Question

Let’s say we have following code:

struct A{
    virtual ~A(){}

    void f(){
        p = 42;
    }

    int p;
};

struct B : public virtual A{};
struct C : public virtual A{};
struct D : public B, public C, public A{}; //let's add non-virtual inheritance

int main(){
    D* pA = new D();
    pA->A::f(); //!

    return 0;
}

Is there any way to set p to 42 in the most base class A?
Following construction pA->A::f(); sets p to 42 for non-virtual inherited class A. Can we do that without cast?

Answer 1

First off, there is no cast: you just qualify which version of A you want as there are more than one. Of course, the notation you have chosen actually doesn’t work because it doesn’t resolve the ambiguity in the first place. I guess you meant to use something like

pA->B::f();

If you don’t want to put the burden of choosing which member function to call on the user of your class, you’ll have to provide suitable forwarding functions for D e.g.:

void D::f() { this->B::f(); }