public function check_signup() {

            $this->load->library('form_validation');

            $this->form_validation->set_rules('username','Username','required|min_length[3]|max_length[16]|xss_clean|trim|callback_validate_username');
            $this->form_validation->set_rules('password','Password','required|min_length[6]|xss_clean|callback_validate_signup_passwords');


            return $this->form_validation->run();
        }

        public function validate_username($user) {

            die("validate username called");

            if(!preg_match("/^[a-zA-Z0-9]+$/", $user)) {

                $this->form_validation->set_message('validate_username', '%s must not contain symbols');
                return false;
            }
            return true;
        }