//  A2_7.cpp

#include <iostream>
using namespace std;

class A { protected: int x; public: A() { cout << "\n  constructing A"; } };
class B { protected: int x; public: B() { cout << "\n  constructing B"; } };

//  C class fails to compile since mf() is ambiguous - which x?
/*
class C1 : public A, public B { public:  void mf() { x; }  };
*/
// method #1 - removing ambiguity
class C2 : public A, public B { 
  public:  
    C2() { cout << "\n  constructing C2"; }
    void mf() { ++A::x; }  
};
/*
   method #2 - this doen't work
class AD : public virtual A { };
class BD : public virtual B { };
class C5 : public AD, public BD { public:  void mf() { ++x; }  };
*/
// method #3 - but this is ok
class base { 
  protected: int x; 
  public:
    base() { cout << "\n  constructing base"; } 
};
class AB : public virtual base { 
  public: 
    AB() { cout << "\n  constructing AB"; } 
};
class BB : public virtual base {
  public: 
    BB() { cout << "\n  constructing BB"; } 
};
class C6 : public AB, public BB { 
  public: 
    C6() { cout << "\n  constructing C6"; }
    void mf() { ++x; } 
};

void main() {

  C2 c2;
  c2.mf();
  
  C6 c6;
  c6.mf();
  cout << "\n\n";
}