计算2000年01月01日起到指定日的天数

这是一个计算2000年01月01日起到指定日的天数的函数
 
(算头也算尾)日期格式为：YYYY-MM-DD
 

<?php
// 计算从2000年01月01日开始到某日的天数

function cal_start2end($end_day,$start_day)
{

$start_day=ereg_replace("-","",$start_day);
$end_day=ereg_replace("-","",$end_day);

if($end_day>=$start_day)
{ // 截止日期大于开始日期
 if(substr($end_day,0,4)==substr($start_day,0,4))
 {

if( is_int(substr($end_day,0,4)/4) )
 $leap_day=29; //leap year
else
 $leap_day=28;

// //同一年

 if(substr($end_day,4,2)==substr($start_day,4,2))
 {
// the same month
 $endday_from_startday=$end_day-$start_day+1;

 }
 else
 {
// not same month

 switch (substr($end_day,4,2))
 {
 case "01":
 $endday_from_newyear=substr($end_day,6,2)+1;
 break;
 case "02":
 $endday_from_newyear=substr($end_day,6,2)+31;
 break;
 case "03":
 $endday_from_newyear=substr($end_day,6,2)+$leap_day+31;
 break;
 case "04":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*2;
 break;
 case "05":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*2+30;
 break;
 case "06":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*3+30;
 break;
 case "07":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*2+30*2;
 break;
 case "08":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*3+30*2;
 break;
 case "09":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*5+30*2;
 break;
 case "10":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*5+30*3;
 break;
 case "11":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*5+30*4;
 break;
 case "12":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*5+30*5;
 break;
 }
 $endday_from_startday=$endday_from_newyear;
 }

return ($endday_from_startday);

 }
 else
 {
// 不同年！

$differ_year=substr($end_day,0,4)-substr($start_day,0,4);

$how_int_4_floor=floor($differ_year/4)+1; // 向下取整
$how_int_4_ceil=ceil($differ_year/4)+1; // 向上取整

if($how_int_4_floor==$how_int_4_ceil)
 $how_leap_year=$how_int_4_floor-1;
else
 $how_leap_year=$how_int_4_floor;

$how_noleap_year=$differ_year-$how_leap_year;

$differ_year2day=$how_noleap_year*365+$how_leap_year*366;

if( is_int(substr($end_day,0,4)/4) )
 $leap_day=29; //leap year
else
 $leap_day=28;

 if(substr($end_day,4,2)==substr($start_day,4,2))
 {
// the same month
 $endday_from_startday=$differ_year2day+ substr($end_day,4,2);

 }
 else
 {
// not same month

 switch (substr($end_day,4,2))
 {
 case "01":
 $endday_from_newyear=substr($end_day,6,2)+1;
 break;
 case "02":
 $endday_from_newyear=substr($end_day,6,2)+1+31;
 break;
 case "03":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31;
 break;
 case "04":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*2;
 break;
 case "05":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*2+30;
 break;
 case "06":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*3+30;
 break;
 case "07":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*2+30*2;
 break;
 case "08":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*3+30*2;
 break;
 case "09":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*5+30*2;
 break;
 case "10":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*5+30*3;
 break;
 case "11":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*5+30*4;
 break;
 case "12":
 $endday_from_newyear=substr($end_day,6,2)+1+$leap_day+31*5+30*5;
 break;
 } //End of switch

 $endday_from_startday=$endday_from_newyear+$differ_year2day;
 } //End of not same month

return ($endday_from_startday);

 } //End of year
} //End of $end_day>=$start_day

} //End of function

$start_day="2000-01-01";

$end_day="2011-01-01";

echo "您输入的是：".$end_day." \n";
$endday_from_startday=cal_start2end($end_day,$start_day);

echo "该日距离$start_day 共 ".$endday_from_startday." 天";

?>
 时间太少了，那位大虾可以修改为计算任意两日期之间的间隔最好！！！！！