Ambiguity and using declarations

Suppose you have a class named C that inherits from a class named A, and x is a member name of A. If you use a using declaration to declare A::x in C, then x is also a member of C; C::x does not hide A::x. Therefore using declarations cannot resolve ambiguities due to inherited members. The following example demonstrates this:

struct A {
   int x;
};

struct B: A { };

struct C: A {
   using A::x;
};

struct D: B, C {
   void f() { x = 0; }
};

int main() {
   D i;
   i.f();
}

The compiler will not allow the assignment x = 0 in function D::f() because it is ambiguous. The compiler can find x in two ways: as B::x or as C::x.