Thread: QueryPerformanceCounter & Frequency

Hi, can anybody tell me what do they mean with QueryPerformanceCounter and QueryPerformanceFrequency? And also, what are they implemented for? Thanks in advance.

Quotes from MSDN:

Originally Posted by MSDN

The QueryPerformanceCounter function retrieves the current value of the high-resolution performance counter.

Originally Posted by MSDN

The QueryPerformanceFrequency function retrieves the frequency of the high-resolution performance counter, if one exists. The frequency cannot change while the system is running.

lpFrequency
[out] Pointer to a variable that receives the current performance-counter frequency, in counts per second. If the installed hardware does not support a high-resolution performance counter, this parameter can be zero.

I've read the MSDN but I still can't figure out the use of them in real application. I mean, it's basically similar to the "time.h" functions. So, what are they actually used for? As of now, the only time I use them is in some kind of timeout mechanism. I chose them because I figured it's from Microsoft and I'm programming for Windows so maybe it's better to use it than "time.h". Or maybe I'm wrong. CMIIW.

EDIT: BTW, I also didn't quite understand the part of MSDN that said: "high-resolution performance counter." It's so vague IMHO.

It does the same thing as the time.h functions, only they're Windows API and will not work on any other platform.
They may also have higher precision than time.h, but I cannot say for sure.

Why do you ask? I'm sure there are HUNDREDS of Windows API calls that I've never heard of or used.

But to answer your question: It gives better precision than clock() or time(). The frequency would be at the very least above 1MHz, it may be as high as GHz. It is also different from clock() in that it counts wallclock time, not CPU time - this may be good or bad, depending on what you want to do.

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Mats

Originally Posted by matsp

Why do you ask? I'm sure there are HUNDREDS of Windows API calls that I've never heard of or used.
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Mats

Well, I'm working on Torque Game Engine right now and I see some calls of the functions in the source code. So I figured maybe I need them if I intend to make my own engine in the future. And I was just curious, that's all. I'm still new in the Windows programming myself.

Thanks a lot guys.

Windows's buggy clock() actually measures wall time, if I remember correctly.

Originally Posted by CornedBee

Windows's buggy clock() actually measures wall time, if I remember correctly.

Still? I know DOS used to be that way, but I thought they'd fixed it - oh well, it's been a long time since last time I used clock() to measure anything where background tasks was a measurable percentage of the time anyways.

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Mats