// 当前时间创建NSDate

    NSDate *myDate = [NSDate date];

    NSLog(@"myDate = %@",myDate);

    //从现在开始的24小时

    NSTimeInterval secondsPerDay = 24*60*60;

    NSDate *tomorrow = [NSDate dateWithTimeIntervalSinceNow:secondsPerDay];

    NSLog(@"myDate = %@",tomorrow);

    //根据已有日期创建日期

     NSTimeInterval secondsPerDay1 = 24*60*60;

    NSDate *now = [NSDate date];

    NSDate *yesterDay = [now addTimeInterval:-secondsPerDay1];

    NSLog(@"yesterDay = %@",yesterDay);

    

    //比较日期

    BOOL sameDate = [now isEqualToDate:yesterDay];

    NSLog(@"sameDate = %lu",sameDate);

    //获取较早的日期

    NSDate *earlierDate = [yesterDay earlierDate:now];

    NSLog(@"earlierDate  = %@",earlierDate);

    //较晚的日期

    NSDate *laterDate = [yesterDay laterDate:now];

    NSLog(@"laterDate  = %@",laterDate);



    //两个日期之间相隔多少秒

    NSTimeInterval secondsBetweenDates= [yesterDay timeIntervalSinceDate:now];

    NSLog(@"secondsBetweenDates=  %lf",secondsBetweenDates);

    //通过NSCALENDAR类来创建日期

    NSDateComponents *comp = [[NSDateComponentsalloc]init];

    [comp setMonth:06];

    [comp setDay:01];

    [comp setYear:2001];

    NSCalendar *myCal = [[NSCalendaralloc]initWithCalendarIdentifier:NSGregorianCalendar];

    NSDate *myDate1 = [myCal dateFromComponents:comp];

    NSLog(@"myDate1 = %@",myDate1);

    

    //从已有日期获取日期

    unsigned units  = NSMonthCalendarUnit|NSDayCalendarUnit|NSYearCalendarUnit;

    NSDateComponents *comp1 = [myCal components:units fromDate:now];

    NSInteger month = [comp1 month];

    NSInteger year = [comp1 year];

    NSInteger day = [comp1 day];

    //NSDateFormatter实现日期的输出

    NSDateFormatter *formatter = [[NSDateFormatteralloc]init];

    [formatter setDateStyle:NSDateFormatterFullStyle];//直接输出的话是机器码

    //或者是手动设置样式[formatter setDateFormat:@"yyyy-mm-dd"];

    NSString *string = [formatter stringFromDate:now];

    NSLog(@"string = %@",string);

    NSLog(@"formater = %@",formatter);