class MY_Controller extends CI_Controller
{
    public function __construct()
    {
        parent::__construct();
        /*判斷是否登錄，判斷當(dāng)前URL是否是auth/login*/
        if ( ! $this->tank_auth->is_logged_in()
                && ( $this->router->fetch_class() != 'auth' && $this->router->fetch_method() != 'login'))
        {
            $redirect = $this->uri->uri_string();

            if ( $_SERVER['QUERY_STRING'])
            {
                $redirect .= '?' . $_SERVER['QUERY_STRING'];
            }
            /*跳轉(zhuǎn)到用戶登陸頁面，指定Login后跳轉(zhuǎn)的URL*/
            redirect('auth/login?redirect='.$redirect);
        }   
    }
}

class User extends MY_Controller
{
    function login()
    {

        if ($this->tank_auth->is_logged_in()) {                                    // logged in
            redirect('/');

        } else {
            //other codes here......
            /*判斷是否有redirect信息*/
            $data['redirect'] = isset($_GET['redirect']) ? $_GET['redirect'] : '/';

            if ($this->form_validation->run()) {                                // validation ok
                if ($this->tank_auth->login(
                        $this->form_validation->set_value('login'),
                        $this->form_validation->set_value('password'),
                        $this->form_validation->set_value('remember'),
                        $data['login_by_username'],
                        $data['login_by_email'])) {                                // success
                    redirect($data['redirect']);

                } else {
                    //error handling
                }
            }
            $this->load->view("login_form")
        }
    }
/*
Note: 在login_form中需要注意，提交表單的form地址：
<?php echo form_open(site_url("/auth/login?redirect=".$redirect)); ?>
*/
}

<?php echo form_open(site_url("/auth/login?redirect=".$redirect)); ?>