//在PHP中处理日期非常不方便，比如求两个日期之间相差的月份？该怎么办呢？
//文件名：date.inc.php3
//在使用这两个函数前，要先将日期或日期时间转换成timestamp类型。
//如：
//$today=mktime（0,0,0,date（"m"）,date（"d"）,date（"Y"））;
function dateadd（$part,$n,$datetime）{
$year=date（"Y",$datetime）;
$month=date（"m",$datetime）;
$day=date（"d",$datetime）;
$hour=date（"H",$datetime）;
$min=date（"i",$datetime）;
$sec=date（"s",$datetime）;
$part=strtolower（$part）;
$ret=0;
switch （$part） {
case "year":
$year+=$n;
break;
case "month":
$month+=$n;
break;
case "day":
$day+=$n;
break;
case "hour":
$hour+=$n;
break;
case "min":
$min+=$n;
break;
case "sec":
$sec+=$n;
break;
default:
return $ret;
break;
}
$ret=mktime（$hour,$min,$sec,$month,$day,$year）;
return $ret;
}
function datediff（$part,$date1,$date2）{
//$diff=$date2-$date1;
$year1=date（"Y",$date1）;
$year2=date（"Y",$date2）;
$month2=date（"m",$date2）;
$month1=date（"m",$date1）;
$day2=date（"d",$date2）;
$day1=date（"d",$date1）;
$hour2=date（"d",$date2）;
$hour1=date（"d",$date1）;
$min2=date（"i",$date2）;
$min1=date（"i",$date1）;
$sec2=date（"s",$date2）;
$sec1=date（"s",$date1）;
$part=strtolower（$part）;
$ret=0;
switch （$part） {
case "year":
$ret=$year2-$year1;
break;
case "month":
$ret=（$year2-$year1）*12+$month2-$month1;
break;
case "day":
$ret=（mktime（0,0,0,$month2,$day2,$year2）-mktime（0,0,0,$month1,$day1,$year1））/（3600*24）;
break;
case "hour":
$ret=（mktime（$hour2,0,0,$month2,$day2,$year2）-mktime（$hour1,0,0,$month1,$day1,$year1））/3600;
break;
case "min":
$ret=（mktime（$hour2,$min2,0,$month2,$day2,$year2）-mktime（$hour1,$min1,0,$month1,$day1,$year1））/60;
break;
case "sec":
$ret=$date2-$date1;
break;
default:
return $ret;
break;
}
return $ret;
}
}
