数据结构03：双向链表_dlnode *tailptr什么意思-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_70132617/article/details/124546940

本文介绍了如何实现双链表的基本操作，包括创建链表、初始化、打印链表、插入元素（指定位置）、删除指定元素。代码示例详细展示了插入和删除的两种情况，同时提供了测试用例来验证操作的正确性。文章通过图示和实际代码帮助读者理解双链表的工作原理。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

摘要：在我们对单链表有一定认识并且掌握后，双链表其实是非常简单的，就是加了一个指向前一个结点的指针*previous，在我们进行插入删除等基础操作时，对比单链表只需要增加对previous的操作，稍加思考我们就可以比较容易的实现，所以我在看了老师的代码后跟着写了一个，代码里并没有太多注释。如有不懂的地方可以参考我以前单链表的文章，里面有十分详细的中文注释。

一.代码块
1）创建链表

typedef struct doubleLinkedList
{
	char data;
	struct doubleLinkedList *pre;
	struct doubleLinkedList *next;
}DLNode,*DLNodePtr;

2）初始化链表

DLNodePtr doubleLinkedListInit()
{
	DLNodePtr tempHeader = (DLNodePtr)malloc(sizeof(DLNode));
	tempHeader->data = '\0';
	tempHeader->pre = NULL;
	tempHeader->next = NULL;
	
	return tempHeader;
}

3）打印链表

void printList(DLNodePtr paraHeader)
{
	DLNodePtr p = paraHeader->next;
	
	while(p != NULL)
	{
		printf("%c",p->data);;
		
		p = p->next;
	}
	printf("\r\n");
}

4）插入元素（指定位置插入）

void insertElementByPosition(DLNodePtr paraHeader,char paraChar,int paraPosition)
{
	int i;
	DLNodePtr p,q,r;
	q = (DLNodePtr)malloc(sizeof(DLNode));
	p = paraHeader;
	for(i = 0;i < paraPosition;i ++)
	{
		p = p->next;
		if(p == NULL)
		{
			printf("The position %d is beyond the scope of the list.", paraPosition);
			return ;
		}	
	} 
	
	q->data = paraChar;
	if(p->next == NULL)
	{
		q->next = NULL;
		q->pre = p;
		p->next = q; 
	}
	else
	{
		r = p->next;
		r->pre = q;
		q->next = r;
		p->next = q;
		q->pre = p;
	}
	
}

这里我写代码分成了两种情况写，但实际上两种情况只有一句代码的差别，实际上像老师那样写代码量少，也容易看懂，所以我后面的删除就参考了老师的代码

5）删除指定元素

void deleteElement(DLNodePtr paraHeader,char paraChar)
{
	DLNodePtr p, q, r;
	p = paraHeader;
	
	while((p->next != NULL) && (p->next->data != paraChar))
	{
		p = p->next  ;
	}
	if(p->next == NULL)
	{
		printf("The char '%c' does not exist.\r\n", paraChar);
		return ;
	}
	
	q = p->next;
	r = q->next;
	p->next = r;
	if(r != NULL)
	{
	r->pre = p;
	}
	free(q);
	
}

6）删除指定位置的元素

void deleteElementByPosition(DLNodePtr paraHeader,int paraPosition)
{
	int i;
	DLNodePtr p,q,r;
	p = paraHeader;
	for(i = 0;i < paraPosition;i ++)
	{
		p = p->next;
		if(p == NULL)
		{
			printf("The position %d is beyond the scope of the list.", paraPosition);
			return ;
		}	
	}
	q = p->next;
	r = q->next;
	p->next = r;
	if(r != NULL)
	{
	r->pre = p;
	}
	
	free(q);	
}

实际上两种方法大同小异，差别就是如何帮助p跟随到正确的位置，后续的操作两种方法一样.

