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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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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.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for XCOM Labs
void Void(void) { Void(); } /* The recursive call of the void */

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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++ ? 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++ ? Michael S <already5chosen@yahoo.com> - 2022-11-06 14:30 -0800
        Re: what is the best way to get microseconds of time on Windows in C or C++ ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-11-07 07:48 +0100
          Re: what is the best way to get microseconds of time on Windows in C or C++ ? Michael S <already5chosen@yahoo.com> - 2022-11-07 04:11 -0800
            Re: what is the best way to get microseconds of time on Windows in C or C++ ? "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-11-08 18:30 +0100
              Re: what is the best way to get microseconds of time on Windows in C or C++ ? Michael S <already5chosen@yahoo.com> - 2022-11-08 15:37 -0800
                Re: what is the best way to get microseconds of time on Windows in C or C++ ? Öö Tiib <ootiib@hot.ee> - 2022-11-09 06:14 -0800
                Re: what is the best way to get microseconds of time on Windows in C or C++ ? Michael S <already5chosen@yahoo.com> - 2022-11-12 16:21 -0800
  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++ ? Michael S <already5chosen@yahoo.com> - 2022-11-06 14:41 -0800
            Re: what is the best way to get microseconds of time on Windows in C or C++ ? scott@slp53.sl.home (Scott Lurndal) - 2022-11-07 14:39 +0000
              Re: what is the best way to get microseconds of time on Windows in C or C++ ? Michael S <already5chosen@yahoo.com> - 2022-11-07 11:03 -0800
            Re: what is the best way to get microseconds of time on Windows in C or C++ ? Lynn McGuire <lynnmcguire5@gmail.com> - 2022-11-07 23:26 -0600
  Re: what is the best way to get microseconds of time on Windows in C or C++ ? Öö Tiib <ootiib@hot.ee> - 2022-11-04 01:23 -0700
    Re: what is the best way to get microseconds of time on Windows in C or C++ ? Juha Nieminen <nospam@thanks.invalid> - 2022-11-07 07:20 +0000
      Re: what is the best way to get microseconds of time on Windows in C or C++ ? Öö Tiib <ootiib@hot.ee> - 2022-11-07 07:11 -0800
  Re: what is the best way to get microseconds of time on Windows in C or C++ ? Michael S <already5chosen@yahoo.com> - 2022-11-04 03:12 -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 14:35 -0500
  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++ ? Manu Raju <MR@invalid.invalid> - 2022-11-20 21:30 +0000

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