How about a sort class? You provide the sort, and to use it someone declares a SUBCLASS of your sort and has to define the COMPARE and SWAP methods.

sort of like qsort() in the standard library except that instead of passing IN a compare proc it is an overrided virtual method.

Hi,
I am Rammohan from Bangalore and working as a Technical lead in big IT firm .
Solution for your answer is follows:

What do you want to deliver? You have not specified what you need....
Any way based on my understanding you need to know

1) what is class? How we can implement it?
2) What is inheritance and how we can implement it?

If your answer is YES, then read the following my information and it may help you for your studies or your requirmenet may solve by this...

Classes are data types based on which objects are created. Objects with similar properties and methods are grouped together to form a Class. Thus a Class represents a set of individual objects. Characteristics of an object are represented in a class as Properties. The actions that can be performed by objects become functions of the class and are referred to as Methods.
For example consider we have a Class of Cars under which Santro Xing, Alto and WaganR represents individual Objects. In this context each Car Object will have its own, Model, Year of Manufacture, Colour, Top Speed, Engine Power etc., which form Properties of the Car class and the associated actions i.e., object functions like Start, Move, Stop form the Methods of Car Class.
No memory is allocated when a class is created. Memory is allocated only when an object is created, i.e., when an instance of a class is created.
Inheritance:

Inheritance is the process of forming a new class from an existing class or base class. The base class is also known as parent class or super class, The new class that is formed is called derived class. Derived class is also known as a child class or sub class. Inheritance helps in reducing the overall code size of the program, which is an important concept in object-oriented programming.
Inheritance is a means of specifying hierarchical relationships between types C++ classes can inherit both data and function members from other (parent) classes. Terminology: "the child (or derived) class inherits (or is derived from) the parent (or base) class"
When would I use inheritance?
As a specification device.
Human beings abstract things on two dimensions: part-of and kind-of. A Ford Taurus is-a-kind-of-a Car, and a Ford Taurus has-a Engine, Tires, etc. The part-of hierarchy has been a part of software since the ADT style became relevant; inheritance adds "the other" major dimension of decomposition.

____________________
Regards,
Rammohan Alampally,
<snip false signature>

Yes, I don't have any ideas why to discuss a delivering of a program that demonstraits classes and inheritance on C language forum...

There are lots of examples. For instance

class Person
class student : public person
class teacher : public person
class university : public student, teacher

class animal
class dog : public animal
class cat : public animal