What is the difference between public, private, and protected inheritance?

Question

What is the difference between public, private, and protected inheritance in C++?

Answer 1

To answer that question, I'd like to describe member's accessors first in my own words. If you already know this, skip to the heading "next:".

There are three accessors that I'm aware of: public, protected and private.

Let:

class Base {
    public:
        int publicMember;
    protected:
        int protectedMember;
    private:
        int privateMember;
};

• Everything that is aware of Base is also aware that Base contains publicMember.
• Only the children (and their children) are aware that Base contains protectedMember.
• No one but Base is aware of privateMember.

By "is aware of", I mean "acknowledge the existence of, and thus be able to access".

next:

The same happens with public, private and protected inheritance. Let's consider a class Base and a class Child that inherits from Base.

• If the inheritance is public, everything that is aware of Base and Child is also aware that Child inherits from Base.
• If the inheritance is protected, only Child, and its children, are aware that they inherit from Base.
• If the inheritance is private, no one other than Child is aware of the inheritance.