Re: [boost] bug in type_traits/is_virtual_base_of ??

Subject: Re: [boost] bug in type_traits/is_virtual_base_of ??
From: Daniel Larimer (dlarimer_at_[hidden])
Date: 2010-02-11 13:36:35

I included the compiler version in the first post, but here it is again.  I have expanded upon the bug and provided the actual output of the code.  Looking at the implementation of is_virtual_base_of<>, it appears that it makes some assumptions regarding the sizeof() a class with and without virtual inheritance that are perhaps invalid?  

i686-apple-darwin10-g++-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5646) (dot 1)

#include <stdio.h>
#include <boost/type_traits/is_virtual_base_of.hpp>

struct A
{
    int x;
};
struct B
{
    int y;
};

struct C : public A, public B
{
    int z;
};

struct D : public A, virtual public B
{
    int z;
};

struct E : public A, public B
{
    virtual void test(){};
    int z;
};

int main( int argc, char** argv )
{
    printf( "A,C          %d\n", (int)boost::is_virtual_base_of<A,C>::value );
    printf( "B,C          %d\n", (int)boost::is_virtual_base_of<B,C>::value );

    printf( "A,D          %d\n", (int)boost::is_virtual_base_of<A,D>::value );
    printf( "virtual B,D  %d\n", (int)boost::is_virtual_base_of<B,D>::value );

    printf( "A,E          %d\n", (int)boost::is_virtual_base_of<A,E>::value );
    printf( "B,E          %d\n", (int)boost::is_virtual_base_of<B,E>::value );

    printf( "sizeof(A) %ld\n", sizeof(A) );
    printf( "sizeof(B) %ld\n", sizeof(B) );
    printf( "sizeof(C) %ld\n", sizeof(C) );
    printf( "sizeof(D) %ld\n", sizeof(D) );
    printf( "sizeof(E) %ld\n", sizeof(E) );
    return 0;
}

================
A,C          0
B,C          0
A,D          1
virtual B,D  1
A,E          1
B,E          1
sizeof(A) 4
sizeof(B) 4
sizeof(C) 12
sizeof(D) 24
sizeof(E) 24

On Feb 11, 2010, at 12:59 PM, John Maddock wrote:

>> cast the bool to an int, still does not work.    It works for most cases, for example this works:
>> 
>> struct C : public A, public B
>> {
>> virtual test(); //
>> }
>> 
>> struct C : public A, public B
>> {
>> virtual test();
>> float    parameter; // DOESN"T WORK ANY MORE
>> };
>> 
> 
> Which specific compiler version?  I need something that I can reproduce here... John.
> 
> _______________________________________________
> Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost