如何计算从今天开始以来的秒数？

Question

我想得到午夜以来的秒数.

这是我的第一个猜测:

  time_t current;
  time(&current);
  struct tm dateDetails;
  ACE_OS::localtime_r(&current, &dateDetails);

  // Get the current session start time
  const time_t yearToTime     = dateDetails.tm_year - 70; // year to 1900 converted into year to 1970
  const time_t ydayToTime     = dateDetails.tm_yday;
  const time_t midnightTime   = (yearToTime * 365 * 24 * 60 * 60) + (ydayToTime* 24 * 60 * 60);
  StartTime_                  = static_cast<long>(current - midnightTime);

Answer 1

您可以使用标准C API:

1. 获取当前时间time().
2. 将其转换为struct tm与gmtime_r()或localtime_r().
3. 它的设置tm_sec,tm_min,tm_hour到零.
4. 其转换回time_t用mktime().
5. 找出原始time_t值和新值之间的差异.

例:

#include <time.h>
#include <stdio.h>

time_t
day_seconds() {
    time_t t1, t2;
    struct tm tms;
    time(&t1);
    localtime_r(&t1, &tms);
    tms.tm_hour = 0;
    tms.tm_min = 0;
    tms.tm_sec = 0;
    t2 = mktime(&tms);
    return t1 - t2;
}

int
main() {
    printf("seconds since the beginning of the day: %lu\n", day_seconds());
    return 0;
}

Answer 2

还可以对一天中的秒数取模：

 return nbOfSecondsSince1970 % (24 * 60 * 60)