Re: Nice way of allocating flexible struct.

From	Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups	comp.lang.c
Subject	Re: Nice way of allocating flexible struct.
Date	2025-12-14 22:48 -0800
Organization	A noiseless patient Spider
Message-ID	<86jyyouto5.fsf@linuxsc.com> (permalink)
References	<20251007233002.852@kylheku.com>

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Kaz Kylheku <643-408-1753@kylheku.com> writes:

> Jonas Lund of https://whizzter.woorlic.org/ mentioned this
> trick in a HackerNews comment:
>
> Given:
>
>   struct S {
>     // ...
>     T A[];
>   };
>
> Don't do this:
>
>   malloc(offsetof(S, A) + n * sizeof (T));
>
> But rather this:
>
>   malloc(offsetof(S, A[n]));
>
> It's easy to forget that the second argument of offsetof is a
> designator, not simply a member name.

Clever but inadvisable.  Even if the offsetof() expression compiles,
in most cases it either gives a value that is too small or is
undefined behavior.

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Nice way of allocating flexible struct. Kaz Kylheku <643-408-1753@kylheku.com> - 2025-10-08 06:35 +0000
  Re: Nice way of allocating flexible struct. pozz <pozzugno@gmail.com> - 2025-10-08 09:09 +0200
    Re: Nice way of allocating flexible struct. richard@cogsci.ed.ac.uk (Richard Tobin) - 2025-10-08 12:01 +0000
    Re: Nice way of allocating flexible struct. Kaz Kylheku <643-408-1753@kylheku.com> - 2025-10-08 15:23 +0000
      Re: Nice way of allocating flexible struct. Michael S <already5chosen@yahoo.com> - 2025-10-08 19:04 +0300
        Re: Nice way of allocating flexible struct. Kaz Kylheku <643-408-1753@kylheku.com> - 2025-10-08 20:05 +0000
    Re: Nice way of allocating flexible struct. Michael S <already5chosen@yahoo.com> - 2025-10-08 18:52 +0300
    Re: Nice way of allocating flexible struct. Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-12-14 23:55 -0800
  Re: Nice way of allocating flexible struct. Bonita Montero <Bonita.Montero@gmail.com> - 2025-10-08 11:09 +0200
    Re: Nice way of allocating flexible struct. Bonita Montero <Bonita.Montero@gmail.com> - 2025-10-08 11:23 +0200
      Re: Nice way of allocating flexible struct. Michael S <already5chosen@yahoo.com> - 2025-10-08 12:53 +0300
        Re: Nice way of allocating flexible struct. Bonita Montero <Bonita.Montero@gmail.com> - 2025-10-08 12:09 +0200
          Re: Nice way of allocating flexible struct. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-08 15:59 +0200
            Re: Nice way of allocating flexible struct. BGB <cr88192@gmail.com> - 2025-10-08 12:29 -0500
              Re: Nice way of allocating flexible struct. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-08 21:04 +0200
                Re: Nice way of allocating flexible struct. BGB <cr88192@gmail.com> - 2025-10-08 22:49 -0500
                Re: Nice way of allocating flexible struct. bart <bc@freeuk.com> - 2025-10-10 01:13 +0100
                Re: Nice way of allocating flexible struct. Kaz Kylheku <643-408-1753@kylheku.com> - 2025-10-10 01:54 +0000
                Re: Nice way of allocating flexible struct. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-10-09 19:43 -0700
                Re: Nice way of allocating flexible struct. bart <bc@freeuk.com> - 2025-10-10 11:25 +0100
                Re: Nice way of allocating flexible struct. BGB <cr88192@gmail.com> - 2025-10-09 22:50 -0500
                Re: Nice way of allocating flexible struct. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-10-09 20:59 -0700
                Re: Nice way of allocating flexible struct. BGB <cr88192@gmail.com> - 2025-10-10 01:27 -0500
                Re: Nice way of allocating flexible struct. David Brown <david.brown@hesbynett.no> - 2025-10-10 12:06 +0200
                Re: Nice way of allocating flexible struct. Michael S <already5chosen@yahoo.com> - 2025-10-10 17:28 +0300
                Re: Nice way of allocating flexible struct. David Brown <david.brown@hesbynett.no> - 2025-10-10 17:47 +0200
                Re: Nice way of allocating flexible struct. BGB <cr88192@gmail.com> - 2025-10-10 16:32 -0500
                Re: Nice way of allocating flexible struct. Kaz Kylheku <643-408-1753@kylheku.com> - 2025-10-11 00:02 +0000
                Re: Nice way of allocating flexible struct. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-13 06:20 +0200
                Re: Nice way of allocating flexible struct. BGB <cr88192@gmail.com> - 2025-10-10 15:01 -0500
                Re: Nice way of allocating flexible struct. Kaz Kylheku <643-408-1753@kylheku.com> - 2025-10-10 23:45 +0000
                Re: Nice way of allocating flexible struct. Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-06 18:24 -0800
                Re: Nice way of allocating flexible struct. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-14 06:29 +0200
