Question

Is the following standard conforming? Can you cite the section?

struct A
{
    virtual void func() = 0;
};

struct B
{
    void func(){}
};

struct C : public A, public B
{
    virtual void func(){ B::func(); }
};

I’m getting a strange compiler warning in VS2010 in equivalent but more complicated code pointing to func‘s declaration in the derived-most class: warning C4505: unreferenced local function has been removed. I have no idea why the compiler thinks a virtual function declared in a class is a local; however I can’t repro that warning in a simpler example.

Edit:

I figured out a small repro case for the warning. I think I was going down the wrong path assuming it was related to function hiding. Here’s the repro case:

template<typename T>
struct C
{
    int GetType() const;
    virtual int func() const;   // {return 4;}  //  Doing this inline removes the warning <--------------
};

template<typename T>
int C<T>::GetType() const
{
    return 0;
}

template<>
int C<int>::GetType() const
{
    return 12;
}

template<typename T> 
int C<T>::func() const
{
    return 3; 
}

//  Adding the following removes the warning <--------------------
//  template<>
//  int C<int>::func() const
//  {
//      return 4;
//  }

I’m fairly sure this is just a VS2010 bug.

Answer 1

The code is well-formed. C::func overrides A::func. B::func is an unrelated function. The spec reads (10.3/2):

If a virtual member function vf is declared in a class Base and in a class Derived, derived directly or indirectly from Base, a member function vf with the same name, parameter-type-list, cv-qualification, and ref-qualifier (or absence of same) as Base::vf is declared, then Derived::vf is also virtual (whether or not it is so declared) and it overrides111 Base::vf.

C::func has the same name as A::func and A::func is virtual, therefore C::func overrides A::func. B::func has no relation to A::func; I don’t know that there is any language in the spec that expressly addresses that scenario.

The Visual C++ 11 Beta compiler does not emit any warnings or errors for this code.