If I want to have common functions in a class and want to defer implementations of some other functions to derived classes, then we need to use

In this case, you would need to use an abstract class. An abstract class in object-oriented programming is a class that contains at least one abstract method. An abstract method is a method that has a declaration but does not have an implementation.

Here are the steps:

1. Declare an abstract class using the keyword 'abstract'.
2. Inside this abstract class, declare common functions that will have implementations.
3. Still, inside the abstract class, declare other functions that you want to defer their implementations to derived classes. These are your abstract methods. Declare them using the keyword 'abstract'.
4. Create derived classes from the abstract class.
5. Inside each derived class, provide implementations for the abstract methods declared in the abstract class.

This way, all derived classes will have the common functions, and each will have its own implementation of the abstract methods.