C++ :: How To Create A Base Class Which Defines Static Data Member

Basically I want to create a base class which defines a static data member so that its automatically redeclared as the same static data member in the derived class.

class A{
protected:
static derivable int val;
// A::val
}

class B : public A{
// static derivable int val is already here
// A::val AND B::val
}

This seems impossible to me but I'm wondering if perhaps there's a way to add modifiers to the compiler to do this (or preferably something MUCH simpler)...