用C++语言实现一个双向循环链表并生成注释

以下是用 C++ 实现双向循环链表的代码，已加入注释以加深理解：

#include <iostream>
using namespace std;

// 双向循环链表的结点类
class Node {
public:
    int data;   // 数据域
    Node* prev; // 指向前一个结点的指针
    Node* next; // 指向后一个结点的指针
    Node(int d = 0, Node* p = nullptr, Node* n = nullptr) 
        : data(d), prev(p), next(n) {}
};

// 双向循环链表类
class DoubleLinkedList {
private:
    Node* head; // 头结点指针
    Node* tail; // 尾结点指针

public:
    // 构造函数，初始化头结点和尾结点
    DoubleLinkedList() {
        head = new Node();
        tail = new Node();
        head->next = tail;
        tail->prev = head;
    }

    // 在链表尾部插入结点
    void append(int d) {
        Node* newNode = new Node(d, tail->prev, tail);
        tail->prev->next = newNode;
        tail->prev = newNode;
    }

    // 在链表中指定位置插入结点
    void insert(int pos, int d) {
        if (pos < 0 || pos > size()) {
            cout << "Invalid position!" << endl;
            return;
        }

        Node* cur = head->next;
        for (int i = 0; i < pos; i++) {
            cur = cur->next;
        }

        Node* newNode = new Node(d, cur->prev, cur);
        cur->prev->next = newNode;
        cur->prev = newNode;
    }

    // 在链表中删除指定位置的结点
    void remove(int pos) {
        if (pos < 0 || pos >= size()) {
            cout << "Invalid position!" << endl;
            return;
        }

        Node* cur = head->next;
        for (int i = 0; i < pos; i++) {
            cur = cur->next;
        }

        cur->prev->next = cur->next;
        cur->next->prev = cur->prev;
        delete cur;
    }

    // 获取指定位置的结点的数据
    int get(int pos) {
        if (pos < 0 || pos >= size()) {
            cout << "Invalid position!" << endl;
            return -1;
        }

        Node* cur = head->next;
        for (int i = 0; i < pos; i++) {
            cur = cur->next;
        }

        return cur->data;
    }

    // 获取链表的长度
    int size() {
        int count = 0;
        Node* cur = head->next;
        while (cur != tail) {
            count++;
            cur = cur->next;
        }
        return count;
    }

    // 打印链表中所有结点的数据
    void print() {
        Node* cur = head->next;
        while (cur != tail) {
            cout << cur->data << " ";
            cur = cur->next;
        }
        cout << endl;
    }
};

int main() {
    DoubleLinkedList list;
    list.append(1);
    list.append(2);
    list.append(3);
    list.insert(1, 4);
    list.print();   // 输出：1 4 2 3 
    list.remove(2);
    list.print();   // 输出：1 4 3 
    cout << "The size of the list is " << list.size() << endl; // 输出：The size of the list is 3
    cout << "The data of the first node is " << list.get(0) << endl; // 输出：The data of the first node is 1
    return 0;
}