선언은
NSCalendar *calendar = [NSCalendar currentCalendar];
unsigned int unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
NSDateComponents *c = [calendar components:unitFlags fromDate:[NSDate date]];
나중에 release하는 것을 잊지말자
[c year]
[c month]
[c day]
[c hour]
[c minute]
[c second]
