Basic Operation First Node way circular

#ifndef _LIST_H_
#define _LIST_H_

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

typedef int LTDataType;
typedef struct ListNode
{
	LTDataType _data;
	struct ListNode* _next;
	struct ListNode* _prev;
}ListNode;
typedef struct List
{
	ListNode* _head;
}List;

void ListInit(List* plist);
void ListDestory(List* plist);

void ListPushBack(List* plist, LTDataType x);
void ListPopBack(List* plist);
void ListPushFront(List* plist, LTDataType x);
void ListPopFront(List* plist);

ListNode* ListFind(List* plist, LTDataType x);

// 在pos的前面进行插入
void ListInsert(ListNode* pos, LTDataType x);

// 删除pos位置的节点
void ListErase(ListNode* pos);

void ListRemove(List* plist, LTDataType x);
void ListPrint(List* plist);

#endif

#include "List.h"

void ListInit(List* plist)//初始化
{
	plist->_head = (ListNode*)malloc(sizeof(ListNode));
	memset(&plist->_head->_data, 0, sizeof(LTDataType));//清零
	plist->_head->_next = plist->_head->_prev = plist->_head;
}

void ListPushBack(List* plist, LTDataType x)//后插
{
	ListNode * cur = (ListNode*)malloc(sizeof(ListNode));
	cur->_data = x;

	plist->_head->_prev->_next = cur;
	cur->_prev = plist->_head->_prev;
	plist->_head->_prev = cur;
	cur->_next = plist->_head;
}
void ListPopBack(List* plist)//后删
{
	ListNode * tmp = plist->_head->_prev;//找到head的前一个

	if (tmp != plist->_head)//把tmp删除
	{
		tmp->_prev->_next = tmp->_next;
		tmp->_next->_prev = tmp->_prev;
		free(tmp);
	}
}
void ListPushFront(List* plist, LTDataType x)//头插
{
	ListNode * cur = (ListNode*)malloc(sizeof(ListNode));
	cur->_data = x;

	plist->_head->_next->_prev = cur;
	cur->_next = plist->_head->_next;
	plist->_head->_next = cur;
	cur->_prev = plist->_head;
}
void ListPopFront(List* plist)//头删
{
	ListNode * tmp = plist->_head->_next;//找到head的后一个

	if (tmp != plist->_head)//删除tmp
	{
		tmp->_prev->_next = tmp->_next;
		tmp->_next->_prev = tmp->_prev;
		free(tmp);
	}
}

void ListDestory(List* plist)//清除链表
{
	ListNode * tmp = plist->_head->_next;//找到head的后一个

	while (tmp != plist->_head)//删除tmp
	{
		tmp->_prev->_next = tmp->_next;
		tmp->_next->_prev = tmp->_prev;
		free(tmp);
		tmp = plist->_head->_next;
	}
	free(plist->_head);
	plist->_head = NULL;
}
void ListPrint(List* plist)
{
	ListNode * cur = (ListNode*)malloc(sizeof(ListNode));
	for (cur = plist->_head->_next; cur != plist->_head; cur = cur->_next)
	{
		printf("%d<-->", cur->_data);
	}
	putchar('\n');
}

#include "List.h"

int main()
{
	List list;
	ListInit(&list);
	ListPushBack(&list, 7);
	ListPushBack(&list, 6);
	ListPushBack(&list, 5);
	ListPushBack(&list, 4);
	ListPushBack(&list, 3);
	ListPushBack(&list, 2);
	ListPrint(&list);
	system("pause");
	return 0;
}