月初の日付のNSDateを作成する

// 月初の日付のNSDateを作成する
NSDate *today = [NSDate date];
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDateComponents *components
= [calendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit|NSWeekdayCalendarUnit
              fromDate:today];
components.day = 1;
NSDate *firstDate = [calendar dateFromComponents:components];

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
formatter.dateFormat  = @"yyyy.MM.dd(E) HH:mm:ss";
NSLog(@"firstDate:%@", [formatter stringFromDate:firstDate]);