Date: Thu, 20 Feb 2025 12:03:39 +0100 From: Michael Gmelin <grembo@freebsd.org> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: current@freebsd.org Subject: Re: Empty structures have sizeof(1) in C++ now ? Message-ID: <20250220120339.2f1af442.grembo@freebsd.org> In-Reply-To: <202502200940.51K9eswS003142@critter.freebsd.dk>
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On Thu, 20 Feb 2025 09:40:54 +0000
Poul-Henning Kamp <phk@phk.freebsd.dk> wrote:
> Is this a bug ?
>
>
> critter phk> cat /tmp/_.c
>
> #include <stdio.h>
> struct foo {
> };
>
> int
> main(int argc, char **argv)
> {
> struct foo bar;
> printf("%jd %jd\n", sizeof(struct foo), sizeof(bar));
> return (0);
> }
> critter phk> cc -o /tmp/a.out /tmp/_.c
> critter phk> /tmp/a.out
> 0 0
> critter phk> c++ -o /tmp/a.out /tmp/_.c
> c++: warning: treating 'c' input as 'c++' when in C++ mode,
> this behavior is deprecated [-Wdeprecated] critter phk> /tmp/a.out
> 1 1
>
AFAIK it has always been like that, see
https://www.stroustrup.com/bs_faq2.html#sizeof-empty :
To ensure that the addresses of two different objects will be
different. For the same reason, "new" always returns pointers to
distinct objects.
-m
--
Michael Gmelin
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