    break;
                case 413: $text = 'Request Entity Too Large';
                    break;
                case 414: $text = 'Request-URI Too Large';
                    break;
                case 415: $text = 'Unsupported Media Type';
                    break;
                case 500: $text = 'Internal Server Error';
                    break;
                case 501: $text = 'Not Implemented';
                    break;
                case 502: $text = 'Bad Gateway';
                    break;
                case 503: $text = 'Service Unavailable';
                    break;
                case 504: $text = 'Gateway Time-out';
                    break;
                case 505: $text = 'HTTP Version not supported';
                    break;
                default:
                    exit('Unknown http status code "' . htmlentities($code) . '"');
                    break;
            }
            $protocol = (isset($_SERVER['SERVER_PROTOCOL']) ? $_SERVER['SERVER_PROTOCOL'] : 'HTTP/1.0');
            header($protocol . ' ' . $code . ' ' . $text);
            $GLOBALS['http_response_code'] = $code;
        } else {
            $code = (isset($GLOBALS['http_response_code']) ? $GLOBALS['http_response_code'] : 200);
        }
        return $code;
    }