'dependent name is not a type' when using nested nested class in templated class

Question

Does anyone know why the following fails to compile (tested in MSVC2015)?

template<int N> // when this line is removed it compiles successfully
class A {
    class B {
    public:
        class C {
        };
    };
    void func(B b){} // compiles fine
    void func(B::C c){} // generates warning C4346 and error C2061
};

It generates the following on the line marked with a comment:

• warning C4346: 'A<N>::B::C': dependent name is not a type
• error C2061: syntax error: identifier 'C'

Answer 1

Let's google it for you.

The typename keyword is required if a dependent name is to be treated as a type.

C++ rule.

14.6 Name resolution

A name used in a template declaration or definition and that is dependent on a template-parameter is assumed not to name a type unless the applicable name lookup finds a type name or the name is qualified by the keyword typename.