Question

Possible Duplicate:
Are static members inherited? (C++)

If I have a parent class (Base) and it has a static std::map, do Base and Base‘s children all share the same std::map? If not, how can I make them share it?

Answer 1

Yes, they all share it:

class A {
protected:
    static std::map<int,int> x;

public:
    static void push(int a, int b) { x[a] = b; }
};

class B : public A {
public:
    static int size() { return x.size(); }
};

int main() {
    A::push(5,3);
    A::push(4,2);
    std::cout << B::size() << "\n";  // Displays "2"
}

Unless, of course, one of the child classes declares its own member variable with the same name, in which case the base class version will be hidden.