Initialize static constant member variable in nested class

Question

Given codes in language C++

/* file xxx.hpp */

class A
{
};

class B
{
private:
    class C
    {
        static const A a;
    };
};

How can I initialize the static constant member variable A a in nested class C?

Answer 1

Add the following to exactly one .cpp:

const A B::C::a;

Note that the posted code was only a declaration: this is the actual definition and initialisation.