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timeGetTime vs. QueryPerformanceCounter

timeGetTime vs. QueryPerformanceCounter

timeGetTime vs. QueryPerformanceCounter

Something I was curious about as I was trying to get some good program timing code working:

I notice these two values aren't anywhere in sync in terms of what the numbers are.  (This is after I take QPC / (QPF / 1000) of course.)  I was wondering if anyone knew the difference between the two numbers and where they came from.

Is QPC/QPF somehow hardware dependent compared to timeGetTime being software?  Or is there some other explanation?

RE: timeGetTime vs. QueryPerformanceCounter

What's a problem?
1. Yes, QPF returned value is hardware dependent (but it's not a CPU frequency!).
2. timeGetTime has 1 millisecond precision by default (too low;).
3. To obtain short time interval(s) by QPF/QPC calls:


#include <windows.h>
  f,  /* HPC ticks per second */
  t0, /* start counter */
  t1; /* end counter value */
double micros; // want in microseconds, see 1e6 constant
if (QueryPerformanceFrequency(&f))
   printf("Performance Frequency is %d\n",(int)f.QuadPart);
   if (QueryPerformanceCounter(&t0))
      /* ** tested code here ** */
      if (QueryPerformanceCounter(&t1))
         micros = (double)(t1.QuadPart - t0.QuadPart) * 1e6
         printf("Elapse time is %g microseconds\n",micros);
   printf("*** QPF failed.\n");

RE: timeGetTime vs. QueryPerformanceCounter

Sorry, must be (double)f.QuadPart divider...

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