ขอถามเกี่ยวกับ function DateThai กับการ export ครับ

 <?php
	function DateThai($strDate)
	{
		$strYear = date("Y",strtotime($strDate))+543;
		$strMonth= date("n",strtotime($strDate));
		$strDay= date("j",strtotime($strDate));
		$strHour= date("H",strtotime($strDate));
		$strMinute= date("i",strtotime($strDate));
		$strSeconds= date("s",strtotime($strDate));
		$strMonthCut = Array("","ม.ก.", "ก.พ.", "ม.ค.", "เม.ย.", "พ.ค.", "มิ.ย.", "ก.ค.", "ส.ค.", "ก.ย.", "ต.ค.", "พ.ย.", "ธ.ค.");
		$strMonthThai=$strMonthCut[$strMonth];
		return "$strDay $strMonthThai $strYear";
	}



	?>

<?
header("Content-Type: application/x-msexcel"); 
header("content-disposition: attachment;filename=Data_bill.xls");
echo "<meta http-equiv='Content-Type' content='text/html; charset=windows-874'>";
?>

  <td bgcolor="#FFFFFF" ><?
		  DateThai($strDate2 );
$strDate2 = ($objResult["beforerank"]);
if($strDate2 == "0000-00-00")
{
echo $strDate2 = "";
}
else
{
echo   DateThai($strDate2 );
}	    ?></td>