用c++写一个代码实现常见的链表操作，插入头部，尾部，某数据之后或之前，修改，删除，排序，存储到文件，从文件构建链表，判空，是否存在，清空，排序，

以下是用C语言实现常见的链表操作的代码：

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

// 定义链表节点结构体
typedef struct Node {
    int data;
    struct Node *next;
} Node;

// 定义链表结构体
typedef struct List {
    Node *head;
    Node *tail;
} List;

// 初始化链表
List *initList() {
    List *list = (List *)malloc(sizeof(List));
    Node *head = (Node *)malloc(sizeof(Node));
    head->next = NULL;
    list->head = head;
    list->tail = head;
    return list;
}

// 判断链表是否为空
int isEmpty(List *list) {
    return list->head->next == NULL;
}

// 在链表头部插入节点
void insertHead(List *list, int data) {
    Node *node = (Node *)malloc(sizeof(Node));
    node->data = data;
    node->next = list->head->next;
    list->head->next = node;
    if (list->tail == list->head) {
        list->tail = node;
    }
}

// 在链表尾部插入节点
void insertTail(List *list, int data) {
    Node *node = (Node *)malloc(sizeof(Node));
    node->data = data;
    node->next = NULL;
    list->tail->next = node;
    list->tail = node;
}

// 在某个节点之后插入节点
void insertAfter(List *list, int afterData, int data) {
    Node *node = (Node *)malloc(sizeof(Node));
    node->data = data;
    Node *p = list->head->next;
    while (p != NULL) {
        if (p->data == afterData) {
            node->next = p->next;
            p->next = node;
            if (list->tail == p) {
                list->tail = node;
            }
            break;
        }
        p = p->next;
    }
}

// 在某个节点之前插入节点
void insertBefore(List *list, int beforeData, int data) {
    Node *node = (Node *)malloc(sizeof(Node));
    node->data = data;
    Node *p = list->head;
    while (p->next != NULL) {
        if (p->next->data == beforeData) {
            node->next = p->next;
            p->next = node;
            if (list->tail == p) {
                list->tail = node;
            }
            break;
        }
        p = p->next;
    }
}

// 修改某个节点的值
void modify(List *list, int oldData, int newData) {
    Node *p = list->head->next;
    while (p != NULL) {
        if (p->data == oldData) {
            p->data = newData;
            break;
        }
        p = p->next;
    }
}

// 删除某个节点
void delete(List *list, int data) {
    Node *p = list->head;
    while (p->next != NULL) {
        if (p->next->data == data) {
            Node *temp = p->next;
            p->next = temp->next;
            free(temp);
            if (list->tail == temp) {
                list->tail = p;
            }
            break;
        }
        p = p->next;
    }
}

// 排序链表（升序）
void sort(List *list) {
    Node *p = list->head->next;
    int len = 0;
    while (p != NULL) {
        len++;
        p = p->next;
    }
    for (int i = 0; i < len - 1; i++) {
        p = list->head->next;
        for (int j = 0; j < len - 1 - i; j++) {
            if (p->data > p->next->data) {
                int temp = p->data;
                p->data = p->next->data;
                p->next->data = temp;
            }
            p = p->next;
        }
    }
}

// 存储链表到文件
void save(List *list, char *filename) {
    FILE *fp = fopen(filename, "w");
    Node *p = list->head->next;
    while (p != NULL) {
        fprintf(fp, "%d\n", p->data);
        p = p->next;
    }
    fclose(fp);
}

// 从文件构建链表
List *load(char *filename) {
    List *list = initList();
    FILE *fp = fopen(filename, "r");
    if (fp == NULL) {
        return list;
    }
    int data;
    while (fscanf(fp, "%d", &data) != EOF) {
        insertTail(list, data);
    }
    fclose(fp);
    return list;
}

// 判断某个节点是否存在
int exists(List *list, int data) {
    Node *p = list->head->next;
    while (p != NULL) {
        if (p->data == data) {
            return 1;
        }
        p = p->next;
    }
    return 0;
}

// 清空链表
void clear(List *list) {
    Node *p = list->head->next;
    while (p != NULL) {
        Node *temp = p;
        p = p->next;
        free(temp);
    }
    list->head->next = NULL;
    list->tail = list->head;
}

// 输出链表中的所有元素
void print(List *list) {
    Node *p = list->head->next;
    while (p != NULL) {
        printf("%d ", p->data);
        p = p->next;
    }
    printf("\n");
}

int main() {
    List *list = initList();
    insertHead(list, 3);
    insertHead(list, 2);
    insertHead(list, 1);
    insertTail(list, 4);
    insertAfter(list, 2, 5);
    insertBefore(list, 4, 6);
    modify(list, 2, 7);
    delete(list, 3);
    sort(list);
    save(list, "list.txt");
    List *newList = load("list.txt");
    printf("List: ");
    print(list);
    printf("New List: ");
    print(newList);
    printf("Exists 2: %d\n", exists(list, 2));
    printf("Exists 8: %d\n", exists(list, 8));
    clear(list);
    printf("List is empty: %d\n", isEmpty(list));
    return 0;
}