function get_active_user(){
    $t = &get_instance();
    $user = $t->session->userdata("user");
    if($user)
    return $user;
    else
    return false;
  }

class Dashboard extends CI_Controller{
    function __construct()
    {
        parent::__construct();
        $this->load->model('Site_user_model');
   if(!get_active_user()){
      redirect(base_url("login"));
    }