Path: utzoo!attcan!uunet!lll-winken!sun-barr!cs.utexas.edu!milano!cadillac!vaughan@mcc.com
From: vaughan@mcc.com (Paul Vaughan)
Newsgroups: comp.lang.c++
Subject: Re: Multiple inheritance with virtual bases
Message-ID: <12342@cadillac.CAD.MCC.COM>
Date: 22 Oct 90 15:44:23 GMT
References: <1990Oct21.211143.3459@nowhere.uucp>
Sender: news@cadillac.CAD.MCC.COM
Reply-To: vaughan@mcc.com (Paul Vaughan)
Organization: MCC VLSI CAD Program
Lines: 42
In-reply-to: sking@nowhere.uucp (Steven King)


The discussion between Kazuyuki Hagiwara and Steven King about the
sizes of muliply and virtually derived objects is curious indeed.
Here is what GNU C++ does, followed by cfront 2.0 (Sun C++).

#include <stream.h>

struct A {
	char		avar0[1000];
};

struct B : virtual public A {
	int		bvar;
};

struct C : virtual public A {
	int		cvar;
};

struct D : virtual public B, virtual public C {
	int		dvar;
};

main() {
  cout << "A " << sizeof(A) 
    << " B " << sizeof(B) 
      << " C " << sizeof(C) 
	<< " D " << sizeof(D) << "\n";
}

bash$ g++  -o trash trash.cc
bash$ trash
A 1000 B 1008 C 1008 D 1028                            <= reasonable
bash$ CC  -o trash trash.cc
CC  trash.cc:
cc   -o /d2/prism/prism/src/sim/src/trash -I/net/sunspot/usr/cadsw/CC/sun4/incl  trash.c  -L/net/sunspot/usr/cadsw/CC/sun4/ -lC
bash$ trash
A 1000 B 1008 C 1008 D 2032                            <= unreasonable


 Paul Vaughan, MCC CAD Program | ARPA: vaughan@mcc.com | Phone: [512] 338-3639
 Box 200195, Austin, TX 78720  | UUCP: ...!cs.utexas.edu!milano!cadillac!vaughan