NSDateComponents issue - incorrect day

Question

I have a NSDateComponents problem. I have two NSDates that I am trying to compare by checking if their year, month and day match. This I am doing by converting the NSDate values to these integer components as follows:

//NSDate *cgiDate is previously set to 2011-08-04 00:00:00 +0000 
//NSDate *orderDate is previously set to 2011-08-04 14:49:02 +0000
NSCalendar *calendar = [NSCalendar currentCalendar];
NSDateComponents *cgiDateComponents = [calendar components:( NSYearCalendarUnit | NSMonthCalendarUnit |  NSDayCalendarUnit ) fromDate:cgiDate];
NSCalendar *orderCalendar = [NSCalendar currentCalendar];
NSDateComponents *orderDateComponents = [orderCalendar components:( NSYearCalendarUnit | NSMonthCalendarUnit |  NSDayCalendarUnit ) fromDate:orderDate];
if (([cgiDateComponents day] == [orderDateComponents day]) &&
    ([cgiDateComponents month] == [orderDateComponents month]) &&
    ([cgiDateComponents year] == [orderDateComponents year])) {
       GHTestLog(@"MATCHED");
 } else {
       GHTestLog(@"Not matched");
       GHTestLog(@"Day: %d vs. %d", [cgiDateComponents day], [orderDateComponents day]);
 }

My result is Not Matched, Day: 3 vs. 4. Why would this be?

I have read with great interest the following questions: NSDateComponents - day method returning wrong day and https://stackoverflow.com/questions/3920445/nsdatecomponents-incorrectly-reporting-day however neither answer my question of why this is not working.

Any advice?

Answer 1

I think the issue is the following: Your dates are set in GMT time zone (+0000) If you are in the US, for example at GTM-6, then by the -currentCalendar the first date will be 6pm on Aug 3rd while second date will be 8:49am on Aug 4th.

You should force your calendar to have the UTC (GMT) timezone, or put the dates in your time zone, depending what is correct for your application.