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Re: #include <stdint.h>

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On 10/6/21 12:35 PM, Andrey Tarasevich wrote:
> On 6/24/2021 11:28 AM, Keith Thompson wrote:
>>
>> My reading of the standard is that that's certainly the intent, but
>> it's not quite stated explicitly.
>>
> 
> Yes, it does. The intent of 6.2.5/9 is, among other things, is to 
> postulate interchangeability of values of corresponding signed-unsigned 
> types as function arguments.


In several locations, the standard says "The same representation and
alignment requirements are meant to imply interchangeability as
arguments to functions, return values from functions, and members of
unions."

There's several problems with that statement. Firstly, "are meant to
imply" is weasel-wording. It could have said, more simply and
forcefully, "implies". Secondly, the implication doesn't hold up under
close examination. For instance, unsigned and signed arguments with the
same alignment and same representation for positive values of the signed
type could still be passed by different methods as arguments or return
values, which would prevent them from being interchangeable. Finally,
that wording only appears in informative footnotes, not in normative text.

After raising this issue many times over a couple of decades, I finally
got confirmation from Larry Jones in 2011 (at that time, secretary of
the committee) that use of "are meant to imply" rather than "implies"
was deliberate, because it was in fact understood that no such
implication was correct. He also confirmed that the non-normative nature
of that text was also deliberate - the committee did NOT want to mandate
that the types be interchangeable, only to recommend that they be made
interchangeable.

> No special remarks of any kind are made about variadic functions, which 
> immediately closes the matter. No need to dig deeper and involve 
> `va_arg` or anything else.

In C2011, the descriptions of the printf() and scanf() family of
functions contained one notable difference from the corresponding
general requirements for functions with variable arguments:  "If any
argument is not the correct type for the corresponding conversion
specification, the behavior is undefined.".

An implementation of C2011 could therefore have provided a conforming
extension to the <va_args.h> facilities, allowing you to determine the
type of the argument corresponding to each parameter,and the
implementations of those functions could make use of that information to
fail in some fashion when the argument's type is not correct. Such an
implementation would not violate any requirement of C2011.

In n2596.pdf, the latest draft of the next version that I have access
to, that wording has been replaced:
"fprintf shall behave as if it uses va_arg with a type argument naming
the type resulting from applying the default argument promotions to the
type corresponding to the conversion specification and then converting
the result of the va_arg expansion to the type corresponding to the
conversion specification."

This indicates that the committee acknowledges the validity of that
complaint, and has resolved it in a way that's not compatible with the
hypothetical implementation I've described above.

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#include <stdint.h> SIMON <invalid@invalid.invalid> - 2021-06-13 23:08 +0100
  Re: #include <stdint.h> Bart <bc@freeuk.com> - 2021-06-13 23:27 +0100
    Re: #include <stdint.h> Bart <bc@freeuk.com> - 2021-06-13 23:57 +0100
      Re: #include <stdint.h> Philipp Klaus Krause <pkk@spth.de> - 2021-06-14 09:03 +0200
        Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-14 01:23 -0700
          Re: #include <stdint.h> Philipp Klaus Krause <pkk@spth.de> - 2021-06-14 12:31 +0200
        Re: #include <stdint.h> Bart <bc@freeuk.com> - 2021-06-14 11:54 +0100
  Re: #include <stdint.h> James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-06-13 18:34 -0400
  Re: #include <stdint.h> Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-06-13 23:34 +0100
  Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-13 17:48 -0700
    Re: #include <stdint.h> Philipp Klaus Krause <pkk@spth.de> - 2021-06-14 09:09 +0200
      Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-14 01:24 -0700
        Re: #include <stdint.h> Philipp Klaus Krause <pkk@spth.de> - 2021-06-14 12:30 +0200
    Re: #include <stdint.h> Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-06-24 10:31 -0700
      Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-24 11:28 -0700
        Re: #include <stdint.h> Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-07-11 02:49 -0700
          Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-07-11 15:30 -0700
            Re: #include <stdint.h> Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-07-16 03:33 -0700
              Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-07-16 12:31 -0700
                Re: #include <stdint.h> Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-09-30 07:07 -0700
                Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-09-30 08:42 -0700
                Re: #include <stdint.h> Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-10-06 03:55 -0700
                Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-06 07:06 -0700
                Re: #include <stdint.h> James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-06 11:47 -0400
        Re: #include <stdint.h> Andrey Tarasevich <andreytarasevich@hotmail.com> - 2021-10-06 09:35 -0700
          Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-10-06 10:06 -0700
          Re: #include <stdint.h> James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-06 17:40 -0400
            Re: #include <stdint.h> Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-06 22:14 +0000
              Re: #include <stdint.h> James Kuyper <jameskuyper@alumni.caltech.edu> - 2021-10-06 20:06 -0400
                Re: #include <stdint.h> Branimir Maksimovic <branimir.maksimovic@icloud.com> - 2021-10-07 02:15 +0000
      Re: #include <stdint.h> Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-06-24 22:34 +0100
        Re: #include <stdint.h> Öö Tiib <ootiib@hot.ee> - 2021-06-24 15:01 -0700
          Re: #include <stdint.h> Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2021-06-24 15:26 -0700
        Re: #include <stdint.h> Tim Rentsch <tr.17687@z991.linuxsc.com> - 2021-07-11 02:14 -0700

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