See, for example, How to realise long-term high-resolution timing on windows using C++? and C++ Timer function to provide time in nano seconds.
I have done some testing with Cygwin under Windows XP: on my machine, the granularity of gettimeofday() is about 15 msecs (~1/64 secs). Which is quite coarse. And so is the granularity of:
* clock_t clock(void) (divisor CLOCKS_PER_SEC)
* clock_t times(struct tms *) (divisor sysconf(_SC_CLK_TCK))
Both divisors are 1000 (POSIX may have 1000000 for first).
Also, clock_getres(CLOCK_REALTIME,...) returns 15 msecs, so clock_gettime() is unlikely to help. And CLOCK_MONOTONIC and CLOCK_PROCESS_CPUTIME_ID don't work.
Other possibilites for Windows might be RDTSC; see the Wikipedia article. And HPET, which isn't available with Windows XP.
Also note in Linux, clock() is the process time, while in Windows it is the wall time.
So some sample code, both for standard Unix, and for CYGWIN code running under Windows, which gives a granularity of about 50 microsecs (on my machine). The return value is in seconds, and gives the number of seconds elapsed since the function was first called. (I belatedly realized this was in an answer I gave over a year ago).
#ifndef __CYGWIN32__
double RealElapsedTime(void) { // returns 0 seconds first time called
static struct timeval t0;
struct timeval tv;
gettimeofday(&tv, 0);
if (!t0.tv_sec)
t0 = tv;
return tv.tv_sec - t0.tv_sec + (tv.tv_usec - t0.tv_usec) / 1000000.;
}
#else
#include <windows.h>
double RealElapsedTime(void) { // granularity about 50 microsecs on my machine
static LARGE_INTEGER freq, start;
LARGE_INTEGER count;
if (!QueryPerformanceCounter(&count))
FatalError("QueryPerformanceCounter");
if (!freq.QuadPart) { // one time initialization
if (!QueryPerformanceFrequency(&freq))
FatalError("QueryPerformanceFrequency");
start = count;
}
return (double)(count.QuadPart - start.QuadPart) / freq.QuadPart;
}
#endif
