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Re: what is the best way to get microseconds of time on Windows in C or C++ ?

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On 11/4/2022 11:07 AM, Keith Thompson wrote:
> Lynn McGuire <lynnmcguire5@gmail.com> writes:
>> On 11/3/2022 8:51 PM, DFS wrote:
>>> On 11/3/2022 9:14 PM, Lynn McGuire wrote:
>>>> What is the best way to get microseconds of time on Windows in C or
>>>> C++ ?  I am currently using the following code to get the current
>>>> time:
>>>>
>>>>       std::time_t t = std::time (0);   // get time now
>>>>       std::tm * now = std::localtime ( & t);
>>>>       integer iyear = now -> tm_year + 1900;
>>>>       integer imonth = now -> tm_mon + 1;
>>>>       integer iday = now -> tm_mday;
>>>>       integer ihour = now -> tm_hour;
>>>>       integer imin = now -> tm_min;
>>>>       integer isec = now -> tm_sec;
>>>>       integer ihund = 0;
>>>>
>>>> Thanks,
>>>> Lynn
>>>
>>> https://learn.microsoft.com/en-us/windows/win32/sysinfo/acquiring-high-resolution-time-stamps
>>>
>>> I used it like this:
>>> ----------------------------------------------------------------
>>> LARGE_INTEGER frequency,start,end;
>>> //calc elapsed time
>>> double elapsedtime(LARGE_INTEGER startingtimer)
>>> {
>>>     QueryPerformanceCounter(&end);
>>>     return (end.QuadPart - startingtimer.QuadPart) /
>>> (double)frequency.QuadPart;
>>> }
>>>
>>> int main(void)
>>> {
>>>       //turn on Windows program timing
>>>       QueryPerformanceFrequency(&frequency);
>>>       //start timing a piece of code
>>>       QueryPerformanceCounter(&start);
>>>       ...
>>>       ...
>>>       printf(" %.4fs to execute\n",elapsedtime(start));
>>> }
>>> ----------------------------------------------------------------
>>
>> I forgot to add I would prefer a portable way if possible.  I suspect
>> that is not possible though below the second resolution.
> 
> The resolution of the time() function is unspecified (not even
> implementation-defined).  In practice, time_t is almost universally an
> integer type representing seconds since some epoch, usually 1970-01-01
> 00:00:00 UTC, but it could even be floating-point.
> 
> C11 adds the type struct timespec and the function timespec_get() which
> gives a result with a resolution of 1 nanosecond.  A footnote in the
> standard says:
> 
>      Although a struct timespec object describes times with nanosecond
>      resolution, the available resolution is system dependent and may
>      even be greater than 1 second.
> 
> The standard says that struct timespec has the following members:
> 
>      time_t tv_sec; // whole seconds — ≥ 0
>      long tv_nsec; // nanoseconds — [0, 999999999]
> 
> which strongly implies that the resulution of time_t is 1 second, but
> the standard still doesn't say so.  Possibly an implementation could use
> different encodings for the time_t value from time() and the time_t
> value from timespec_get(), though that's unlikely in practice.
> 
> clock() returns a value of type clock_t, which is typically double, but
> that's also unspecified -- and it measures processor time, not wall
> clock time.

Thanks !

Lynn

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Thread

what is the best way to get microseconds of time on Windows in C or C++ ? Lynn McGuire <lynnmcguire5@gmail.com> - 2022-11-03 20:14 -0500
  Re: what is the best way to get microseconds of time on Windows in C or C++ ? DFS <nospam@dfs.com> - 2022-11-03 21:51 -0400
    Re: what is the best way to get microseconds of time on Windows in C or C++ ? Lynn McGuire <lynnmcguire5@gmail.com> - 2022-11-04 00:06 -0500
      Re: what is the best way to get microseconds of time on Windows in C or C++ ? Christian Gollwitzer <auriocus@gmx.de> - 2022-11-04 08:03 +0100
        Re: what is the best way to get microseconds of time on Windows in C or C++ ? Lynn McGuire <lynnmcguire5@gmail.com> - 2022-11-04 14:32 -0500
      Re: what is the best way to get microseconds of time on Windows in C or C++ ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-11-04 09:07 -0700
        Re: what is the best way to get microseconds of time on Windows in C or C++ ? Lynn McGuire <lynnmcguire5@gmail.com> - 2022-11-04 14:33 -0500
      Re: what is the best way to get microseconds of time on Windows in C or C++ ? Opus <ifonly@youknew.org> - 2022-11-06 20:53 +0100
  Re: what is the best way to get microseconds of time on Windows in C or C++ ? Juha Nieminen <nospam@thanks.invalid> - 2022-11-04 07:35 +0000
    Re: what is the best way to get microseconds of time on Windows in C or C++ ? Lynn McGuire <lynnmcguire5@gmail.com> - 2022-11-04 14:24 -0500
      Re: what is the best way to get microseconds of time on Windows in C or C++ ? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2022-11-04 19:50 +0000
        Re: what is the best way to get microseconds of time on Windows in C or C++ ? Lynn McGuire <lynnmcguire5@gmail.com> - 2022-11-04 15:16 -0500
      Re: what is the best way to get microseconds of time on Windows in C or C++ ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-11-04 15:05 -0700
        Re: what is the best way to get microseconds of time on Windows in C or C++ ? Lynn McGuire <lynnmcguire5@gmail.com> - 2022-11-04 17:35 -0500
          Re: what is the best way to get microseconds of time on Windows in C or C++ ? "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-11-04 15:56 -0700
          Re: what is the best way to get microseconds of time on Windows in C or C++ ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-11-04 16:15 -0700
  Re: what is the best way to get microseconds of time on Windows in C or C++ ? scott@slp53.sl.home (Scott Lurndal) - 2022-11-04 13:44 +0000
    Re: what is the best way to get microseconds of time on Windows in C or C++ ? Lynn McGuire <lynnmcguire5@gmail.com> - 2022-11-04 14:34 -0500
    Re: what is the best way to get microseconds of time on Windows in C or C++ ? Lynn McGuire <lynnmcguire5@gmail.com> - 2022-11-14 16:58 -0600
      Re: what is the best way to get microseconds of time on Windows in C or C++ ? Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-11-14 17:36 -0800
        Re: what is the best way to get microseconds of time on Windows in C or C++ ? Lynn McGuire <lynnmcguire5@gmail.com> - 2022-11-15 17:26 -0600
          Re: what is the best way to get microseconds of time on Windows in C or C++ ? Andreas <nospam@gmx.de> - 2022-11-16 13:15 +0100
  Re: what is the best way to get microseconds of time on Windows in C or C++ ? Bonita Montero <Bonita.Montero@gmail.com> - 2022-11-04 20:49 +0100
    Re: what is the best way to get microseconds of time on Windows in C or C++ ? Bart <bc@freeuk.com> - 2022-11-04 22:31 +0000
      Re: what is the best way to get microseconds of time on Windows in C or C++ ? Bonita Montero <Bonita.Montero@gmail.com> - 2022-11-05 06:40 +0100
  Re: what is the best way to get microseconds of time on Windows in C or C++ ? Manu Raju <MR@invalid.invalid> - 2022-11-20 21:30 +0000

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