Form validation: Callback not changing the input value

[eluser]Nis Sarup[/eluser]
Here is the callback:

Code:

function _validate_birthday()
        {
            // Validates the birthdate from the user input.
            $day     = (int)$this->input->post('birthday');
            $month    = (int)$this->input->post('birthday_month');
            $year    = (int)$this->input->post('birthday_year');
            
            if (0 > $day || $day > 32) {
                $this->validation->set_message('validate_birthday', 'Invalid day in birthdate.');
                return false;
            }
            
            if (0 > $month || $month > 13) {
                $this->validation->set_message('validate_birthday', 'Invalid month in birthdate.');
                return false;
            }
            
            if (0 > $day || $day > (int)date('Y')) {
                $this->validation->set_message('validate_birthday', 'Invalid year in birthdate.');
                return false;
            }
            
            $birthday = mktime(0, 0, 0, $month, $day, $year);
            
            if ($birthday > strtotime('-18 years')) {
                $this->validation->set_message('validate_birthday', 'You must be 18 years old to sign up.');
                return false;
            }
            
            return $birthday;
        }

It looks at the 3 inputs for the birthday, makes the timestamp and returns it if everything is allright.