How Can I Accurately Measure Elapsed Time Using QueryPerformanceCounter in Windows?

How to Determine Elapsed Time with QueryPerformanceCounter

QueryPerformanceCounter is a high-resolution performance counter API for Windows systems that allows for precise timing measurements. To implement it, follow these steps:

1. Include Necessary Headers:

   #include <windows.h>

2. Define Performance Counter Variables:

   • PCFreq: Double variable to store the counter frequency in milliseconds.
   • CounterStart: Integer variable to store the starting counter value.

3. Implement StartCounter Function:

   • Get the performance counter frequency in hertz using QueryPerformanceFrequency.
   • Convert the frequency to milliseconds.
   • Get the starting counter value using QueryPerformanceCounter.

4. Implement GetCounter Function:

   • Get the current counter value using QueryPerformanceCounter.
   • Subtract the starting counter value to get the elapsed time in milliseconds.
   • Convert the elapsed time to the desired unit (e.g., seconds, microseconds).

5. Example Usage:

   • Call StartCounter() to initialize the performance counter.
   • Use Sleep or a similar function to wait for a specific duration.
   • Call GetCounter() to retrieve the elapsed time.

Code Snippet:

double PCFreq = 0.0;
__int64 CounterStart = 0;

void StartCounter()
{
    LARGE_INTEGER li;
    if (!QueryPerformanceFrequency(&li))
        cout << "QueryPerformanceFrequency failed!\n";

    PCFreq = double(li.QuadPart) / 1000.0;

    QueryPerformanceCounter(&li);
    CounterStart = li.QuadPart;
}

double GetCounter()
{
    LARGE_INTEGER li;
    QueryPerformanceCounter(&li);
    return double(li.QuadPart - CounterStart) / PCFreq;
}

int main()
{
    StartCounter();
    Sleep(1000);
    cout << GetCounter() << "\n";
    return 0;
}

This code snippet outputs a value close to 1000, demonstrating the use of QueryPerformanceCounter for precise timing measurements.

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