Multiple Inheritance Diamond with Overriding, egcs problem?

[Greg Badros]

I've a question regarding overriding of a method inherited from a class
at the top of the diamond in the famous MI virtual base class example.

Here's the specific code:

#include <iostream.h>

class C {
public:
  C() { }
  virtual void m() { cout << "C::m()" << endl; }
};

class A : public virtual C {
public:
  A() { }
  virtual void m() { cout << "A::m()" << endl; }
  virtual void j() { m(); }
};

class B : public virtual C {
public:
  B() { }
  virtual void m() { cout << "B::m()" << endl; }
};

class D : public B, public A {
public:
  D() { }
};

int main()
{
  D d;  /* egcs-1.02 gives me an error about virtual functions here */
}



This creates:


   C
 /   \
A     B
 \   /
   D

and I expect to get some kind of ambiguity error, since D::m() is
ambiguous. Instead, egcs-1.02 reports:

mult-inheritance-and-overriding3.cc: In function `int main()':
mult-inheritance-and-overriding3.cc:39: cannot declare variable `d' to be of type `D'
mult-inheritance-and-overriding3.cc:39:   since the following virtual functions are abstract:
mult-inheritance-and-overriding3.cc:39:         void B::m()

Could this error message be in need of a rewrite?  The ambiguity results
in a similar need as when inheriting an abstract virtual function
(specifically, to define D::m()), but I think the error message is
confusing, since I do not have any abstract virtual functions defined in 
the above code.

Thanks,
Greg J. Badros
gjb@cs.washington.edu
Seattle, WA  USA
http://www.cs.washington.edu/homes/gjb