I want to create a NSDateFormatter that should 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, the anotherDateString is 2014-05-13 23:31:41.374000. Why does it truncate the milliseconds?
It seems that NSDateFormatter works only with millisecond resolution, for the
following reasons:
By setting a breakpoint in CFDateFormatterCreateDateFromString, one can
see that this function is called 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 from
CFDateFormatter.c
which is open source. One can see that all calendrical calculations are made using the
ICU Calendar Classes.
It is stated in calendar.h that Calendar uses UDate which has a millisecond resolution:
/**
* <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.)
* ...