iOS Working with dates

[idelovski]

What is the best way to store dates that represent just date, not the time.

void  TestDate (void)
{
   NSDateComponents  *comps = [[NSDateComponents alloc] init];
   
   [comps setDay:31];
   [comps setMonth:12];
   [comps setYear:2009];
   
   NSCalendar  *cal = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
   
   NSDate  *dt = [cal dateFromComponents:comps];
   
   [comps release];
   [cal release];
   
   NSDateFormatter  *dfmt = [[NSDateFormatter alloc] init];
   
   [dfmt setDateStyle:kCFDateFormatterShortStyle];
   
   NSString  *dateString = [dfmt stringFromDate:dt];

   [dfmt release];

   NSLog (@"Raw: %@,   Str: %@", dt, dateString);
}

This code gives me this in console - I'm in Central European time zone:

"Raw: 2009-12-30 23:00:00 +0000, Str: 31.12.2009."

Somehow I think this may turn out as a problem. If my app puts this date into a file, then reads it in another time zone it may turn as Dec 30 even in -stringFromDate: and that is not what I want. That is a date of a real paper document and if the document was marked with Dec 31 then that is the date of the document, wherever observer may found himself.

What should I do to store dates that are stable across time zones?

 

[balamw]

Store it as GMT at 00:00:00? (and of course interpret it in GMT).

B

 

[PhoneyDeveloper]

Look at Q&A 1480 and search for en_US_POSIX.

 

[idelovski]

Thanks for the tip, here's the link: Technical Q&A QA1480 - NSDateFormatter and Internet Dates.

 

[North Bronson]

You will have some issues with NSDateComponents in certain circumstances. For example:

In Los Angeles, at 2:00 AM on 7 November 2010, the clocks fell back to 1:00 AM. There were "two different" 1:30 AMs. One wall time gives you two system times. If you generate with NSDateComponents, it is undefined which system time the NSDateComponents correspond to.

For 99 percent of the time, NSDateComponents works perfectly. There are a few corner cases (like daylight savings time) that can make trouble.