i want this to be working...

[Donotalo]

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

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*:

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:

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

which returns -1 always and

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.

[Mybowlcut]

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?

[Donotalo]

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.

[spoon!]

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

[Mybowlcut]

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

[Donotalo]

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.