php使用datetime类做时间日期到字符串转换
javascript中date和string的互转
若要使用php来比较日期，最好用datetime::diff
但是这个是5.3才支持的，如果没有这样的环境，可以使用来比较
如下例子，会输出right
$date1=strtotime('2009-8-9 20:00');
$date2=strtotime('2009-9-9 1:00');
if($date1echo 'right';
else
echo 'wrong';
注：datetime::diff
datetime::diff(php 5 >= 5.3.0)
datetime::diff — returns the difference between two datetime objects
descriptionpublic dateinterval datetime::diff ( datetime $datetime [, bool $absolute ] )
returns the difference between two datetime objects.
parametersdatetimethe date to compare to.
absolutewhether to return absolute difference. defaults to false.
return valuesthe difference between two dates.