如何在 C++ 中为迭代器 class 创建链表的构造函数？

Question

当我尝试运行此代码时，出现此错误：

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;
}

我不确定如何解决这个问题，感谢任何帮助！

Answer 1

您可以做几件事。您可以将其声明为指针

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

在这种情况下，您需要像这样在 LinkedList 构造函数中调用 point 的构造函数。

Linkedlist::Linkedlist() {
        N = 0;

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

或者，您可以为迭代器创建默认构造函数 class。

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

最后，您可以使用此语法指示程序在为 LinkedList 分配内存之前使用空指针分配点。

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

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

如何在 C++ 中为迭代器 class 创建链表的构造函数？

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

c++

doubly-linked-list