How to Create Function Parameters in abstract classes

An abstract class cannot be used as a function parameter object, but the pointer and reference method of the abstract class can be used. For example, the following function is valid.
Void fun (cabstract * P );
Void fun (cabstract & );
Invalid example: void fun (cabstract OBJ );
The pointer and reference method are valid because the pointer and reference method can point to an object of the derived type of an abstract class. These derived classes may not be abstract classes.

When the parameters are combined, the pointer and reference of the base class are used to point to the object of the derived class.
All methods of the base class can be called normally.

How to Create Function Parameters in abstract classes