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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: Nice way of allocating flexible struct.
Date: Sun, 14 Dec 2025 22:48:42 -0800
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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.