为什么微秒时间戳使用(私有)gettimeoftheday()重复，即纪元

================================= //Full Program

#include <iostream>
#include <windows.h>
#include <conio.h>
#include <time.h>
#include <stdio.h>

#if defined(_MSC_VER) || defined(_MSC_EXTENSIONS)
  #define DELTA_EPOCH_IN_MICROSECS  11644473600000000Ui64
#else
  #define DELTA_EPOCH_IN_MICROSECS  11644473600000000ULL
#endif

struct timezone 
{
  int  tz_minuteswest; /* minutes W of Greenwich */
  int  tz_dsttime;     /* type of dst correction */
};

timeval capture_time;  // structure

int gettimeofday(struct timeval *tv, struct timezone *tz)
{
  FILETIME ft;
  unsigned __int64 tmpres = 0;
  static int tzflag;

  if (NULL != tv)
  {
    GetSystemTimeAsFileTime(&ft);

    tmpres |= ft.dwHighDateTime;
    tmpres <<= 32;
    tmpres |= ft.dwLowDateTime;

    /*converting file time to unix epoch*/
    tmpres -= DELTA_EPOCH_IN_MICROSECS; 
    tmpres /= 10;  /*convert into microseconds*/
    tv->tv_sec = (long)(tmpres / 1000000UL);
    tv->tv_usec = (long)(tmpres % 1000000UL);
  }

  if (NULL != tz)
  {
    if (!tzflag)
    {
      _tzset();
      tzflag++;
    }

    tz->tz_minuteswest = _timezone / 60;
    tz->tz_dsttime = _daylight;
  }

  return 0;
}

int main()
{
   while(1)
  {     
    gettimeofday(&capture_time, NULL);     
    printf(".%ld
", capture_time.tv_usec);// JUST PRINTING MICROSECONDS    
   }    
}

推荐答案

你观察到的时间变化是 0.414719 s 到 0.430344 s.差异为 15.615 毫秒.数字的表示是微秒这一事实不意味着它增加了 1 微秒.事实上，我预计 15.625 毫秒.这是标准硬件上的系统时间增量.我仔细看看 这里 和 这里.这称为系统时间的粒度.

#define TARGET_PERIOD 1         // 1-millisecond target interrupt period


TIMECAPS tc;
UINT     wTimerRes;

if (timeGetDevCaps(&tc, sizeof(TIMECAPS)) != TIMERR_NOERROR) 
// this call queries the systems timer hardware capabilities
// it returns the wPeriodMin and wPeriodMax with the TIMECAPS structure
{
  // Error; application can't continue.
}

// finding the minimum possible interrupt period:

wTimerRes = min(max(tc.wPeriodMin, TARGET_PERIOD ), tc.wPeriodMax);
// and setting the minimum period:

timeBeginPeriod(wTimerRes);