7）测试代码

void insertDeleteTest()
{
	DLNodePtr tempList = doubleLinkedListInit();
	insertElementByPosition(tempList, 'H', 0);
	insertElementByPosition(tempList, 'e', 1);
	insertElementByPosition(tempList, 'l', 2);
	insertElementByPosition(tempList, 'l', 3);
	insertElementByPosition(tempList, 'o', 4);
	insertElementByPosition(tempList, '!', 5);
	printList(tempList);
	deleteElement(tempList, 'e');
	deleteElement(tempList, 'a');
	deleteElement(tempList, 'o');
	printList(tempList);

	insertElementByPosition(tempList, 'x', 1);
	printList(tempList);
	deleteElementByPosition(tempList, 0); //边界测试 
	printList(tempList);
	deleteElementByPosition(tempList, 1); //正常测试 
	printList(tempList);
	deleteElementByPosition(tempList, 2); //边界测试 
	printList(tempList);

}

二.插入和删除的图示
在这里插入图片描述

三.全部代码

#include <stdio.h>
#include <malloc.h>

typedef struct doubleLinkedList
{
	char data;
	struct doubleLinkedList *pre;
	struct doubleLinkedList *next;
}DLNode,*DLNodePtr;

DLNodePtr doubleLinkedListInit()
{
	DLNodePtr tempHeader = (DLNodePtr)malloc(sizeof(DLNode));
	tempHeader->data = '\0';
	tempHeader->pre = NULL;
	tempHeader->next = NULL;
	
	return tempHeader;
}

void printList(DLNodePtr paraHeader)
{
	DLNodePtr p = paraHeader->next;
	
	while(p != NULL)
	{
		printf("%c",p->data);;
		
		p = p->next;
	}
	printf("\r\n");
}

void insertElementByPosition(DLNodePtr paraHeader,char paraChar,int paraPosition)
{
	int i;
	DLNodePtr p,q,r;
	q = (DLNodePtr)malloc(sizeof(DLNode));
	p = paraHeader;
	for(i = 0;i < paraPosition;i ++)
	{
		p = p->next;
		if(p == NULL)
		{
			printf("The position %d is beyond the scope of the list.", paraPosition);
			return ;
		}	
	} 
	
	q->data = paraChar;
	if(p->next == NULL)
	{
		q->next = NULL;
		q->pre = p;
		p->next = q; 
	}
	else
	{
		r = p->next;
		r->pre = q;
		q->next = r;
		p->next = q;
		q->pre = p;
	}
	
}

void deleteElement(DLNodePtr paraHeader,char paraChar)
{
	DLNodePtr p, q, r;
	p = paraHeader;
	
	while((p->next != NULL) && (p->next->data != paraChar))
	{
		p = p->next  ;
	}
	if(p->next == NULL)
	{
		printf("The char '%c' does not exist.\r\n", paraChar);
		return ;
	}
	
	q = p->next;
	r = q->next;
	p->next = r;
	if(r != NULL)
	{
	r->pre = p;
	}
	
	free(q);
	
}
void deleteElementByPosition(DLNodePtr paraHeader,int paraPosition)
{
	int i;
	DLNodePtr p,q,r;
	p = paraHeader;
	for(i = 0;i < paraPosition;i ++)
	{
		p = p->next;
		if(p == NULL)
		{
			printf("The position %d is beyond the scope of the list.", paraPosition);
			return ;
		}	
	}
	
	q = p->next;
	r = q->next;
	p->next = r;
	if(r != NULL)
	{
	r->pre = p;
	}
	
	free(q);	
}
void insertDeleteTest()
{
	DLNodePtr tempList = doubleLinkedListInit();
	insertElementByPosition(tempList, 'H', 0);
	insertElementByPosition(tempList, 'e', 1);
	insertElementByPosition(tempList, 'l', 2);
	insertElementByPosition(tempList, 'l', 3);
	insertElementByPosition(tempList, 'o', 4);
	insertElementByPosition(tempList, '!', 5);
	printList(tempList);
	deleteElement(tempList, 'e');
	deleteElement(tempList, 'a');
	deleteElement(tempList, 'o');
	printList(tempList);

	insertElementByPosition(tempList, 'x', 1);
	printList(tempList);
	deleteElementByPosition(tempList, 0); //边界测试 
	printList(tempList);
	deleteElementByPosition(tempList, 1); //正常测试 
	printList(tempList);
	deleteElementByPosition(tempList, 2); //边界测试 
	printList(tempList);

}

int main()
{
	insertDeleteTest();
}

四.代码运行结果
在这里插入图片描述