This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 116a. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-12-19

747. Access of protected base classes

Consider the following example:

    struct B { void f(){} };
    class N : protected B { };

    struct P: N { friend int main(); };
    int main() {
          N n;
          B& b = n; // R
          b.f();
    }

This code is rendered well-formed by bullet 3 of 11.8.3 [class.access.base] paragraph 4, which says that a base class B of N is accessible at R if

• R occurs in a member or friend of a class P derived from N, and an invented public member of B would be a private or protected member of P

This provision circumvents the additional restrictions on access to protected members found in 11.8.5 [class.protected] — main() could not call B::f() directly because the reference is not via an object of the class through which access is obtained. What is the purpose of this rule?

Rationale (April, 2010):

This is a duplicate of issue 472.