Question

If a class Derived is inherited privately from a class Base and the Derived class has a friend function f(), so what members can f() access from Derived class and Base class.

class Base {
public:
    int a;
protected:
    int b;
private:
    int c;
};  


class Derived: private Base {    
    void friend f() {}

public:
    int d;
protected:
    int e;
private:
    int f;
};

I understand that if a class is inherited privately from the base class, everything is private in the derived class.

But why in the code above, the function f() can access a, b, d, e, f but not c?

Answer 1

‘Friendship’ grants access to the class that declares the friend – it’s not transitive. To use a bad analogy – my friends are not necessarily my dad’s friends.

The C++ FAQ has a bit more detail:

• http://www.parashift.com/c++-faq-lite/friends.html#faq-14.4