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Re: structs passed by copy

From Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups comp.lang.c
Subject Re: structs passed by copy
Date 2023-01-23 17:58 -0800
Organization None to speak of
Message-ID <87pmb4elsn.fsf@nosuchdomain.example.com> (permalink)
References (8 earlier) <tqkcal$393b1$1@dont-email.me> <87o7qqglva.fsf@nosuchdomain.example.com> <86fsc0hl4i.fsf@linuxsc.com> <87a628g440.fsf@nosuchdomain.example.com> <tqnbb5$3rjfq$3@dont-email.me>

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James Kuyper <jameskuyper@alumni.caltech.edu> writes:
> On 1/23/23 19:37, Keith Thompson wrote:
>> Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
>>> Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
>>>
>>> [...]
>>>
>>>> BTW, I was wrong about one thing: Support for _Imaginary is optional
>>>> even for an implementation that predefines __STDC_IEC_559_COMPLEX__.
>>>> `#ifdef _Imaginary_I` can be used to detect whether an implementation
>>>> supports imaginary types.
>>>
>>> I don't see how you reach this conclusion. My reading of N1570 says
>>> an implementation that defines __STDC_IEC_559_COMPLEX__ must have
>>> imaginary types. Annex G is normative. It clearly states that an
>>> implementation that defines __STDC_IEC_559_COMPLEX__ must conform to
>>> its specifications. Section G.2 says _Imaginary is a keyword, and
>>> there are three imaginary types, float _Imaginary, double _Imaginary,
>>> and long double _Imaginary. That statement (actually a combination of
>>> two statements in the annex) is a specification, and so any designated
>>> implementation must conform to it.
>>
>> I believe you're correct, and I was wrong (the second time, not
>> the first). I honestly don't know how I reached the conclusion
>> that defining __STDC_IEC_559_COMPLEX__ *doesn't* imply a requirement
>> to support imaginary types. Most likely I read one document while
>> thinking it was a different one.
>
> I think you were on the right track from the beginning.
>
> "The macros imaginary and _Imaginary_I are defined if and only if the
> implementation supports imaginary types." (7.3.1p5)
>
> That pretty clearly indicates that support for imaginary types is
> optional. It wouldn't be needed if imaginary types were guaranteed to be
> supported if complex types are supported.

N1570 6.2.5 (Types) mentions complex types but not imaginary types,
other than in a footnote that refers to Annex G (and that incorrectly
says it's informative, as it was in C99).  That seems like an odd
omission.

N1570 7.3.1 (<complex.h>) makes it clear that imaginary types are
optional (and that the macro I expands to an expression of either
complex or imaginary type, which seems really odd).

6.10.8.1: An implementation may predefine __STDC_NO_COMPLEX__ to
indicate that it doesn't support complex types (new in C11; in C99
complex types were mandatory).

My conclusions:

Support for complex types is optional.

Support for imaginary types is optional.

(Support for imaginary types but not complex types is probably allowed,
but would be silly.)

An implementation may optionally predefine __STDC_IEC_559_COMPLEX__.
Any implementation that does so must support both complex and imaginary
types, and must do so as specified by Annex G.

Recent versions of gcc and clang both predefine __STDC_IEC_559_COMPLEX__,
but neither supports imaginary types (with command-line options that
should make them conform to C11).  This makes them non-conforming.  I
feel like I might be missing something here, because it *seems* like an
obvious non-conformance, and I don't see anything about it on gcc's
bugzilla.

An implementation *could* support complex types, or complex and
imaginary types, without conforming to Annex G, for example if the
target platform doesn't support IEEE floating-point.

