Visual C++ Debugging: How do I evaluate the time difference between two events?

[Pravin Kumar]

Q: How do I evaluate the time difference between two events?

A: Accurate time difference between events cannot be evaluated by clocking the time using 'CTime::GetCurrentTime()' or by using a timer. First method is limited in its accuracy to around a second and second method has limitations of lower priority.

Here I present a function which returns the time elapsed from the last call. First call will always return a zero value. This uses the high-resolution performance counter. If it does not exist, each call will return zero.

float TimeDiff()
{
  // Last counter reading
  static LARGE_INTEGER OldCounter = {0, 0};

  LARGE_INTEGER Counter, Frequency;
  if (QueryPerformanceFrequency(&Frequency))
  {
    // Gets current counter reading
    QueryPerformanceCounter(&Counter);

    // Calculates time difference (zero if called first time)
    float TimeDiff = OldCounter.LowPart ? (float) (Counter.LowPart - OldCounterLowPart) / Frequency.LowPart : 0;

    // Resets last counter reading
    OldCounter = Counter;

    // Returns time difference
    return TimeDiff;
  }
  else
  {
    // No high resolution performance counter; returns zero
    return 0;
  }
}

Time difference is returned in seconds and the accuracy is determined by the high-resolution performance counter frequency.