How to Call Function of one class on the object of another class?

Question

How can I call one method in one class over using another class ?

I have ;

class A { 
 public :
  foo ( ) ;
};

class B {
 public :
  bar ( ) ;
};

in main :

A data ;          // I am creating instance of class A 

data . bar ( ) ;  //  but, I am calling a method of another class

                  // how can I do that ?

Note : I could not find a appropriate title. If you have one, feel free to share or edit

Solution 1

Unless the two classes are related(through inheritance) You cannot do that.

A member functions performs some action on the instance of the class to which it belongs.
You created an object of class A so you can only call member functions of A through it.

Grinding an Apple and hoping to get a mango shake, won't really happen right.

Solution 2

Use public inheritance:

class B {
 public:
  void bar();
};

class A : public B
{ };

int main() {
 A a;
 a.bar();
}