php函数-计算两个日期相差多少天

<?PHP 

/*
*
*函数功能：计算两个以YYYY-MM-DD为格式的日期，相差几天
*
*/
function getChaBetweenTwoDate($date1,$date2){

    $Date_List_a1=explode("-",$date1);
    $Date_List_a2=explode("-",$date2); 

    $d1=mktime(0,0,0,$Date_List_a1[1],$Date_List_a1[2],$Date_List_a1[0]); 

    $d2=mktime(0,0,0,$Date_List_a2[1],$Date_List_a2[2],$Date_List_a2[0]); 

    $Days=round(($d1-$d2)/3600/24); 

    return $Days;
}

echo getChaBetweenTwoDate('2010-08-11','2010-08-16');
echo "<br>";
echo getChaBetweenTwoDate('2010-08-16','2010-08-11');
?>