How to use QueryPerformanceCounter

Question

I recently decided that I needed to change from using milliseconds to microseconds for my Timer class  and after some research I ve decided that QueryPerformanceCounter is probably my safest bet   The warning on Boost  Posix that it may not works on Win32 API put me off a bit   However  I m not really sure how to implement it    What I m doing is calling whatever GetTicks   esque function I m using and assigning it to Timer s startingTicks variable  Then to find the amount of time passed I just subtract the function s return value from the startingTicks  and when I reset the timer I just call the function again and assign startingTicks to it  Unfortunately  from the code I ve seen it isn t as simple as just calling QueryPerformanceCounter    and I m not sure what I m supposed to pass as its argument

User · Answer

I use these defines       Use to init the clock     define TIMER INIT       LARGE INTEGER frequency        LARGE INTEGER t1 t2        double elapsedTime        QueryPerformanceFrequency  amp frequency         Use to start the performance timer     define TIMER START QueryPerformanceCounter  amp t1        Use to stop the performance timer and output the result to the standard stream  Less verbose than  c TIMER STOP VERBOSE     define TIMER STOP       QueryPerformanceCounter  amp t2         elapsedTime  float  t2 QuadPart-t1 QuadPart  frequency QuadPart        std  wcout lt  lt elapsedTime lt  lt L  sec  lt  lt endl    Usage  brackets to prevent redefines    TIMER INIT       TIMER START    Sleep 1000      TIMER STOP         TIMER START    Sleep 1234      TIMER STOP     Output from usage example   1 00003 sec 1 23407 sec

User · Answer

include  lt windows h gt   double PCFreq   0 0    int64 CounterStart   0   void StartCounter         LARGE INTEGER li      if  QueryPerformanceFrequency  amp li       cout  lt  lt   QueryPerformanceFrequency failed  n        PCFreq   double li QuadPart  1000 0       QueryPerformanceCounter  amp li       CounterStart   li QuadPart    double GetCounter         LARGE INTEGER li      QueryPerformanceCounter  amp li       return double li QuadPart-CounterStart  PCFreq     int main         StartCounter        Sleep 1000       cout  lt  lt  GetCounter    lt  lt   n       return 0      This program should output a number close to 1000  windows sleep isn t that accurate  but it should be like 999    The StartCounter   function records the number of ticks the performance counter has in the CounterStart variable  The GetCounter   function returns the number of milliseconds since StartCounter   was last called as a double  so if GetCounter   returns 0 001 then it has been about 1 microsecond since StartCounter   was called   If you want to have the timer use seconds instead then change  PCFreq   double li QuadPart  1000 0    to  PCFreq   double li QuadPart     or if you want microseconds then use  PCFreq   double li QuadPart  1000000 0    But really it s about convenience since it returns a double

User · Answer

I would extend this question with a NDIS driver example on getting time  As one knows  KeQuerySystemTime  mimicked under NdisGetCurrentSystemTime  has a low resolution above milliseconds  and there are some processes like network packets or other IRPs which may need a better timestamp   The example is just as simple   LONG INTEGER data  frequency  LONGLONG diff  data   KeQueryPerformanceCounter  LARGE INTEGER    amp frequency  diff   data QuadPart    Frequency QuadPart  divisor    where divisor is 10 3  or 10 6 depending on required resolution

User · Answer

Assuming you re on Windows  if so you should tag your question as such    on this MSDN page you can find the source for a simple  useful HRTimer C   class that wraps the needed system calls to do something very close to what you require  it would be easy to add a GetTicks   method to it  in particular  to do exactly what you require    On non-Windows platforms  there s no QueryPerformanceCounter function  so the solution won t be directly portable   However  if you do wrap it in a class such as the above-mentioned HRTimer  it will be easier to change the class s implementation to use what the current platform is indeed able to offer  maybe via Boost or whatever

[c++] How to use QueryPerformanceCounter?

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