NSDateFormatter error in milliseconds

Question

I want to create an NSDateFormatter that needs to parse dates like this "2014-05-13 23: 31: 41.374577". So:

NSDateFormatter *formatter = [[NSDateFormatter alloc] init]; formatter.dateFormat = @"yyyy-MM-dd HH:mm:ss.SSSSSS"; NSString *dateString = @"2014-05-13 23:31:41.374577"; NSDate *date = [formatter dateFromString:dateString]; NSString *anotherDateString = [formatter stringFromDate:date]; 

However, anotherDateString is 2014-05-13 23:31:41.374000 . Why does it truncate milliseconds?

Answer 1

It seems that NSDateFormatter only works with millisecond resolution, for the following reasons:

• By setting a breakpoint in CFDateFormatterCreateDateFromString , you can call this function from dateFromString: ::

   (lldb) bt * thread #1: tid = 0x26d03f, 0x018f47d0 CoreFoundation`CFDateFormatterCreateDateFromString, queue = 'com.apple.main-thread', stop reason = breakpoint 3.1 frame #0: 0x018f47d0 CoreFoundation`CFDateFormatterCreateDateFromString frame #1: 0x0116e0ea Foundation`getObjectValue + 248 frame #2: 0x0116dfc7 Foundation`-[NSDateFormatter getObjectValue:forString:errorDescription:] + 206 frame #3: 0x0116879f Foundation`-[NSDateFormatter dateFromString:] + 71 * frame #4: 0x00002d56 foo`main(argc=1, argv=0xbfffee54) + 182 at main.mm:25 

• CFDateFormatterCreateDateFromString() is CFDateFormatter.c which is open source. You can see that all calendar calculations are done using ICU calendar classes .

• Calendar states that Calendar uses UDate , which has a resolution in milliseconds:

   /** * <code>Calendar</code> is an abstract base class for converting between * a <code>UDate</code> object and a set of integer fields such as * <code>YEAR</code>, <code>MONTH</code>, <code>DAY</code>, <code>HOUR</code>, * and so on. (A <code>UDate</code> object represents a specific instant in * time with millisecond precision. See UDate * for information about the <code>UDate</code> class.) * ...