i want this to be working...

I've lots of classes with similar interface. The following class is a placeholder of other classes:

Code:

---

class Derived : public Base {
        static int x;
public:
        Derived() {x = 10;}

        static int get_x() {return x;}
};

int Derived::x = 0;

---

Note that get_x() is needed to be a static function for all of the classes. Now I need to access a Derived* through a Base*:

Code:

---

int main()
{
        Base *b = new Derived;
        cout << b->get_x() << endl;

        delete b;
        return 0;
}

---

My problem is I'm failing to design such a Base class that will allow the above code in main(). b->get_x() should execute the proper derived class's get_x() it is pointing to. Since get_x() must be a static function, I cannot use a virtual method for my Base class. I tried the following versions:

Code:

---

class Base {
public:
        virtual int get_x() {return -1;}
};

---

which returns -1 always and

Code:

---

class Base {
public:
        virtual int get_x() = 0;
};

---

with error in Visual C++ 2005: error C2259: 'Derived' : cannot instantiate abstract class.
Can you help me to design a Base class to allow the code in main()? Thanks for reading this.

You're getting that error because you didn't define get_x in Derived.

As for your problem, why do you need to have a static virtual function (even though it's evidently not possible)? What is the problem behind it?

Well I didn't know that it is impossible to code static virtual function. I did that for lots of similar classes because I wanted the behaviour out of the classes without having to initialize them. Now I need to change this pattern.

static methods are not associated with objects; they are associated with classes

virtual method calls look up what method to call at runtime based on the real class of an object; hence they are inherently associated with objects

so these things are in completely different domains

It would be interesting to know what situation called for this... Perhaps if you show us we can suggest a better alternative.

Actually, this is what I wanted - making static virtual functions. I changed now all of the static class methods to non static, and write abstract base class for them.