$url = (isHTTPS() ? 'https://' : 'http://') . $_SERVER['HTTP_HOST']; //获取域名
//判断是否是HTTPS
function isHTTPS()
{
    if (defined('HTTPS') && HTTPS) return true;
    if (!isset($_SERVER)) return FALSE;
    if (!isset($_SERVER['HTTPS'])) return FALSE;
    if ($_SERVER['HTTPS'] === 1) {  //Apache
        return TRUE;
    } elseif ($_SERVER['HTTPS'] === 'on') { //IIS
        return TRUE;
    } elseif ($_SERVER['SERVER_PORT'] == 443) { //其他
        return TRUE;
    }
    return FALSE;
}