question about class derivation in c++?

Question

i want to know some things about class derivation in c++ so i have super class x and an inherited class y and i did this

class x{
    public:a;
    private:b;
    protected:c;
}    
class y:public x{
    public:d;
}

in this case how y can access a,b,and c and by how i mean(public,protected,private)

the second case:

class x{
    public:a;
    private:b;
    protected:c;
}    
class y:private x{
    public:d;
}

the same question?

the third case:

class x{
    public:a;
    private:b;
    protected:c;
}    
class y:protected x{
    public:d;
}

again the same question?

sorry i think i wrote too much bye

If you don't have one, I recommend getting one of the beginner books recommended in [The Definitive C++ Book Guide and List](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) — James McNellis, May 29 '10 at 03:23

Stephen · Answer 1 · 2010-05-29T02:43:30.560

In all forms of inheritance:
- y can look up to its base-class (x) and see public and protected.
- Derived classes of y can see its public and protected members.
- Users of y can see its public members.
- Nobody can see anyone else's privates, unless they're friends.
In public inheritance:
- users of y can look up to x and see public.
In protected inheritance:
- both public and protected parts of x become protected in y
- Derived classes of y can see them.
- Users of y cannot see them.
In private inheritance:
- both public and protected parts of x become private in y:
- Derived lasses of y cannot see them.
- Users of y cannot see them.
- Private inheritance is essentially the same as composition (a private data member).

This C++ FAQ has good information on private and protected inheritance.

In the land of C++, friends can see your privates. Never say never. ;-) — Chris Tonkinson, May 29 '10 at 02:42

score 0 · Answer 2 · answered May 29 '10 at 03:20

A derived class can only access public and protected members of the base class. It cannot access the private members of the base class.
private/public/protected inheritance affects how the members inherited from the base class (X) are accessible to the "users" of the derived class (Y); now, the users could be a class derived from this derived class.
private inheritance is akin to declaring the public and protected members of the base class as private in the derived class.
**protected interitance** is akin to declaring the public and protected members of the base class as protected in the derived class.
**public inheritance** makes the public members of the base class public in the derived class; but the protected members of the base class remain protected in the derived class.

score 0 · Answer 3 · answered May 29 '10 at 03:31

Derived classes cannot access private members of the base class unless the derived class is a friend of the base class.
Inheritance permissions:
- Public - all non-private members of the base class retain their permissions (base: public, derived: public; base: protected, derived: protected)
- Protected - all public members of the base class become protected in the derived class; protected members in the base class are still protected (base: public, derived: protected; base: protected, derived: protected)
- Private - all non-private members of the base class become private in the derived class (base: public, derived: private; base: protected, derived: private)

I can't stress enough the fact that private members of a base class are inaccessible by a derived class unless that derived class is declared to be a friend in the base class.

question about class derivation in c++?

3 Answers3