using gettimeofday() equivalents on windows - c

Question

I'm trying to use 2 different equivalents for UNIX's gettimeofday() function on Windows, using Visual Studio 2013.
I took the first one from here. As the second one, I'm using the _ftime64_s function, as explained here.
They work, but not as I expected. I want to get different values when printing the seconds, or at least the milliseconds, but I get the same value for the printings with gettimeofday() (mytime1 & mytime2) and with _ftime64_s (mytime3 & mytime4).
However, it worth mentioning that the value of the milliseconds is indeed different between these two functions (that is, the milliseconds value of mytime1/mytime2 is different from mytime3/mytime4).
Here's my code:
#include <stdio.h>
#include <Windows.h>
#include <stdint.h>
#include <sys/timeb.h>
#include <time.h>
#define WIN32_LEAN_AND_MEAN
int gettimeofday(struct timeval * tp, struct timezone * tzp)
{
// Note: some broken versions only have 8 trailing zero's, the correct epoch has 9 trailing zero's
static const uint64_t EPOCH = ((uint64_t)116444736000000000ULL);
SYSTEMTIME system_time;
FILETIME file_time;
uint64_t time;
GetSystemTime(&system_time);
SystemTimeToFileTime(&system_time, &file_time);
time = ((uint64_t)file_time.dwLowDateTime);
time += ((uint64_t)file_time.dwHighDateTime) << 32;
tp->tv_sec = (long)((time - EPOCH) / 10000000L);
tp->tv_usec = (long)(system_time.wMilliseconds * 1000);
return 0;
}
int main()
{
/* working with struct timeval and gettimeofday equivalent */
struct timeval mytime1;
struct timeval mytime2;
gettimeofday(&(mytime1), NULL);
gettimeofday(&(mytime2), NULL);
printf("Seconds: %d\n", (int)(mytime1.tv_sec));
printf("Milliseconds: %d\n", (int)(mytime1.tv_usec));
printf("Seconds: %d\n", (int)(mytime2.tv_sec));
printf("Milliseconds: %d\n", (int)(mytime2.tv_usec));
/* working with _ftime64_s */
struct _timeb mytime3;
struct _timeb mytime4;
_ftime64_s(&mytime3);
_ftime64_s(&mytime4);
printf("Seconds: %d\n", mytime3.time);
printf("Milliseconds: %d\n", mytime3.millitm);
printf("Seconds: %d\n", mytime4.time);
printf("Milliseconds: %d\n", mytime4.millitm);
return (0);
}
I tried other format specifiers (%f, %lu) and castings ((float), (double), (long), (size_t)), but it didn't matter. Suggestions will be welcomed.

Answer 1

QueryPerformanceCounter is used for accurate timing on windows. Usage can be as follows:
uint64_t microseconds()
{
LARGE_INTEGER fq, t;
QueryPerformanceFrequency(&fq);
QueryPerformanceCounter(&t);
return (1000000 * t.QuadPart) / fq.QuadPart;
}
This does not work with any EPOCH as far as I know. For that you need GetSystemTimePreciseAsFileTime which is only available on Windows 8 and higher.
uint64_t MyGetSystemTimePreciseAsFileTime()
{
HMODULE lib = LoadLibraryW(L"kernel32.dll");
if (!lib) return 0;
FARPROC fp = GetProcAddress(lib, "GetSystemTimePreciseAsFileTime");
ULARGE_INTEGER largeInt;
largeInt.QuadPart = 0;
if (fp)
{
T_GetSystemTimePreciseAsFileTime* pfn = (T_GetSystemTimePreciseAsFileTime*)fp;
FILETIME fileTime = { 0 };
pfn(&fileTime);
largeInt.HighPart = fileTime.dwHighDateTime;
largeInt.LowPart = fileTime.dwLowDateTime;
}
FreeLibrary(lib);
return largeInt.QuadPart;
}
int main()
{
uint64_t t1 = microseconds();
uint64_t t2 = microseconds();
printf("t1: %llu\n", t1);
printf("t2: %llu\n", t2);
return (0);
}