friend class : inherited classes are not friend as well?

Question

In C++, I have a class A which is friend with a class B.

I looks like inherited classes of B are not friend of class A.

I this a limitation of C++ or my mistake ?

Here is an example. When compiling, I get an error on line "return new Memento":

Memento::Memento : impossible to access private member declared in Memento.

class Originator;

class Memento
{
  friend class Originator;

  Memento() {};

  int m_Data;

public:
  ~Memento() {};
};

class Originator
{
public:
  virtual Memento* createMemento() = 0;
};

class FooOriginator : public Originator
{
public:
  Memento* createMemento()
  {
    return new Memento; // Impossible to access private member of Memento
  }
};

void main()
{
  FooOriginator MyOriginator;
  MyOriginator.createMemento();

}

I could of course add FooOriginator as friend of Memento, but then, this means I would have to add all Originator-inherited classes as friend of Memento, which is something I'd like to avoid.

Any idea ?

Answer 1

See: Friend scope in C++
Voted exact duplicate.

I looks like inherited classes of B are not friend of class A.

Correct

I this a limitation of C++ or my mistake ?

It is the way C++ works. I don't see it as a limitation.

Answer 2

Friendship is not inherited, you have to explicitly declare every friend relationship. (See also "friendship isn't inherited, transitive, or reciprocal")