Re: FAQ list update: Q1.1: choosing types

From	Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups	comp.lang.c
Subject	Re: FAQ list update: Q1.1: choosing types
Date	2023-02-15 11:32 -0800
Organization	None to speak of
Message-ID	<87a61erag6.fsf@nosuchdomain.example.com> (permalink)
References	(2 earlier) <87ttzoq943.fsf@nosuchdomain.example.com> <fb2a9938-72f1-438b-95de-ca580431f1e3n@googlegroups.com> <87pmaarden.fsf@nosuchdomain.example.com> <4803956e-d074-4787-b063-ed0593ca949cn@googlegroups.com> <87lekyrb4z.fsf@nosuchdomain.example.com>

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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
> Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
>> On Wednesday, 15 February 2023 at 18:29:07 UTC, Keith Thompson wrote:
> [...]
>>> The name "ssize_t_is_compatible_with_size_t" is a bit misleading. 
>>> C type compatibility is defined very narrowly. A signed type is 
>>> never *compatible* with an unsigned type. What is "compatible" 
>>> supposed to mean in this context?
>>> 
>> It means that the binary representation of the unsigned type is the same
>> as the binary representation of the signed type when it is non-negative.
>>
>> So 
>> ssize_t ssz;
>> size_t sz = sizeof(int);
>> ssz = *(ssize_t *) &sz;
>>
>> puts sizeof(int) into ssz;
>
> That's not what "compatible" means in C.  I asked what the code John
> Dill posted meant by "compatible".  Are you familiar with that code,
> including parts that haven't been posted?

I think I misread the code.  `sizeof (ssize_t) == sizeof (size_t)` is
the condition being asserted, and `size_t_is_compatible_with_size_t` is
the name associated with that assertion, not something that's defined
elsewhere.

ssize_t and size_t being the same size does not guarantee that the
binary representations are the same for common values.  That's
guaranteed only if they are corresponding signed and unsigned types,
like long and unsigned long.  Their representations are very likely to
match, but unless the code does some odd low-level stuff that's unlikely
to matter.

-- 
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 */

Thread

FAQ list update: Q1.1: choosing types scs@eskimo.com (Steve Summit) - 2023-02-13 15:18 +0000
  Re: FAQ list update: Q1.1: choosing types Anton Shepelev <anton.txt@g{oogle}mail.com> - 2023-02-13 18:27 +0300
  Re: FAQ list update: Q1.1: choosing types scott@slp53.sl.home (Scott Lurndal) - 2023-02-13 16:27 +0000
    Re: FAQ list update: Q1.1: choosing types Oğuz <oguzismailuysal@gmail.com> - 2023-02-14 08:55 +0300
  Re: FAQ list update: Q1.1: choosing types Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2023-02-13 18:07 +0000
  Re: FAQ list update: Q1.1: choosing types Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-02-13 10:48 -0800
  Re: FAQ list update: Q1.1: choosing types Kaz Kylheku <864-117-4973@kylheku.com> - 2023-02-14 03:10 +0000
    Re: FAQ list update: Q1.1: choosing types Blue-Maned_Hawk <bluemanedhawk@gmail.com> - 2023-02-14 17:33 -0500
  Re: FAQ list update: Q1.1: choosing types Öö Tiib <ootiib@hot.ee> - 2023-02-13 23:24 -0800
  Re: FAQ list update: Q1.1: choosing types bart c <bart4858@gmail.com> - 2023-02-14 06:22 -0800
    Re: FAQ list update: Q1.1: choosing types Blue-Maned_Hawk <bluemanedhawk@gmail.com> - 2023-02-14 17:48 -0500
  Re: FAQ list update: Q1.1: choosing types John Dill <jadill33@gmail.com> - 2023-02-14 08:17 -0800
    Re: FAQ list update: Q1.1: choosing types Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-02-14 12:34 -0800
      Re: FAQ list update: Q1.1: choosing types John Dill <jadill33@gmail.com> - 2023-02-15 10:04 -0800
        Re: FAQ list update: Q1.1: choosing types Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-02-15 10:28 -0800
          Re: FAQ list update: Q1.1: choosing types Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-02-15 10:57 -0800
            Re: FAQ list update: Q1.1: choosing types Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-02-15 11:17 -0800
              Re: FAQ list update: Q1.1: choosing types Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-02-15 11:32 -0800
          Re: FAQ list update: Q1.1: choosing types John Dill <jadill33@gmail.com> - 2023-02-15 11:01 -0800
            Re: FAQ list update: Q1.1: choosing types Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-02-15 11:28 -0800
              Re: FAQ list update: Q1.1: choosing types John Dill <jadill33@gmail.com> - 2023-02-15 14:00 -0800
  Re: FAQ list update: Q1.1: choosing types Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-02-15 02:54 -0800
  Re: FAQ list update: Q1.1: choosing types Anton Shepelev <anton.txt@g{oogle}mail.com> - 2023-02-15 14:43 +0300
  Re: FAQ list update: Q1.1: choosing types David Brown <david.brown@hesbynett.no> - 2023-02-15 13:55 +0100
    Re: FAQ list update: Q1.1: choosing types Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-02-15 05:31 -0800

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