objective c - Get the Week Number in iOS SDK -

i want week number of year date.i tried code follow gives me wrong week number.

my code week number:

nsdateformatter *dateformatter = [[nsdateformatter alloc] init];     [dateformatter setdateformat:@"yyyy-mm-dd"];     nsdate *date = [dateformatter datefromstring:@"2012-09-15"];       nscalendar *calendar = [nscalendar currentcalendar];      nslog(@"week: %i", [[calendar components: nsweekofyearcalendarunit fromdate:date] weekofyear]); //display 38 instead of 37 } 

note: if try with [nsdate date] display correct.

help me solve this.. thank you,

objectivec:

 nscalendar *calendar = [nscalendar currentcalendar];  nsdatecomponents *datecomponent = [calendar components:(nsweekofyearcalendarunit | nsdaycalendarunit | nsmonthcalendarunit | nsyearcalendarunit) fromdate:[nsdate date]];  nslog(@"%@",datecomponent); 

swift:

let calendar = nscalendar.currentcalendar() let datecomponent = calendar.components([.weekofyear, .day, .month, .year], fromdate: nsdate(timeintervalsincenow: 0)) print("weekofyear \(datecomponent.weekofyear)") 

swift 3:

let component = calendar.current.component(.weekofyear, from: date()) print("week of year \(component)")