NSDateから時刻０時のNSDateを作成する

// 時刻０時のNSDateを作成
NSDate *today = [NSDate date];
NSCalendar *calendar = [NSCalendar currentCalendar];
NSDateComponents *components
= [calendar components:NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit
              fromDate:today];
NSDate *date = [calendar dateFromComponents:components];

// ログ出力
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
formatter.dateFormat = @"yyyy.MM.dd HH:mm:ss";
NSLog(@"today:%@ date:%@", [formatter stringFromDate:today], [formatter stringFromDate:date]);