i wanna change url parameters values if has special characters from url. For this i customised filter_uri method in MY_URI core.

class MY_URI extends CI_URI {

function __construct()
{
    parent::__construct();
}


/**
 * Filter URI
 *
 * Filters segments for malicious characters.
 *
 * @param   string  $str
 * @return  void
 */
public function filter_uri(&$str)
{

        if ( ! empty($str) && ! empty($this->_permitted_uri_chars) && ! preg_match('/^['.$this->_permitted_uri_chars.']+$/i'.(UTF8_ENABLED ? 'u' : ''), $str))
        {
         // What i must write here ?
        }
}
}