Custom validation rule in CodeIgniter

gistfile1.txt

<?php

class Something extends CI_Controller {

  # some code

  /**
  * Full Name Check, custom validation rule
  * How to use? : $this->form_validation->set_rules('fullName', 'Full Name', 'required|callback_fullname_check');
  */
  public function fullname_check($str) {
    if (! preg_match("/^([a-z0-9 ])+$/i", $str)) {
        $this->form_validation->set_message('fullname_check', 'The %s field can only be alpha numeric');
        return FALSE;
    } else {
        return TRUE;
    }
  }
}