C语言建立一个双向循环链表

双向循环链表是一种链表结构，每个节点都包含指向前驱节点和后继节点的指针。它与单向链表不同之处在于，双向循环链表的尾节点指向头节点，头节点的前驱指向尾节点，形成一个环形结构。

以下是一个简单的双向循环链表的代码实现：

#include <stdio.h>
#include <stdlib.h>

// 定义双向循环链表节点结构体
typedef struct node{
    int data;
    struct node *prev;
    struct node *next;
} Node;

// 定义双向循环链表结构体
typedef struct dlist{
    Node *head;
    Node *tail;
} DList;

// 初始化双向循环链表
DList* initDList(){
    DList *list = (DList*) malloc(sizeof(DList));
    list->head = NULL;
    list->tail = NULL;
    return list;
}

// 创建新节点
Node* createNode(int data){
    Node *newNode = (Node*) malloc(sizeof(Node));
    newNode->data = data;
    newNode->prev = NULL;
    newNode->next = NULL;
    return newNode;
}

// 在链表尾部插入新节点
void insertAtTail(DList *list, int data){
    Node *newNode = createNode(data);
    if(list->head == NULL){
        list->head = newNode;
        list->tail = newNode;
        newNode->prev = list->tail;
        newNode->next = list->head;
    } else {
        newNode->prev = list->tail;
        newNode->next = list->head;
        list->tail->next = newNode;
        list->head->prev = newNode;
        list->tail = newNode;
    }
}

// 在链表头部插入新节点
void insertAtHead(DList *list, int data){
    Node *newNode = createNode(data);
    if(list->head == NULL){
        list->head = newNode;
        list->tail = newNode;
        newNode->prev = list->tail;
        newNode->next = list->head;
    } else {
        newNode->prev = list->tail;
        newNode->next = list->head;
        list->head->prev = newNode;
        list->tail->next = newNode;
        list->head = newNode;
    }
}

// 删除指定节点
void deleteNode(DList *list, Node *delNode){
    if(delNode == list->head && delNode == list->tail){
        list->head = NULL;
        list->tail = NULL;
    } else if(delNode == list->head){
        list->head = delNode->next;
        list->tail->next = list->head;
        list->head->prev = list->tail;
    } else if(delNode == list->tail){
        list->tail = delNode->prev;
        list->tail->next = list->head;
        list->head->prev = list->tail;
    } else {
        delNode->prev->next = delNode->next;
        delNode->next->prev = delNode->prev;
    }
    free(delNode);
}

// 打印双向循环链表
void printDList(DList *list){
    if(list->head == NULL){
        printf("Empty List\n");
    } else {
        Node *current = list->head;
        do{
            printf("%d ", current->data);
            current = current->next;
        } while(current != list->head);
        printf("\n");
    }
}

int main(){
    DList *list = initDList();
    insertAtTail(list, 1);
    insertAtTail(list, 2);
    insertAtTail(list, 3);
    insertAtHead(list, 0);
    printDList(list);
    deleteNode(list, list->head->next);
    printDList(list);
    return 0;
}

以上是一个简单的双向循环链表的实现，代码中包含了初始化链表、创建新节点、在链表尾部插入新节点、在链表头部插入新节点、删除指定节点、打印链表等函数。可以根据实际需求进行调整和扩展。