How to clear NSDate milliseconds
I want to keep date/times in a CoreData store with no seconds or milliseconds. (I'm doing some processing to round times off, and stray seconds/milliseconds become a monkey wrench.) It's easy enough to drop the seconds:
NSDate *now = [NSDate date];
NSDateComponents *time = [[NSCalendar currentCalendar]
components:NSHourCalendarUnit | NSMinuteCalendarUnit
| NSSecondCa开发者_Python百科lendarUnit fromDate:now];
NSDate *nowMinus = [now addTimeInterval:-time.second];
// e.g. 29 Aug 10 4:43:05 -> 29 Aug 10 4:43:00
This works great to zero out the seconds, but I can't find an NSMillisecondCalendarUnit I could use to zero out the milliseconds, and I need to. Any ideas? Thanks.
timeIntervalSince1970
returns the number of seconds (in a double) since January the 1st, 1970. You can use this time to truncate any amount of seconds you like. To round down to the nearest minute, you could do:
NSTimeInterval timeSince1970 = [[NSDate date] timeIntervalSince1970];
timeSince1970 -= fmod(timeSince1970, 60); // subtract away any extra seconds
NSDate *nowMinus = [NSDate dateWithTimeIntervalSince1970:timeSince1970];
Floating point data types are inherently imprecise, but the above may be precise enough for your needs.
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