用c++代码写一个链表，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

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

//定义链表节点
typedef struct node {
    int data;
    struct node *next;
}Node, *LinkedList;

//初始化链表
LinkedList InitList() {
    LinkedList L = (LinkedList)malloc(sizeof(Node));
    L->next = NULL;
    return L;
}

//插入节点到链表头部
LinkedList InsertHead(LinkedList L, int data) {
    Node *node = (Node*)malloc(sizeof(Node));
    node->data = data;
    node->next = L->next;
    L->next = node;
    return L;
}

//插入节点到链表尾部
LinkedList InsertTail(LinkedList L, int data) {
    Node *node = (Node*)malloc(sizeof(Node));
    node->data = data;
    node->next = NULL;
    Node *p = L;
    while (p->next != NULL) {
        p = p->next;
    }
    p->next = node;
    return L;
}

//插入节点到某数据之后
LinkedList InsertAfter(LinkedList L, int data, int after) {
    Node *node = (Node*)malloc(sizeof(Node));
    node->data = data;
    Node *p = L->next;
    while (p != NULL && p->data != after) {
        p = p->next;
    }
    if (p == NULL) {
        printf("Insert failed! Cannot find %d in linked list!\n", after);
        return L;
    }
    node->next = p->next;
    p->next = node;
    return L;
}

//插入节点到某数据之前
LinkedList InsertBefore(LinkedList L, int data, int before) {
    Node *node = (Node*)malloc(sizeof(Node));
    node->data = data;
    Node *pre = L;
    Node *p = L->next;
    while (p != NULL && p->data != before) {
        pre = p;
        p = p->next;
    }
    if (p == NULL) {
        printf("Insert failed! Cannot find %d in linked list!\n", before);
        return L;
    }
    node->next = p;
    pre->next = node;
    return L;
}

//修改某个节点的值
LinkedList Modify(LinkedList L, int data, int newData) {
    Node *p = L->next;
    while (p != NULL && p->data != data) {
        p = p->next;
    }
    if (p == NULL) {
        printf("Modify failed! Cannot find %d in linked list!\n", data);
        return L;
    }
    p->data = newData;
    return L;
}

//删除某个节点
LinkedList Delete(LinkedList L, int data) {
    Node *pre = L;
    Node *p = L->next;
    while (p != NULL && p->data != data) {
        pre = p;
        p = p->next;
    }
    if (p == NULL) {
        printf("Delete failed! Cannot find %d in linked list!\n", data);
        return L;
    }
    pre->next = p->next;
    free(p);
    return L;
}

//判断链表是否为空
int IsEmpty(LinkedList L) {
    return L->next == NULL;
}

//判断某个数据是否在链表中
int IsExist(LinkedList L, int data) {
    Node *p = L->next;
    while (p != NULL && p->data != data) {
        p = p->next;
    }
    return p != NULL;
}

//清空链表
LinkedList Clear(LinkedList L) {
    Node *p = L->next;
    while (p != NULL) {
        Node *next = p->next;
        free(p);
        p = next;
    }
    L->next = NULL;
    return L;
}

//排序链表
LinkedList Sort(LinkedList L) {
    Node *p = L->next;
    int temp;
    while (p != NULL) {
        Node *q = p->next;
        while (q != NULL) {
            if (p->data > q->data) {
                temp = p->data;
                p->data = q->data;
                q->data = temp;
            }
            q = q->next;
        }
        p = p->next;
    }
    return L