                Re: Nice way of allocating flexible struct. BGB <cr88192@gmail.com> - 2025-10-14 20:13 -0500
                Re: Nice way of allocating flexible struct. bart <bc@freeuk.com> - 2025-10-15 11:26 +0100
                Re: Nice way of allocating flexible struct. BGB <cr88192@gmail.com> - 2025-10-15 13:00 -0500
                Re: Nice way of allocating flexible struct. bart <bc@freeuk.com> - 2025-10-17 22:07 +0100
                Re: Nice way of allocating flexible struct. BGB <cr88192@gmail.com> - 2025-10-17 17:44 -0500
                Re: Nice way of allocating flexible struct. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-20 10:02 +0200
                Re: Nice way of allocating flexible struct. BGB <cr88192@gmail.com> - 2025-10-20 04:42 -0500
                Re: Nice way of allocating flexible struct. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-21 03:40 +0200
                Re: Nice way of allocating flexible struct. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-16 06:45 +0200
                Re: Nice way of allocating flexible struct. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-16 06:37 +0200
                Re: Nice way of allocating flexible struct. BGB <cr88192@gmail.com> - 2025-10-16 04:43 -0500
                Re: Nice way of allocating flexible struct. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-20 09:58 +0200
                Re: Nice way of allocating flexible struct. rbowman <bowman@montana.com> - 2025-10-20 18:36 +0000
                Re: Nice way of allocating flexible struct. BGB <cr88192@gmail.com> - 2025-10-20 16:44 -0500
                Re: Nice way of allocating flexible struct. rbowman <bowman@montana.com> - 2025-10-21 01:33 +0000
                Language-design, tradeoffs (was Re: Nice way of allocating flexible struct.) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-21 04:19 +0200
                Re: Language-design, tradeoffs (was Re: Nice way of allocating flexible struct.) BGB <cr88192@gmail.com> - 2025-10-21 04:27 -0500
                Re: Language-design, tradeoffs (was Re: Nice way of allocating flexible struct.) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-22 02:30 +0200
                Re: Language-design, tradeoffs (was Re: Nice way of allocating flexible struct.) BGB <cr88192@gmail.com> - 2025-10-22 02:10 -0500
                Re: Nice way of allocating flexible struct. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-21 03:51 +0200
                Re: Nice way of allocating flexible struct. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-10-20 19:21 -0700
                Re: Nice way of allocating flexible struct. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-21 04:53 +0200
                Re: Nice way of allocating flexible struct. rbowman <bowman@montana.com> - 2025-10-21 18:21 +0000
                Re: Nice way of allocating flexible struct. BGB <cr88192@gmail.com> - 2025-10-21 13:42 -0500
                Re: Nice way of allocating flexible struct. James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-10-21 06:17 -0400
                Re: Nice way of allocating flexible struct. rbowman <bowman@montana.com> - 2025-10-21 18:41 +0000
                Re: Nice way of allocating flexible struct. rbowman <bowman@montana.com> - 2025-10-21 18:12 +0000
            Re: Nice way of allocating flexible struct. Bonita Montero <Bonita.Montero@gmail.com> - 2025-10-08 19:36 +0200
              Re: Nice way of allocating flexible struct. Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2025-10-08 19:51 +0200
    Re: Nice way of allocating flexible struct. Kaz Kylheku <643-408-1753@kylheku.com> - 2025-10-08 15:29 +0000
  Re: Nice way of allocating flexible struct. BGB <cr88192@gmail.com> - 2025-10-08 11:33 -0500
    Re: Nice way of allocating flexible struct. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-10-08 14:57 -0700
      Re: Nice way of allocating flexible struct. Kaz Kylheku <643-408-1753@kylheku.com> - 2025-10-09 01:39 +0000
        Re: Nice way of allocating flexible struct. BGB <cr88192@gmail.com> - 2025-10-08 22:25 -0500
          Re: Nice way of allocating flexible struct. Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2025-10-09 19:50 -0700
            Re: Nice way of allocating flexible struct. Kaz Kylheku <643-408-1753@kylheku.com> - 2025-10-10 04:20 +0000
      Re: Nice way of allocating flexible struct. Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-12-15 11:24 -0800
  Re: Nice way of allocating flexible struct. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-10-08 13:35 -0700
    Re: Nice way of allocating flexible struct. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-10-08 13:36 -0700
  Re: Nice way of allocating flexible struct. Tim Rentsch <tr.17687@z991.linuxsc.com> - 2025-12-14 22:48 -0800

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