protected members are not accessible in derived classes

Question

Why is that protected members in the base class where not accessible in the derived class?

class ClassA
{
public:
    int publicmemberA;

protected:
    int protectedmemberA;

private:
    int privatememberA;

    ClassA();
};

class ClassB : public ClassA
{
};

int main ()
{
    ClassB b;
    b.protectedmemberA; // this says it is not accesible, violation?
    //.....
}

Answer 1

You can access protectedmemberA inside b. You're attempting to access it from the outside. It has nothing to do with inheritance.

This happens for the same reason as the following:

class B
{
protected:
   int x;
};

//...

B b;
b.x = 0;  //also illegal

Answer 2

Because the protected members are only visible inside the scope of class B. So you have access to it here for example:

class ClassB : public ClassA
{
    void foo() { std::cout << protectedMember;}
};

but an expression such as

someInstance.someMember;

requires someMember to be public.

Some related SO questions here and here.

Answer 3

You can only access protectedmemberA from within the scope of B (or A) - you're trying to access it from within main()