From: Chris Lattner <sabre@nondot.org>
To: Tiago Stein <tiago@lisha.ufsc.br>
Cc: gcc@gcc.gnu.org
Subject: RE: Double abstract class Inheritance concern.
Date: Mon, 29 Mar 2004 14:03:00 -0000 [thread overview]
Message-ID: <Pine.LNX.4.44.0403281937360.23968-100000@nondot.org> (raw)
Tiago Stein wrote:
> class A{};
> class B :public A{};
> class C: public A{ int g; };
> class D: public B, public C {
> unsigned int foo;
> };
> Why sizeof class D is 12? Should not be 8?
I believe the reason is that the ABI does not permit multiple different
instances of A to be located at the same address, even if they have zero
size. If the size of the structure was 8, all of "A", "B", and "A" would
have offset zero.
I'm not sure WHY this is required, but this is the reason it happens at
least. A declaration of "A X[100];" allocates 100 bytes as
a result of the same rule.
-Chris
--
http://llvm.cs.uiuc.edu/
http://www.nondot.org/~sabre/Projects/
next reply other threads:[~2004-03-29 1:39 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-03-29 14:03 Chris Lattner [this message]
2004-03-29 17:16 ` Nathan Sidwell
2004-03-29 18:49 ` Joe Buck
-- strict thread matches above, loose matches on Subject: below --
2004-03-29 13:57 Tiago Stein
2004-03-29 15:15 ` Alexandre Oliva
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