-- 
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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structs passed by copy Thiago Adams <thiago.adams@gmail.com> - 2023-01-20 10:41 -0800
  Re: structs passed by copy gazelle@shell.xmission.com (Kenny McCormack) - 2023-01-20 19:01 +0000
    Re: structs passed by copy Anton Shepelev <anton.txt@gmail.com> - 2023-01-20 23:01 +0300
      Re: structs passed by copy gazelle@shell.xmission.com (Kenny McCormack) - 2023-01-20 21:28 +0000
        Re: structs passed by copy Kaz Kylheku <864-117-4973@kylheku.com> - 2023-01-21 09:14 +0000
        Re: structs passed by copy Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2023-01-21 10:58 -0700
          Re: structs passed by copy gazelle@shell.xmission.com (Kenny McCormack) - 2023-01-21 18:00 +0000
          Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-01-21 16:14 -0800
            Re: structs passed by copy James Kuyper <jameskuyper@alumni.caltech.edu> - 2023-01-22 16:00 -0500
              Re: structs passed by copy "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-01-22 13:07 -0800
              Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-01-22 13:27 -0800
                Re: structs passed by copy "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-01-22 13:51 -0800
                Re: structs passed by copy "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-01-22 13:51 -0800
                Re: structs passed by copy James Kuyper <jameskuyper@alumni.caltech.edu> - 2023-01-22 17:11 -0500
                Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-01-22 16:01 -0800
                Re: structs passed by copy Richard Damon <Richard@Damon-Family.org> - 2023-01-22 21:22 -0500
                Re: structs passed by copy David Brown <david.brown@hesbynett.no> - 2023-01-23 10:46 +0100
                Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-01-23 12:15 -0800
                Re: structs passed by copy David Brown <david.brown@hesbynett.no> - 2023-01-23 21:47 +0100
                Re: structs passed by copy Michael S <already5chosen@yahoo.com> - 2023-01-23 13:21 -0800
                Re: structs passed by copy Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-01-23 23:49 +0000
                Re: structs passed by copy Michael S <already5chosen@yahoo.com> - 2023-01-24 02:46 -0800
                Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-24 04:18 -0800
                Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-24 04:45 -0800
                Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-24 04:54 -0800
                Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-24 05:26 -0800
                Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-24 05:38 -0800
                Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-24 05:53 -0800
                Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-24 06:20 -0800
                Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-24 06:56 -0800
                Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-24 07:17 -0800
                Re: structs passed by copy Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-01-24 12:56 +0000
                Re: structs passed by copy Michael S <already5chosen@yahoo.com> - 2023-01-24 07:29 -0800
                Re: structs passed by copy Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-01-23 15:44 -0800
                Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-01-23 16:37 -0800
                Re: structs passed by copy James Kuyper <jameskuyper@alumni.caltech.edu> - 2023-01-23 20:13 -0500
                Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-01-23 17:58 -0800
                Re: structs passed by copy Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-01-24 07:53 -0800
                Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-01-24 11:14 -0800
                Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-01-24 12:02 -0800
                Re: structs passed by copy Phil Carmody <pc+usenet@asdf.org> - 2023-01-25 10:18 +0200
                Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-01-25 10:53 -0800
                Re: structs passed by copy Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-01-29 13:30 -0800
                Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-01-29 17:42 -0800
                Re: structs passed by copy Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-02-17 07:19 -0800
                Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-02-17 09:35 -0800
