how to show message after logout in codeigniter

1 function logout_with_flashdata(){
2    $ci =& get_instance();
3    foreach($ci->session->userdata as $k => $v){
4      if($k == 'message' || $k == '__ci_vars'){
5        continue;
6      }
7      $ci->session->unset_userdata($k);
8    }
9  }
10