//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."\n";