                Re: structs passed by copy John Forkosh <forkosh@panix.com> - 2023-01-30 04:24 +0000
                Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-01-29 21:10 -0800
                Re: structs passed by copy Michael S <already5chosen@yahoo.com> - 2023-01-30 13:55 -0800
                Re: structs passed by copy Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-02-17 05:57 -0800
      Re: structs passed by copy James Kuyper <jameskuyper@alumni.caltech.edu> - 2023-01-21 05:00 -0500
        Re: structs passed by copy Anton Shepelev <anton.txt@gmail.com> - 2023-01-21 23:00 +0300
          Re: structs passed by copy Richard Damon <Richard@Damon-Family.org> - 2023-01-21 17:10 -0500
    Re: structs passed by copy Thiago Adams <thiago.adams@gmail.com> - 2023-01-20 18:12 -0800
    Re: structs passed by copy antispam@math.uni.wroc.pl - 2023-01-21 02:28 +0000
  Re: structs passed by copy Blue-Maned_Hawk <bluemanedhawk@gmail.com> - 2023-01-20 14:09 -0500
    Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-01-20 11:26 -0800
  Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-01-20 11:22 -0800
  Re: structs passed by copy Bart <bc@freeuk.com> - 2023-01-20 20:16 +0000
    Re: structs passed by copy Thiago Adams <thiago.adams@gmail.com> - 2023-01-20 19:16 -0800
      Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-01-20 21:08 -0800
      Re: structs passed by copy Bart <bc@freeuk.com> - 2023-01-21 13:30 +0000
        Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-22 10:27 -0800
  Re: structs passed by copy Richard Damon <Richard@Damon-Family.org> - 2023-01-20 21:35 -0500
  Re: structs passed by copy "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-01-20 19:01 -0800
    Re: structs passed by copy "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-01-21 17:01 -0800
  Re: structs passed by copy David Brown <david.brown@hesbynett.no> - 2023-01-21 14:59 +0100
  Re: structs passed by copy Opus <ifonly@youknew.org> - 2023-01-21 19:59 +0100
  Re: structs passed by copy Michael S <already5chosen@yahoo.com> - 2023-01-21 16:55 -0800
    Re: structs passed by copy Thiago Adams <thiago.adams@gmail.com> - 2023-01-22 02:32 -0800
      Re: structs passed by copy Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-01-22 15:54 +0000
        Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-22 09:17 -0800
          Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-22 09:56 -0800
            Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-22 10:19 -0800
              Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-22 11:01 -0800
                Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-22 11:08 -0800
                Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-22 11:17 -0800
                Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-01-22 13:27 -0800
        Re: structs passed by copy "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-01-22 13:04 -0800
          Re: structs passed by copy Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-01-22 21:43 +0000
            Re: structs passed by copy "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-01-22 14:10 -0800
              Re: structs passed by copy Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-01-22 22:29 +0000
                Re: structs passed by copy "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-01-22 14:39 -0800
                Re: structs passed by copy Thiago Adams <thiago.adams@gmail.com> - 2023-01-22 19:06 -0800
                Re: structs passed by copy David Brown <david.brown@hesbynett.no> - 2023-01-23 10:54 +0100
        Re: structs passed by copy Thiago Adams <thiago.adams@gmail.com> - 2023-01-22 19:00 -0800
          Re: structs passed by copy Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-01-23 12:14 +0000
  Re: structs passed by copy Jorgen Grahn <grahn+nntp@snipabacken.se> - 2023-02-11 19:35 +0000
    Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-02-11 15:08 -0800
      Re: structs passed by copy Öö Tiib <ootiib@hot.ee> - 2023-02-11 15:56 -0800
        Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-02-11 16:32 -0800
          Re: structs passed by copy James Kuyper <jameskuyper@alumni.caltech.edu> - 2023-02-12 01:23 -0500
            Re: structs passed by copy David Brown <david.brown@hesbynett.no> - 2023-02-12 11:24 +0100
              Re: structs passed by copy Vir Campestris <vir.campestris@invalid.invalid> - 2023-02-12 22:11 +0000
                Re: structs passed by copy David Brown <david.brown@hesbynett.no> - 2023-02-13 10:25 +0100
