NSDateFormater - returns same year for 2015 and 2016 date [duplicate]

Question

I have found a strange behaviour in NSDateFormatter with LLLL YYYY format, where it returns year 2015 for both 2015-01-01 and 2016-01-01 dates.

Am I missing something or is it a bug in the formatter class?

Code to reproduce:

NSDateFormatter *formatter = [NSDateFormatter new];
formatter.dateFormat = @"LLLL YYYY";

NSDate *d1 = [NSDate dateWithTimeIntervalSince1970:1420070400]; // 2015-01-01T00:00:00Z
NSDate *d2 = [NSDate dateWithTimeIntervalSince1970:1451606400]; // 2016-01-01T00:00:00Z

NSLog(@"%@ => %@", d1, [formatter stringFromDate:d1]); // 2015-01-01 00:00:00 +0000 => January 2015
NSLog(@"%@ => %@", d2, [formatter stringFromDate:d2]); // 2016-01-01 00:00:00 +0000 => January 2015

Both cases print "January 2015", but I would expect "January 2016" in the second case.

Answer 1

You should use yyyy instead of YYYY, because YYYY is something different...

A deeper explanation from the docs:

A common mistake is to use YYYY. yyyy specifies the calendar year whereas YYYY specifies the year (of “Week of Year”), used in the ISO year-week calendar. In most cases, yyyy and YYYY yield the same number, however they may be different. Typically you should use the calendar year.

Answer 2

You should use yyyy, not YYYY.