Subj : Re: high resolution time function under visual c++ environment?
To   : comp.programming
From : websnarf
Date : Wed Aug 03 2005 04:37 pm

wavelet wrote:
> I am searching one time function under windows2000
> with Visual C++ environment. Is there function available
> like gethrtime() in unix? Thx.
>
> #include <sys/time.h>
>
> main()
> {
>      hrtime_t start, end;
>      int i, iters = 100;
>
>      start = gethrtime();
>      for (i = 0; i < iters; i++)
>              getpid();
>      end = gethrtime();
>      printf("Avg getpid() time = %lld nsec\n", (end - start) / iters);
> }

If you include the WinMM library, you can use the
QueryPerformanceCounter() function to get access to the on-chip cycle
counter, which is really as precise and you can get.

The problem with using it is that it doesn't take "power savings modes"
(which may include down-clocking the CPU) of the processor into
account.  So you might like to do something like compare it to the
incremental results of time(NULL) (or in fact clock(), since most
Windows compilers don't subtract time not given to the process for that
call) and if there is a sufficiently high deviation, you can
recalibrate it via the QueryPerformanceFrequency() call.  You might
need to do tricks to make sure that the output remains monotonic.  Of
course you have to keep in mind that for most Windows compilers,
time(NULL) will stop functioning properly in 2038.

Hmm ... thinking about all this, I would be highly surprised if there
wasn't a better solution somewhere.  :)

-- 
Paul Hsieh
http://www.pobox.com/~qed/
http://bstring.sf.net/

.