                Re: structs passed by copy Thiago Adams <thiago.adams@gmail.com> - 2023-02-13 06:41 -0800
                Re: structs passed by copy Thiago Adams <thiago.adams@gmail.com> - 2023-02-13 06:50 -0800
                Re: structs passed by copy David Brown <david.brown@hesbynett.no> - 2023-02-13 17:22 +0100
                Re: structs passed by copy Thiago Adams <thiago.adams@gmail.com> - 2023-02-13 10:47 -0800
                Re: structs passed by copy David Brown <david.brown@hesbynett.no> - 2023-02-13 21:50 +0100
                Re: structs passed by copy bart c <bart4858@gmail.com> - 2023-02-15 17:14 -0800
                Re: structs passed by copy David Brown <david.brown@hesbynett.no> - 2023-02-16 10:53 +0100
                Re: structs passed by copy scott@slp53.sl.home (Scott Lurndal) - 2023-02-16 15:22 +0000
            Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-02-12 11:04 -0800
          Re: structs passed by copy Öö Tiib <ootiib@hot.ee> - 2023-02-12 12:41 -0800
          Re: structs passed by copy Andrey Tarasevich <andreytarasevich@hotmail.com> - 2023-02-16 22:49 -0800
      Re: structs passed by copy "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-02-11 17:49 -0800
      Grammar nitpick (Was: structs passed by copy) gazelle@shell.xmission.com (Kenny McCormack) - 2023-02-12 06:30 +0000
      Re: structs passed by copy Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-03-06 09:32 -0800
        Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-03-06 09:58 -0800
          Re: structs passed by copy Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-03-06 11:30 -0800
            Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-03-06 12:59 -0800
    Re: structs passed by copy Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-02-15 01:52 -0800
      Re: structs passed by copy Thiago Adams <thiago.adams@gmail.com> - 2023-02-16 05:20 -0800
        Re: structs passed by copy David Brown <david.brown@hesbynett.no> - 2023-02-16 16:49 +0100
        Re: structs passed by copy Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-02-26 08:12 -0800
          Re: structs passed by copy Thiago Adams <thiago.adams@gmail.com> - 2023-02-28 05:38 -0800
            Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-02-28 14:18 -0800
              Re: structs passed by copy Thiago Adams <thiago.adams@gmail.com> - 2023-03-01 05:02 -0800
                Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-03-01 10:23 -0800
                Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-03-01 10:42 -0800
                Re: structs passed by copy bart c <bart4858@gmail.com> - 2023-03-01 15:13 -0800
                Re: structs passed by copy Thiago Adams <thiago.adams@gmail.com> - 2023-03-02 04:17 -0800
                Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-03-05 04:17 -0800
                Re: structs passed by copy fir <profesor.fir@gmail.com> - 2023-03-05 04:55 -0800
                Re: structs passed by copy David Brown <david.brown@hesbynett.no> - 2023-03-02 10:48 +0100
                Re: structs passed by copy Thiago Adams <thiago.adams@gmail.com> - 2023-03-02 04:07 -0800
                Re: structs passed by copy David Brown <david.brown@hesbynett.no> - 2023-03-02 15:08 +0100
                Re: structs passed by copy Thiago Adams <thiago.adams@gmail.com> - 2023-03-02 09:22 -0800
              Re: structs passed by copy gazelle@shell.xmission.com (Kenny McCormack) - 2023-03-01 13:34 +0000
                Re: structs passed by copy Richard Damon <Richard@Damon-Family.org> - 2023-03-01 21:42 -0500
            Re: structs passed by copy Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-03-06 09:36 -0800
  Re: structs passed by copy Maciej Zelma <maciej.projectmanager@gmail.com> - 2023-02-17 14:10 -0800
    Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-02-17 15:45 -0800
      Re: structs passed by copy scott@slp53.sl.home (Scott Lurndal) - 2023-02-18 00:12 +0000
        Re: structs passed by copy bart c <bart4858@gmail.com> - 2023-02-18 02:33 -0800
    Re: structs passed by copy James Kuyper <jameskuyper@alumni.caltech.edu> - 2023-02-18 00:44 -0500
      Re: structs passed by copy Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-02-17 22:21 -0800
  Re: structs passed by copy Bonita Montero <Bonita.Montero@gmail.com> - 2023-03-01 18:00 +0100
    Re: structs passed by copy Thiago Adams <thiago.adams@gmail.com> - 2023-03-01 09:18 -0800
      Re: structs passed by copy Bonita Montero <Bonita.Montero@gmail.com> - 2023-03-05 14:05 +0100

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