Windows API Timer with microsecond (or better) accuracy.

by Curtis Krauskopf

Q:  I need a timer timer with a 1 microsecond (1,000,000^th of a second) accuracy.

A:  You need to use the high resolution performance counter that is available in the QueryPerformanceCounter() function.  It is able to provide times that exceed 1 microsecond accuracy on most hardware.

The availability of the QueryPerformanceCounter() is dependent.on the system's hardware.  To find out if it's available, and to find out its accuracy, use the QueryPerformanceFrequency() function. 

The QueryPerformanceCounter() function returns the amount of time that has elapsed since the system was booted.  Elapsed time can be found by comparing the returned values at two different points in time.

Here's an example of getting the amount of time since the system has started:

#include <windows.h> #include <stdio.h> ... ...   LARGE_INTEGER ticksPerSecond;   LARGE_INTEGER tick;   // A point in time   LARGE_INTEGER time;   // For converting tick into real time   // get the high resolution counter's accuracy   QueryPerformanceFrequency(&ticksPerSecond);   // what time is it?   QueryPerformanceCounter(&tick);   // convert the tick number into the number of seconds   // since the system was started...   time.QuadPart = tick.QuadPart/ticksPerSecond.QuadPart;   //get the number of hours   int hours = time.QuadPart/3600;   //get the number of minutes   time.QuadPart = time.QuadPart - (hours * 3600);   int minutes = time.QuadPart/60;   //get the number of seconds   int seconds = time.QuadPart - (minutes * 60);   AnsiString result = "The system was started ";   result += IntToStr(hours) + " hours ";   result += IntToStr(minutes) + " minutes ";   result += IntToStr(seconds) + " and ";   result += AnsiString(tick.QuadPart % ticksPerSecond.QuadPart);   result += AnsiString("/") + ticksPerSecond.QuadPart;   result += " seconds ago.";   printf("%s", result.c_str());

	Output: The system was started 1 hours 29 minutes 30 and 9713/1193180 seconds ago.

Ignore the Conversion may lose significant digits warnings when compiling this sample.  The compiler doesn't know that most computers are not on for 2 billion hours (0x7FFFFFFF) without being rebooted!

This article was written by Curtis Krauskopf (email at ).

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