[C++] Nested Class

A nested class is declared within the scope of another class. The name of a nested class is local to its enclosing class. Unless you use explicit pointers, references, or object names, declarations in a nested class can only use visible constructs, including type names, static members, and enumerators from the enclosing class and global variables.

A nested class is a member and as such has the same access rights as any other member. The members of an enclosing class have no special access to members of a nested class; the usual access rules shall be obeyed.

class E 
{
    int x;
    class B { };

    class I 
    {
        B b; // OK: E::I can access E::B
            int y;
        void f(E* p , int i)
        {
            p->x = i; // OK: E::I can access E::x
        }
    };

    int g(I* p)
    {
        return p->y; // error: I::y is private
    }
};

Ref

1. The inner class idiom
2. http://www.csie.ntu.edu.tw/~b90102/homework/Java/
3. http://blog.csdn.net/jemmy/article/details/1638296

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