How to call member function of different class?

Question

https://code.sololearn.com/cyLklw7Tto3B/?ref=app
I want to call fun() function only from class A and object is created of class A.
Please help

Answer 1

The method fun() is not a static method, you need to call it from an object of class B.
To be able to instantiate B, you need a complete definition of the class. However, for a complete definition, you also need a complete definition of A because of the inheritance.
Therefore, you need to delay the definition of A::call() until B is known, resulting in the following structure:

https://code.sololearn.com/ckdbf3Qdter1/?ref=app