How to approach implenting a class's methods when these methods depend on another class?

Question

I'm not sure I have all the terminology straight to be able to describe the question, but here's how I'll describe what I'm wondering:

Suppose I have class A, and a second class B that uses data from A in its methods

class A
     {
     data1
     data2
     etc...
     }

class B
     {
     some_data
     method1 
           {
           // do stuff with some_data and A.data1, A.data2
           }
     method2 
           {
           // do other stuff with some_data and A.data1, A.data2
           }
     }

What I'm curious about is, whether as a generality, it is considered better to do something like: 1.

class B
     {
     B(A *a) 
           {
           this->a_ptr = a;
           }
     A *a_ptr

     some_data
     method1()
          { 
          // do stuff with a_ptr->data1, a_ptr->data2
          }
     method2()
           {
           // do other stuff  with a_ptr->data1, a_ptr->data2
           }
     }

versus

2.

class B
     {
     some_data
     method1(A *a)
          { 
          // do stuff with a->data1, a->data2
          }
     method2(A *a)
           {
           // do other stuff  with a->data1, a->data2
           }
     }

Is there a consensus about which approach to use? If so, what are the reasons to prefer one approach over the other?

Answer 1

Rework to inherited as MrLister commented, otherwise Method 1 has object ownership issues. If that's not possible, then use Method 2, but modified as method(A &a) (or method(const A &a) if that's the intention) to clarify the object is required.

Answer 2

From what you have described inheritance seems like the best way to go. Class B would be able to manipulate stuff from Class A and Class B similar to the code below.

From your comment you raise a question about it being an "is-a" relationship. If you don't think there is an "is-a" relationship between A and B then the classes are independent of each other. You shouldn't directly manipulate data from another class. The best solution would be to call member functions from Class A to get the desired results you want in Class B.

class A {
private:
int x,y;
public:
void set_values (int a, int b)
  { x=a; y=b;}
};

class B: public A {
private:
int z;
public:
int GetX ()
  { return x; }
int GetY ()
  { return y; }
int GetZ ()
  { return z; }

};