Question

Let’s say that I have two classes A and B.

class A
{
    private:
        int value;
    public:
        A(int v)
        {
            value = v;
        }
};

class B
{
    private:
        A value;
    public:
        B()
        {
            // Here's my problem
        }

}

I guess it’s something basic but I don’t know how to call A’s constructor.

Also the compiler demands a default constructor for class A. But if A has a default constructor than wouldn’t the default constructor be called whenever I declare a variable of type A. Can I still call a constructor after the default constructor has been called? Or can I declare an instance of a class and then call a constructor later?

I think this could be solved using pointers but can that be avoided ?

I know that you can do something like this in C#.

EDIT: I want to do some computations in the constructor and than initialize the classes. I don’t know the values beforehand.

Let’s say I’m reading the value from a file and then I initialize A accordingly.

Answer 1

Or can I declare an instance of a class and then call a constructor later?

Yes, you can do that. Instead of (A value;) declare (A* value;), and then B’s constructor will be B():value(new A(5)){}.

In the B’s destructor you will have to do delete value;

I think this could be solved using pointers but can that be avoided ?

Yes. Use shared_ptr.