判断是否是当前日期,是哪里出问题了呢?

controllerComps:视图控制器的NSDateComponents指针;
nowComs:当前日期的NSDateComponents指针

BOOL isToday = ((controllerComps.year == nowComps.year)&&(controllerComps.month == nowComps.month)&&(controllerComps.date == nowComps.date));    
NSLog(@"isToday:%hhd",isToday);

以下为打印内容:
2015-03-19 14:59:58.267 Playing-higherExercise[6423:1141331] nowComps:
Calendar Year: 2015
Month: 3
Leap month: no
Day: 19
2015-03-19 14:59:58.268 Playing-higherExercise[6423:1141331] controllerComps:
Calendar Year: 2015
Month: 3
Leap month: no
Day: 18
2015-03-19 14:59:58.269 Playing-higherExercise[6423:1141331] isToday:1
//这两个日期不是不一样的吗?为什么结果为真呢?