How do I create a class variable that can affect the object passed through the constructor?

Question

So I have class A, which has an object of class B as a class variable. I constructed an object of class B in the main (objB) , and use class A's constructor to pass objB into class A (and assigned it to class variable called objC of type B).

How can I make it so whenever I call objC.do() it can change the original objB as well?

Answer 1

Instead of having a B member, use a reference as a member:

class A {
    B& the_b;
    // etc.
public:
    A(B& some_b) : the_B { some_B } { }
}