Accessing a private struct LinkedList in another Class via function;

Question

Good Day! I'm currently trying to create a database that needs me to create two ADT. One of them has a private struct linkedlist created in this example

The problem is I can't seem to access or at least print out the values inside my struct in a function from another class

here is a sample code I derived from my original

#include <iostream>

using namespace std;
class A;
class B;
class A{
    private:
        struct Node{
            int var1;
            struct Node *next;
        };
        Node *head = NULL;
        int var1 = 10;
        friend class B;
    public:     
        void CNode();
        
};

void A::CNode(){
    Node *CPtr, *NewNode;
    NewNode = new Node; 
    NewNode -> var1 = var1;
    NewNode -> next = NULL;
    if(!head){
        head = NewNode;
    }
    else{
        CPtr = head;
        while(CPtr->next){
            CPtr = CPtr->next;
        }
        CPtr->next = NewNode;
    }
    CPtr = head;
    while(CPtr){
        cout << "Class A: " << CPtr -> var1 << endl <<endl;
        cout << CPtr -> next;
        break;
    }
}

class B{
    A c;
    public:
        void Display();
};

void B::Display(){
    //Problem lies here I think
    A::Node *CPtr;
    CPtr = c.head;
    cout << "Class B Integration: " << CPtr -> var1 << endl;
}

int main()
{
    A a;
    B b;
    a.CNode();
    b.Display();
}

The problem lies within Display(). As you can see I'm trying to access my private struct LinkedList in another class and I have no clue or experience whatsoever on how to do it. I would truly be grateful for a solution.

Answer 1

First of all attribute c in class B is private. There is nowhere in the B class to put that value. So I added a constructor that takes a reference to an instance of A.

What you were doing wrong: c were always having a null pointer. Now something about raw references and pointers. Always check against nullptr. Else, you''ll get undefined behaviour such as nothing displaying.

class B
{
    A& c;

public:
    B(A& c_) : c(c_){};
    void Display();
};

void B::Display()
{
    //Problem lies here I think
    A::Node *CPtr;
    CPtr = c.head;
    if (CPtr != nullptr)
    {
        cout << "Class B Integration: " << CPtr->var1 << endl;
    } else {
        cout << "Class B's A attribute is null" << endl; 
    }
}

int main()
{
    A a;
    B b(a);
    a.CNode();
    b.Display();
}