Date: Wed, 21 Feb 2001 10:22:00 -0600 From: "Jacques A. Vidrine" <n@nectar.com> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: Warner Losh <imp@village.org>, freebsd-hackers@FreeBSD.ORG Subject: Re: portability sanity check Message-ID: <20010221102200.A93525@hamlet.nectar.com> In-Reply-To: <2056.982772015@critter>; from phk@critter.freebsd.dk on Wed, Feb 21, 2001 at 05:13:35PM %2B0100 References: <200102211553.f1LFrvs07412@billy-club.village.org> <2056.982772015@critter>
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On Wed, Feb 21, 2001 at 05:13:35PM +0100, Poul-Henning Kamp wrote:
> In message <200102211553.f1LFrvs07412@billy-club.village.org>, Warner Losh writes:
> >In message <20010221094228.A93221@hamlet.nectar.com> "Jacques A. Vidrine" writes:
> >: Likewise if the first member were a more complex data type, but
> >: nevertheless the same between the different structures.
> >:
> >: It seems safe to me, but I can't explain why :-)
> >
> >It is obfuscated 'C', but it is safe. The standard requires that
> >(void *) &foo == (void *) &foo->s and that if s were a complex
> >structure that it be laid out the same in all instances of s. So I
> >think that it is "safe" to do that.
>
> Safe, but stupid, since type-safety is lost when doing so.
Type-safety is a cruch for the weak-minded.
:-)
But seriously I think that for the purpose of building a utility
function for use by qsort or similar, using a union just for such
a purpose is more obfuscated.
struct nothing_much_in_common_really {
const char *s;
union {
struct foo foo;
struct bar bar;
} u;
};
But if there is a better way, I'm all ears :-)
Cheers,
--
Jacques Vidrine / n@nectar.com / jvidrine@verio.net / nectar@FreeBSD.org
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