C语言超详细介绍与实现线性表中的带头双向循环链表

typedef int DataType;
typedef struct DListnode
{
	DataType data;
	DListNode* prev;
	DListNode* next;
}DListNode;

void DListInint(DListNode** pphead)
{
	*pphead = (DListNode*)malloc(sizeof(DListNode));
	(*pphead)->next = (*pphead);
	(*pphead)->prev = (*pphead);
}

DListNode* DListInit()
	{
		DListNode* phead = (DListNode*)malloc(sizeof(DListNode));
		phead->next = phead;
		phead->prev = phead;
		return phead;
	}

DListNode* BuyDListNode(DataType x)
{
	DListNode* temp = (DListNode*)malloc(sizeof(DListNode));
	if (temp == NULL)
	{
		printf("malloc fail\n");
		exit(-1);
	}
	temp->prev = NULL;
	temp->next = NULL;
	temp->data = x;
	return temp;
}

void DListPushBack(DListNode* phead,DataType x)
{
	DListNode* newnode = BuyDListNode(x);
	DListNode* tail = phead->prev;
	tail->next = newnode;
	newnode->prev = tail;
	newnode->next = phead;
	phead->prev = newnode;
}

void DListNodePrint(DListNode* phead)
{
	DListNode* cur = phead->next;
	while (cur != phead)
	{
		printf("%d->", cur->data);
		cur = cur->next;
	}
	printf("NULL\n");
}

void DListNodePushFront(DListNode* phead, DataType x)
{
	DListNode* next = phead->next;
	DListNode* newnode = BuyDListNode(x);
	next->prev = newnode;
	newnode->next = next;
	newnode->prev = phead;
	phead->next = newnode;
}

void DListNodePopBack(DListNode* phead)
{
	if (phead->next == phead)
	{
		return;
	}
	DListNode* tail = phead->prev;
	DListNode* prev = tail->prev;
	prev->next = phead;
	phead->prev = prev;
	free(tail);
	tail = NULL;
}

void DListNodePopFront(DListNode* phead)
{
	if (phead->next == phead)
	{
		return;
	}
	DListNode* firstnode = phead->next;
	DListNode* secondnode = firstnode->next;
	secondnode->prev = phead;
	phead->next = secondnode;
	free(firstnode);
	firstnode = NULL;
}

DListNode* DListNodeFind(DListNode* phead, DataType x)
{
	DListNode* firstnode = phead->next;
	while (firstnode != phead)
	{
		if (firstnode->data == x)
		{
			return firstnode;
		}
		firstnode = firstnode->next;
	}
	return NULL;
}

void DListNodeInsert(DListNode* pos, DataType x)
{
	DListNode* prev = pos->prev;
	DListNode* newnode = BuyDListNode(x);
	newnode->next = pos;
	newnode->prev = prev;
	prev->next = newnode;
	pos->prev = newnode;
}

void DListNodeErase(DListNode* pos)
{
	DListNode* prev = pos->prev;
	DListNode* next = pos->next;
	prev->next = next;
	next->prev = prev;
	free(pos);
	pos = NULL;
}

struct ListNode* middleNode(struct ListNode* head)
{
    struct ListNode* fast=head;
    struct ListNode* slow=head;
    while(fast&&fast->next)
    {
        fast=fast->next->next;
        slow=slow->next;
    }
    return slow;
}