c++ access-specifier understanding - c++

Question

I have encountered the following response in a thread :
Protected members can be accessed from derived classes. Private ones can't.
class Base {
private:
int MyPrivateInt;
protected:
int MyProtectedInt;
public:
int MyPublicInt;
};
class Derived : Base
{
public:
int foo1() { return MyPrivateInt;} // Won't compile!
int foo2() { return MyProtectedInt;} // OK
int foo3() { return MyPublicInt;} // OK
};
class Unrelated
{
private:
Base B;
public:
int foo1() { return B.MyPrivateInt;} // Won't compile!
int foo2() { return B.MyProtectedInt;} // Won't compile
int foo3() { return B.MyPublicInt;} // OK
};
...
1) my question is:
I have read : "A class derivation list names one or more base classes and has the form:
class derived-class: access-specifier base-class
Where access-specifier is one of public, protected, or private, and base-class is the name of a previously defined class. If the access-specifier is not used, then it is private by default. " and "Private Inheritance: When deriving from a private base class, public and protected members of the base class become private members of the derived class.
"
SO...in our example class Derived : Base is equivalent to class Derived : private Base because no access-specifier has been defined, yet the code works as the writer said, so what am i missing?- i thought that Base class for the class Derived access-specifier is private therefore public and protected members of Base should be private for class Derived and can't be accessed... thanks!

Answer 1

Its a similar kind of idea. Rather than applying to which members of the class you can access, it applies to which base classes you can access.
class A
{
public:
void f();
};
class B : public A
{
public:
void g()
{
f(); // OK
A *a = this; // OK
}
};
class B2 : public B
{
public:
void h()
{
f(); //OK
A *a = this; // OK
};
};
B b;
A& ba = b;
class C : protected A
{
public:
void g()
{
f(); // OK, can access protected base
A *a = this; // OK, can access protected base
}
};
class C2 : public C
{
public:
void h()
{
f(); // OK, can access protected base
A *a = this; // OK, can access protected base
};
};
C c;
c.f(); // Not OK, allthough A::f() is public, the inheritance is protected.
A& ca = c; // Not OK, inheritence is protected.
class D : private A
{
public:
void g()
{
f(); // OK because A is a base of D
A *a = this;
}
};
class D2 : public D
{
public:
void h()
{
f(); //Not OK, A is inherited with private in D
A *a = this; //Not OK
};
};
D d;
d.f(); // Not OK, allthough A::f() is public, the inheritance is private.
D& da = d; // Not OK, inheritence is private.