type errors in simple maths

[martin]

I have this

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LARGE_INTEGER lFreq, lNow, lLast, lElapsed;

QueryPerformanceFrequency(&lFreq);
QueryPerformanceCounter(&lNow);
 
    lElapsed = (lNow - lLast) * 1000/lFreq;//mS <-errors


I get errors as follows

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error #2168: Operands of - have incompatible types 'LARGE_INTEGER' and 'LARGE_INTEGER'.
error #2168: Operands of / have incompatible types 'int' and 'LARGE_INTEGER'.
error #2168: Operands of = have incompatible types 'LARGE_INTEGER' and 'int'.
error #2168: Operands of > have incompatible types 'LARGE_INTEGER' and 'int'.


I have tried casting the LARGE_INTEGERS to float but this is not allowed, and I have tried many other things but I obviously don't understand some basics.
Can someone point me to somewhere that explains how I do something so simple as a this little calculation.

Even these give errors.

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lElapsed = lNow - lLast;
lElapsed -= lNow;


The same types of calculation can be made in Visual C++ without errors.

[Romashka]

seems like LARGE_INTEGER is not defined correctly 
can you post a definition of this type?
and are you sure the file that defines it is #included?

[martin]

Thanks Romashka, that gave me the answer. I thought that LARGE_INTEGER was long long or int64, but after seeing your post I looked up the definition and it is a union. So to use the values I want I have to say

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QueryPerformanceFrequency(&lFreq);
QueryPerformanceCounter(&lNow);

lElapsed.QuadPart = (lNow.QuadPart - lLast.QuadPart) * 1000/lFreq.QuadPart;//mS

and it works!
Thanks. (Great progress for me  )

[Robert]

Hi Martin:

It may "work" but does it do so correctly?

Robert Wishlaw

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#include <windows.h>
#include <stdio.h>
#include <time.h> // contains needed prototype for _sleep function

// User Global Variables
static LARGE_INTEGER lFreq, lLast, lNow, lElapsed;
static double RElapsed;
static int RetVal;

void main(void) {

RetVal = QueryPerformanceFrequency(&lFreq);
if(RetVal == 0)
  {
    printf("%s\n","This computer does not have a high-performance timer.");
    fflush(stdout);
    ExitProcess(0);
  }

printf("%s\n", "Pelle's C _sleep ");
QueryPerformanceCounter(&lLast);
_sleep(2);
QueryPerformanceCounter(&lNow);

  lElapsed.QuadPart = (lNow.QuadPart - lLast.QuadPart) * 1000/lFreq.QuadPart;//mS
  printf("%s% .15G%s\n", "did not last ", (double)lElapsed.QuadPart, " seconds,");

  RElapsed = (double)(((lNow.QuadPart - lLast.QuadPart) * (1.0 / lFreq.QuadPart)));
  printf("%s% .15G%s\n", "it lasted ", RElapsed, " seconds.");
}



[Robert]

Also, NOTE WELL that on some computers hardware errata exists that confounds the QueryPerformanceCounter function. Specifically, the result that is returned by the QueryPerformanceCounter function may unexpectedly leap forward from time to time. This leap may represent several seconds.  For more details see

'Performance counter value may unexpectedly leap forward'

available at

http://support.microsoft.com/kb/274323

Robert Wishlaw