Question

 NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
 [dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];
 [dateFormatter setDateFormat:@"yyyy-MM-dd"];
 NSDate *date1 = [dateFormatter dateFromString:@"1213-02-27"];
 NSTimeInterval nsdateResult = [date1 timeIntervalSince1970];
 NSTimeInterval sqliteResult = -23883638400;
 GHAssertEquals(sqliteResult, nsdateResult, @"sqlite and nsdate should agree");

The expected number is what SQLite tells me should be the result, but this test fails since Cocoa tells me -23883033600 instead of -23883638400…i.e. 4 days later!
What gives? Am I doing something wrong or is either SQLite or Cocoa wrong?

Edit

Just checked the math and it seems Cocoa is giving me a wrong value: according to Wolfram Alpha, there are 276431 days between 2/27/1213 and 1/1/1970. Take this times 24*60*60, and you get the value given by SQLite… so am I doing something wrong or is this some kind of Cocoa bug?

Edit 2
Fvu is right, it has to do with the Gregorian/Julian craziness back in 1582.

NSDate *date1 = [dateFormatter dateFromString:@"1582-10-15"];
NSDate *date2 = [dateFormatter dateFromString:@"1582-10-14"];
NSTimeInterval i = [date2 timeIntervalSinceDate:date1];

Surprisingly, i is 777600, i.e. 10/14 is 9 days LATER than 10/15 because it automatically is viewed as a Julian date whereas 10/15 is viewed as a Gregorian date. So basically what I will need to do is convert any dates before 10/15 from the Julian to the Gregorian calendar.

Answer 1

Your sample date predates the Gregorian calendar so I think some oddities can be expected. However, as at the introduction of the Gregorian calendar the date advanced by 10 days I don’t have a bulletproof explanation for the calculated 4 day difference.