private function formatH(&$str) {
    if (strstr($str, '%H'))
      $str = str_replace('%H', sprintf('%02d', $this->hour), $str);
  }
private function formatH(&$str) {
    if (strstr($str, '%H'))
      $str = str_replace('%H', sprintf('%02d', $this->hour), $str);
  }
24-hour format of an hour with leading zeros
@param type $str