How to create a constructor of linked list for iterator class in c++?

Question

When I try to run this code I get this error :

constructor for 'Linkedlist' must explicitly initialize the member 'point' which does not have a default constructor Linkedlist::Linkedlist()

class Node {
    public:
        Node* next;
        Node* prev;
        Elem elem;
        friend class Linkedlist;
        Node(): next(NULL), prev(NULL)
        {}
        Node(Elem elem) : elem(elem)
        {}
};

class Iterator {
private:
    Node* iter;
    //Iterator(Node curr);
public:
    friend class Linkedlist; 
    Iterator(Node* curr) {
        iter=curr;
    } 
};

class Linkedlist { 
private:
    Node *head;
    Node *tail;
    int N;
    Iterator point;
public:
    Iterator point;
    Linkedlist();
};

Linkedlist::Linkedlist() {
    N = 0;
    head = new Node();
    tail  = new Node();
    head->next = tail;
    tail->prev = head;
    point.iter = head;
}

I am not sure how to solve this problem, any help appreciated!

Answer 1

There are a couple of things you could do. You could declare it as a pointer

class Linkedlist { //Missing a c on your class declaration
    private:
        Node *head;
        Node *tail;
        int N;
        //Iterator point; (You have this declared twice)


    public:
        Iterator *point;
        Linkedlist();//s

In this case you'd need to call the constructor for point in the LinkedList constructor like so.

Linkedlist::Linkedlist() {
        N = 0;

        head = new Node();
        tail  = new Node();
        head->next = tail;
        tail->prev = head;
        point = new Iterator(head); // Use the existing constructor
}

Alternatively, you could create a default constructor for the Iterator class.

class Iterator {
           private:
               Node* iter;
           public:
               friend class Linkedlist;
               Iterator() {
                   iter = 0;
               }
               Iterator(Node* curr) {
                    iter=curr;
               } 
        };

Finally, you could use this syntax that instructs the program to allocate point with a null pointer before allocating memory for LinkedList.

Linkedlist::Linkedlist() : point(0) {
        N = 0;

        head = new Node();
        tail  = new Node();
        head->next = tail;
        tail->prev = head;
        point.iter=head;
}