PHP date calculation

Question

What is the best (date format independent way) in PHP to calculate difference in days between two dates in specified format.

I tried the following function:

Answer 1

The problem with PHP is that it doesn't have a definite DateTime type. You can use a Unix timestamp, or the built-in DateTime class, but they are pretty limited in their functionality. I expect that there should be some 3rd party classes with more extensive support for date-time calculations, but I haven't looked for it.

Using Unix timestamps for date (not time) calculations is also tricky. You'd have to discard the time part, but simply resetting to 00:00 is not safe because of daylight savings time (DST). DST has the effect that there are two days every year that don't have exactly 24 hours. Thus, when adding/subtracting dates you might end up with a value that does not divide evenly with 3600*24.

I'd suggest looking for some 3rd party class that has proper support for all this stuff. Date/Time calculations are awesome in their ugliness. :P