tp5 计算两个日期之间相差的天数

//两个日期之间相差的天数
    function diffBetweenTwoDays ($day1, $day2)
    {
        $second1 = strtotime($day1);
        $second2 = strtotime($day2);

        if ($second1 < $second2) {
            $tmp = $second2;
            $second2 = $second1;
            $second1 = $tmp;
        }
        return ($second1 - $second2) / 86400;
    }

$day1 = "2013-07-27";
$day2 = "2013-08-04";
$diff = diffBetweenTwoDays($day1, $day2);
echo $diff."
";