ios 获取当前系统时间

1. NSDate + NSDateFormatter

    NSDate *date = [NSDate date];

    NSDateFormatter *format = [[NSDateFormatter alloc] init];

    [format setDateFormat:@"YYYY/MM/dd hh:mm:ss.SSSSSSSS"];

    NSString *sDate = [format stringFromDate:date];

    NSLog(@"%@",sDate);

执行结果：精确到1ms

2015-03-30 21:35:13.799 My Legend[1037:53843] 2015/03/30 09:35:13.79900000

2.NSDate + NSCalendar + NSDateComponents

    NSDate *now = [NSDate date];

    NSLog(@"now date is: %@", now);

    NSCalendar *calendar = [NSCalendar currentCalendar];

    NSUInteger unitFlags = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond |NSCalendarUnitNanosecond;

    NSDateComponents *dateComponent = [calendar components:unitFlags fromDate:now];

    NSLog(@"%ld/%ld/%ld %ld:%ld:%ld.%ld",(long)dateComponent.year, (long)dateComponent.month, (long)dateComponent.minute, (long)dateComponent.hour, (long)dateComponent.minute, (long)dateComponent.second, (long)dateComponent.nanosecond);

执行结果：精确到1ns

2015-03-30 21:35:13.800 My Legend[1037:53843] now date is: 2015-03-30 13:35:13 +0000

2015-03-30 21:35:13.800 My Legend[1037:53843] 2015/3/35 21:35:13.800027012

3.C标准库函数 time

time_t 类型是用来存储从1970年到现在经过了多少秒

        time_t tBuf;

        tBuf=time(NULL);

        NSLog(@"%s", ctime(&tBuf));

        NSString *date = [NSString stringWithCString:ctime(&tBuf) encoding:NSUTF8StringEncoding];

        NSLog(@"%@\n", date);

执行结果 精确到1s

Sun Aug  2 11:42:01 2015

Sun Aug  2 11:42:01 2015

注： 可以用tm提取time时间信息

struct tm {//tm结构

	int	tm_sec;		/* seconds after the minute [0-60] */

	int	tm_min;		/* minutes after the hour [0-59] */

	int	tm_hour;	/* hours since midnight [0-23] */

	int	tm_mday;	/* day of the month [1-31] */

	int	tm_mon;		/* months since January [0-11] */

	int	tm_year;	/* years since 1900 */

	int	tm_wday;	/* days since Sunday [0-6] */

	int	tm_yday;	/* days since January 1 [0-365] */

	int	tm_isdst;	/* Daylight Savings Time flag */

	long	tm_gmtoff;	/* offset from CUT in seconds */

	char	*tm_zone;	/* timezone abbreviation */

};

        //提取从time获取的 time_t类型 时间信息

        struct tm tmBuf;

        tmBuf=*localtime(&tBuf);

        NSLog(@"%d:%d:%d", tmBuf.tm_hour, tmBuf.tm_min,tmBuf.tm_sec);

执行结果

11:57:27