双向循环带头结点链表的常见操作

#include "DList.h"
#include "malloc.h"
#include "assert.h"
#include 
PDLNode BuyDList(DLDataType data)
{
	assert(pHead);
	*pHead = (PDLNode)malloc(sizeof(DLNode));
	if (NULL == *pHead)
	{
		assert(0);
		return;
	}
	*pNewNode->_pNext = NULL;//刚开始给节点并不知道位置所以给NULL
	*pNewNode->_pPre = NULL;
}
}
void DListInit(PDLNode* pHead)//二级指针，为了通过形参去改变实参的值必须得用指针，
                             // 如果本身就是指针则用指针的指针
{
	assert(pHead);
	*pHead = (PDLNode)malloc(sizeof(DLNode));
	if (NULL == *pHead)//此处和下面的*都是解引用，该函数涉及到二级指针，单纯的phead指的是地址
	{
		assert(0);
		return;
	}
	*(pHead)->_pNext = *pHead;
	*(pHead)->_pPre = *pHead;
}
void TestDlist(PDLNode* pHead)//对init测试一下
{
	PDLNode pHead = NULL;
	DListInit(&pHead);//要改变实参得传地址，所以前面都是二级指针
	//“&”可以是取地址符，也可以是引用。此处是引用，形参是是实参的别名，
	//通过引用改变这个值参数的值，相当于改变了主函数里实参的值
		//没有“&”则只是实参的一个拷贝
}
void DListPushBack(DSList* s, SDataType data)//尾插--------有图片E理解
{
	PDLNode pNewNode = BuyDList(data);
	pNewNode->_pPre = pHead->_pPre;
	pNewNode->_pNext = pHead;
	pHead->_pPre->_pNext = pNewNode;
	pHead->_pPre = pNewNode;
}
void DListPopBack(DSList* s)//尾删------------图片E理解
{
	assert(pHead);
	if ((pHead == pHead->_pNext))//没有节点
		return;
	PDLNode pDeLNode = pHead->_pPre;//用PDLNode标记要删除的数据即phead->_pre
	pDelNode->pPre->_pNext = pHead;
	pHead->_pPre = pDelNode->_pPre;
	free(pDelNode)

}
void DlistPushFront(DSList* s, SDataType data)//头插-----图片F理解
{
	PDLNode pNewNode = BuyDList(data);
	pNewNode->_pNext = pHead->_pNext;
	pNewNode->_pPre = pHead;
	pHead->_pNext->_pPre = pNewNode;
	pHead->_pNext = pNewNode;
}
void DlistPopFront(DSList* s)//头删
{
	assert(pHead);
	if ((pHead->_pNext == pHead)//没有节点
		return;
		PDLNode pDeLNode = pHead->_pNext;
		pHead->_pNext = pDelNode->_pNext;
		pDelNode->_pNext->_pPre = pHead;
		free(pDelNode)
}
void DListInsert(PDLNode pos, DLDataType data)//任意位置的插入插在“当前位置的前面”
{
	if (NULL == pos)
		return;
		PDLNode pNewNode = BuyDlist(data);
	pNewNode->pNext = pos;
	pNewNode->_pPre = pos->_pre;
	pos->_pPre = pNewNode;
	pNewNode->_pPre->_pNext = pNewNode;
}
void DListErase(PDLNode data)//任意位置的删除
{
	if (NULL == pos)
		return;
	pos->next->_pPre = pos->_pPre;
	pos->_pPre->_pNext = pos->_pNext;
	free(pos);
}
void DListClear(PDLNode pHead)//清空链表
{
	PDLNode pCur = pHead->_pNext;
	while (pCur != pHead)
	{
		pHead->_pNext = pCur->_pNext;
		free(pCur);
		pCur = pHead->_pNext;
	}
	pHead->_pNext = pHead;
	pHead->_pPre = pHead;
}
void DListDestroy(PDLNode* pHead)//销毁链表，改变指针的指向，所以得用二级指针
{
	DListClear(*pHead);
	free(*pHead);
	*pHead = NULL;
}