PHP中两个日期之间的间隔不是整数

I'm using this to echo interval number of days between two dates, but the second line echoes a float number.

echo (mktime(0,0,0,10,27,2013)-mktime(0,0,0,8,18,2013))/(3600*24).'<br>';
echo (mktime(0,0,0,10,28,2013)-mktime(0,0,0,8,18,2013))/(3600*24).'<br>';

Result:

70
71.041666666667

Can anyone tell me why? Thanks!

Because when dividing in PHP, you'll always receive float.

To get int you have to round it or cast it.

 $int = (int) $float;

or

 $int = round($float, 0);

One exception is when both operands are integers (or strings that can be cast to integers) and they are divisible.

Result: 71.041666666667. Can anyone tell me why? Thanks!

ANSWER: You get that kind of the result because of the DST.

I changed to date.timezone = Asia/Shanghai in php.ini and now am getting integer (correct) result.

Because Asia/Shanghai timezone doesn't use DST. For example try timezone Europe/Berlin (who uses DST), and you will see that you are having the same problem :

date_default_timezone_set('Asia/Shanghai');
echo (mktime(0,0,0,10,28,2013)-mktime(0,0,0,8,18,2013))/(3600*24); # 71

date_default_timezone_set('Europe/Berlin');
echo (mktime(0,0,0,10,28,2013)-mktime(0,0,0,8,18,2013))/(3600*24); # 71.041666666667

^{DST is used [blue] | DST is no longer used [orange] | DST has never been used [red]}

That's why I always suggest to use DateTime instead of mktime(), strtotime() and similar function. DateTime handles leap years and time-zones correctly.

$f = new DateTime('2013-08-18');
$t = new DateTime('2013-10-28');
echo $f->diff($t)->days; # 71

Or one-liner (PHP >= 5.4) :

echo (new DateTime('2013-08-18'))->diff(new DateTime('2013-10-27'))->days; # 71