曾经做过类似的，是这样计算的。原是代码不是下面的，下面的是经过改动的
<?
function calculate_days($from,$to)
{
for($days=strtotime($from);$days<=strtotime($to);$days+=3600*24)
{
$day[]=date("Y-m-d",$days);
}
return $day;
}
$from1="2011-10-9";
$to1="2011-11-4";
$from2="2011-10-23";
$to2="2012-3-22";
print_r(array_intersect(calculate_days($from1,$to1),calculate_days($from2,$to2)));
/*
Array
(
[14] => 2011-10-23
[15] => 2011-10-24
[16] => 2011-10-25
[17] => 2011-10-26
[18] => 2011-10-27
[19] => 2011-10-28
[20] => 2011-10-29
[21] => 2011-10-30
[22] => 2011-10-31
[23] => 2011-11-01
[24] => 2011-11-02
[25] => 2011-11-03
[26] => 2011-11-04
)
*/
?>
