class A{
public:
  int GetpA(){ return pA; }
  void SetpA(int a){ pA=a; }
private:
  int pA;
};

class B :public A{
public:
  void OnB(){}
};

class C :virtual public A, virtual public B{
public:
  Sc(){  /*use GetpA() and SetpA()... */ }
};