// Illustration of how to prevent overriding of virtual functions in a class A, B, C hierarchy.
// Virtual B::vf is final. Prevents overriding of vf in class C.

#include <iostream>

using namespace std;

class A {
private:
   double a;
public:
  A(double a): a(a){};

  void virtual vf(){
    cout << "Virtual vf from A" << endl;
  }
};

class B : public A {
private:
  double b;
public:
  B(double b): A(b-1), b(b){};

  void  vf() override final {
    cout << "Virtual vf from B" << endl;
  }
};

class C : public B {
private:
  double c;
public:
  C(double b): B(b-1), c(b){};

  void  vf() override{                        // error: overriding final function 'virtual void B::vf()'
    cout << "Virtual vf from C" << endl;
  }
};

void f(){
  A *a1 = new C(5.0);
  
  a1->vf();

  delete a1;
}  

int main(){
  f();
}