PHP DateTime()

[Jeff Mott]

I see your point, so my basis is flawed to. PHP is currently subtracting the number of days in the preceding month, thus the March 31st minus a month is March 2nd, which is still wrong... So obviously it is a bit more complex than that too.

This is why I agree with .NET:

var march = new DateTime(2012, 03, 31);
var may = new DateTime(2012, 05, 31);
Console.WriteLine(may.ToString("yyyy-MM-dd"));
var april = may.AddMonths(-1);
Console.WriteLine(april.ToString("yyyy-MM-dd"));
 
var march = new DateTime(2012, 03, 31);
Console.WriteLine(march.ToString("yyyy-MM-dd"));
var february = march.AddMonths(-1);
Console.WriteLine(february.ToString("yyyy-MM-dd"));
var january = february.AddMonths(-1);
Console.WriteLine(january.ToString("yyyy-MM-dd"));
Console.ReadKey();
/*
  Output:
  2012-05-31
  2012-04-30
  2012-03-31
  2012-02-29
  2012-01-29 // this one irks me a bit, but it is understandable.
*/

I have to give it to the MS folks, they really made it nice and maybe I just expect other languages to do it as well.

It's a little interesting because, based on results you've posted, .NET behavior will match common sense but break mathematics. For example:

2012-03-31 -1 month returns 2012-02-29, and 2012-02-29 +1 month returns 2012-03-29. In other words, x + 1 -1 != x.

[cpradio]

It's a little interesting because, based on results you've posted, .NET behavior will match common sense but break mathematics. For example:

2012-03-31 -1 month returns 2012-02-29, and 2012-02-29 +1 month returns 2012-03-29. In other words, x + 1 -1 != x.

Yeah, I know. I had to run it three times to verify I didn't flub it up with some stupid mistake, but it does indeed do that. *sigh*, not as infallible as I was led to believe, but, I do appreciate the fact that like PHP, it does give you tools to get better validity when you need it (such as getting the last day in a given month consistently).

[StarLion]

Off Topic:

Stupid calendar makers.

[K. Wolfe]

Off Topic:

Stupid calendar makers.

Fer realz.

What I'm doing is running a daily batch of usage per billing cycle. A customer's billing cycle can land on any day (1-31). Daily I need to calculate their usage for their bill cycle. So today, the 25th, I'd be calculating for everyone whos bill cycle is on the 25th (Jan - Dec). On the 28th, I will run 4 seperate batches for the 28th, 29th, 30th and 31st to handle months that do not have certain days. This is why I need to be able to run on fictional dates..

I'm going to use literal strings in this function to avoid any unwanted side effects, and handle the year by hand. I'll post the code when I have completed.

[K. Wolfe]

Ugly but whatever:

//bill cycle date to run for
$day = 25;
$month = 1;
$year = 2013;
if($month == 1) {
    $startDate = ($year-1) . '-12-' . $day;
    $endDate = $year . '-' . $month . '-' . $day;
} else {
    $startDate = $year . '-' . ($month-1) . '-' . $day;
    $endDate = $year . '-' . $month . '-' . $day;
}