c++ - Access to method pointer to protected method?

Question

This code:

class B {
 protected:
  void Foo(){}
}

class D : public B {
 public:
  void Baz() {
    Foo();
  }
  void Bar() {
    printf("%x
", &B::Foo);
  }
}

gives this error:

t.cpp: In member function 'void D::Bar()':
Line 3: error: 'void B::Foo()' is protected

• Why can I call a protected method but not take its address?
• Is there a way to mark something fully accessible from derived classes rather than only accessible from derived classes and in relation to said derived class?

---

BTW: This looks related but what I'm looking for a reference to where this is called out in the spec or the like (and hopefully that will lead to how to get things to work the way I was expecting).

Answer 1

You can take the address through D by writing &D::Foo, instead of &B::Foo.

See this compiles fine : http://www.ideone.com/22bM4

But this doesn't compile (your code) : http://www.ideone.com/OpxUy

---

Why can I call a protected method but not take its address?

You cannot take its address by writing &B::Foo because Foo is a protected member, you cannot access it from outside B, not even its address. But writing &D::Foo, you can, because Foo becomes a member of D through inheritance, and you can get its address, no matter whether its private, protected or public.

&B::Foo has same restriction as b.Foo() and pB->Foo() has, in the following code:

void Bar() {
    B b;
    b.Foo();     //error - cannot access protected member!
    B *pB = this;
    pB->Foo();   //error - cannot access protected member!
  }

See error at ideone : http://www.ideone.com/P26JT