Question

The following code generates warning C4250. My question is, what’s the best solution to it?

class A {   virtual void func1(); }  class B : public A { }  class C : public A {   virtual void func1(); }  class D : public B, public C { }  int main() {   D d;   d.func1(); // Causes warning } 

According to what I’ve read it should be possible to do this:

class D : public B, public C {   using B::func1(); } 

But, this doesn’t actually do anything. The way I’ve currently solved it is:

class D : public B, public C {   virtual void func1() { B::func1(); } } 

What’s everyone’s view on this?

Answer 1

I had the same warning for the following code:

class Interface { public:     virtual void A() = 0; };  class Implementation : public virtual Interface { public:     virtual void A() {}; };  class ExtendedInterface : public virtual Interface {     virtual void B() = 0; };  class ExtendedImplementation : public ExtendedInterface , public Implementation { public:     virtual void B() {}; };  

This bug report for Visual C++ 2005 in msdn suggests that this is a known bug that was considered not important enough to fix… They suggest to disable the warning in this case by using a pragma. I think it is safe also in your case, but you should use virtual inheritance as shown in the answer by Gal Goldman.