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Groups > comp.lang.c++ > #83537

Re: Adjusting printf() rounding

From Paavo Helde <eesnimi@osa.pri.ee>
Newsgroups comp.lang.c++
Subject Re: Adjusting printf() rounding
Date 2022-04-08 19:38 +0300
Organization A noiseless patient Spider
Message-ID <t2podd$ubk$1@dont-email.me> (permalink)
References <t2pag0$eab$1@dont-email.me> <t2pnek$3f5em$1@gwaiyur.mb-net.net>

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08.04.2022 19:21 Marcel Mueller kirjutas:

>> For me this means we have nasty cross-platform differences which we 
>> would rather try to avoid. How could we coerce glibc() to round up, or 
>> failing that, coerce MSVC to round down?
> 
> Why should you care about that difference?
> 
> If you have more complex calculations with floating point numbers not 
> only the last digit is indeterminate. E.g. transcendental functions 
> typically do not provide the maximum possible precision in many FPU 
> implementations.
> 
> And if you depend on a specific rounding mode you should use your own 
> rounding with round/floor/ceil which have well defined behavior.

I'm not concerned about the last (16-th) digit at all. In this case, I'm 
concerned about the third digit.

printf("%.3g\n", 212.5) yields 212 in Linux and 213 on Windows.

Even if we could swallow it ourselves, it would be hard to explain our 
customers why our software works inconsistently cross platform.

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Thread

Adjusting printf() rounding Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-08 15:40 +0300
  Re: Adjusting printf() rounding Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-08 06:02 -0700
  Re: Adjusting printf() rounding Marcel Mueller <news.5.maazl@spamgourmet.org> - 2022-04-08 18:21 +0200
    Re: Adjusting printf() rounding Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-08 19:38 +0300
      Re: Adjusting printf() rounding Sams Lara <samlara622@gmail.com> - 2022-04-08 18:48 +0100
        Re: Adjusting printf() rounding Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-08 23:44 +0300
          Re: Adjusting printf() rounding Marcel Mueller <news.5.maazl@spamgourmet.org> - 2022-04-09 12:58 +0200
            Re: Adjusting printf() rounding Geoff <geoff@invalid.invalid> - 2022-04-09 08:45 -0700
            Re: Adjusting printf() rounding Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-04-09 13:05 -0700
              Re: Adjusting printf() rounding red floyd <no.spam.here@its.invalid> - 2022-04-09 13:36 -0700
            Re: Adjusting printf() rounding Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-09 16:08 -0700
  Re: Adjusting printf() rounding Manfred <noname@add.invalid> - 2022-04-08 21:30 +0200
  Re: Adjusting printf() rounding "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-04-09 10:11 +0200
    Re: Adjusting printf() rounding Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-10 16:39 +0300
      Re: Adjusting printf() rounding Sams Lara <samlara622@gmail.com> - 2022-04-10 18:36 +0100
        Re: Adjusting printf() rounding Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-10 21:50 +0300
  Re: Adjusting printf() rounding Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-09 09:05 -0700
    Re: Adjusting printf() rounding Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-04-09 09:10 -0700

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