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Re: allocating two objects in one malloc

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Lew Pitcher <lew.pitcher@digitalfreehold.ca> writes:
> On March 24, 2020 11:11, James Kuyper wrote:
>> On Wednesday, March 18, 2020 at 7:48:47 PM UTC-4, Thiago Adams wrote:
>> ...
>>> Something I  have considered to suggest for the C language
>>> is make the operator [] available for empty arrays at the end.
>>> 
>>> 
>>> struct array
>>> {
>>>   int size;
>>>   int capacity;
>>>   char data[];
>>> };
>> 
>> You're 21 years late - flexible array members were added in C99.
> [snip]
>
> To me, this seems to be a re-implementation of a pattern seen in 40-year-old 
> programs written to the K&R standard.

Yes, that's exactly what it is.

The old pattern is called the "struct hack".  It worked as expected with
more or all compilers, but strictly speaking it had (and still has)
undefined behavior.  Quoting the C99 Rationale:

    The Committee felt that, although there was no way to
    implement the “struct hack” in C89, it was nonetheless a
    useful facility. Therefore the new feature of “flexible array
    members” was introduced. Apart from the empty brackets, and the
    removal of the “-1” in the malloc call, this is used in the
    same way as the struct hack, but is now explicitly valid code.

See also question 2.6 of the comp.lang.c FAQ <http://www.c-faq.com/>.

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

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allocating two objects in one malloc Thiago Adams <thiago.adams@gmail.com> - 2020-03-18 10:14 -0700
  Re: allocating two objects in one malloc Bonita Montero <Bonita.Montero@gmail.com> - 2020-03-18 18:17 +0100
    Re: allocating two objects in one malloc Thiago Adams <thiago.adams@gmail.com> - 2020-03-18 10:55 -0700
      Re: allocating two objects in one malloc Thiago Adams <thiago.adams@gmail.com> - 2020-03-18 11:01 -0700
      Re: allocating two objects in one malloc felix@palmen-it.de (Felix Palmen) - 2020-03-18 19:14 +0100
        Re: allocating two objects in one malloc Thiago Adams <thiago.adams@gmail.com> - 2020-03-18 11:35 -0700
          Re: allocating two objects in one malloc felix@palmen-it.de (Felix Palmen) - 2020-03-18 19:44 +0100
            Re: allocating two objects in one malloc Thiago Adams <thiago.adams@gmail.com> - 2020-03-18 12:07 -0700
              Re: allocating two objects in one malloc Bart <bc@freeuk.com> - 2020-03-18 20:39 +0000
                Re: allocating two objects in one malloc Thiago Adams <thiago.adams@gmail.com> - 2020-03-18 13:52 -0700
              Re: allocating two objects in one malloc felix@palmen-it.de (Felix Palmen) - 2020-03-18 23:11 +0100
                Re: allocating two objects in one malloc Thiago Adams <thiago.adams@gmail.com> - 2020-03-18 16:48 -0700
                Re: allocating two objects in one malloc Bart <bc@freeuk.com> - 2020-03-19 01:16 +0000
                Re: allocating two objects in one malloc Thiago Adams <thiago.adams@gmail.com> - 2020-03-24 06:11 -0700
                Re: allocating two objects in one malloc Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-24 14:49 +0000
                Re: allocating two objects in one malloc Thiago Adams <thiago.adams@gmail.com> - 2020-03-24 08:46 -0700
                Re: allocating two objects in one malloc James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-03-24 07:50 -0700
                Re: allocating two objects in one malloc Thiago Adams <thiago.adams@gmail.com> - 2020-03-24 08:48 -0700
                Re: allocating two objects in one malloc chad <cdalten@gmail.com> - 2020-03-19 05:15 -0700
                Re: allocating two objects in one malloc James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-03-24 08:11 -0700
                Re: allocating two objects in one malloc Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-03-24 11:35 -0400
                Re: allocating two objects in one malloc Richard Damon <Richard@Damon-Family.org> - 2020-03-24 13:50 -0400
                Re: allocating two objects in one malloc Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-24 20:58 +0000
                Re: allocating two objects in one malloc Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-03-24 13:10 -0700
                Re: allocating two objects in one malloc Thiago Adams <thiago.adams@gmail.com> - 2020-03-24 08:52 -0700
                Re: allocating two objects in one malloc Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-03-24 13:05 -0700
          Re: allocating two objects in one malloc Bonita Montero <Bonita.Montero@gmail.com> - 2020-03-18 19:53 +0100
          Re: allocating two objects in one malloc Bart <bc@freeuk.com> - 2020-03-18 20:29 +0000
          Re: allocating two objects in one malloc jadill33@gmail.com - 2020-03-18 13:44 -0700
          Re: allocating two objects in one malloc Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-03-18 21:00 +0000
  Re: allocating two objects in one malloc Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-03-18 10:18 -0700
  Re: allocating two objects in one malloc felix@palmen-it.de (Felix Palmen) - 2020-03-18 18:43 +0100
    Re: allocating two objects in one malloc Bonita Montero <Bonita.Montero@gmail.com> - 2020-03-18 18:55 +0100
      Re: allocating two objects in one malloc Thiago Adams <thiago.adams@gmail.com> - 2020-03-18 10:56 -0700
        Re: allocating two objects in one malloc Bonita Montero <Bonita.Montero@gmail.com> - 2020-03-18 19:06 +0100
      Re: allocating two objects in one malloc felix@palmen-it.de (Felix Palmen) - 2020-03-18 19:01 +0100
    Re: allocating two objects in one malloc James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-03-18 14:21 -0400
      Re: allocating two objects in one malloc felix@palmen-it.de (Felix Palmen) - 2020-03-18 19:30 +0100
        Re: allocating two objects in one malloc James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-03-18 15:08 -0400

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