双向链表之C++实现

双向链表只是在单向链表的基础上增加了一条前向链，其中的很多处理方法都是相似的。比如

求链表长、寻找某一节点等。所有相似的部分就不一一实现了。有兴趣可以参考前面的博文。

以下我实现的双向链表(VC6下实现)。错误之处还请指正。

1、代码组织





2、dll.h双链表及节点的说明

#ifndef _DLL_H_
#define _DLL_H_

#define dataType int
#define endOfData 0

class node
{
public:
	dataType data;    //节点数据
	node *next;       //后向指针(离尾节点近)
	node *pre;        //前向指针(离head近)
};

class dll
{
public:
	dll();
	~dll();
	void create();                      //构造双向链表
	void print();                       //打印链表
	bool insert(int pos,dataType num);  //在位置pos插入num节点.插入完成返回true,否则返回false
	void del(dataType num);             //删除链表中所有的num节点

private:
	int getLength();                    //获取链表包含的节点数目
	node *head;                         //链表头指针
};

#endif

3、dll.cpp双链表类函数

#include <iostream>
#include "dll.h"
using namespace std;

dll::dll()
{
	head = NULL;
}

dll::~dll()
{
	node *ptrNode = head;
	node *ptrNodeTmp = NULL;

	while(ptrNode != NULL)
	{
		ptrNodeTmp =ptrNode->next;
		delete ptrNode;
		ptrNode = ptrNodeTmp;
	}
}

void dll::create()
{
	//第一个节点
	node *ptrNode = new node;
	ptrNode->pre = NULL;
	ptrNode->data = endOfData;
	head = ptrNode;

	bool firstNode = true;      //是否是第一个节点
	dataType num = endOfData;

	while(1)
	{
		cout<<"请输入一个节点数据: ";
		cin>>num;

		if(num == endOfData)
		{
			ptrNode->next = NULL;
			break;
		}

		if(firstNode == false)         //以后的节点都需要new node
		{
			node *ptrNodeTmp = new node;
			ptrNodeTmp->data = num;
			ptrNode->next = ptrNodeTmp;
			ptrNodeTmp->pre = ptrNode;
			ptrNode = ptrNodeTmp;
		}

		if(firstNode == true)         //第一个不需要new node
		{
			ptrNode->data = num;
			firstNode = false;
		}
	}

	if(head->data == endOfData)       //链表中并无数据,需要将第一个节点删除
	{
		delete head;
		head = NULL;
	}
}

void dll::print()
{
	node *ptrNode = head;

	while(ptrNode != NULL)
	{
		cout<<ptrNode->data<<" ";
		ptrNode = ptrNode->next;
	}
	cout<<endl;
}

int dll::getLength()
{
	node *ptrNode = head;
	int num = 0;

	while(ptrNode != NULL)
	{
		num++;
		ptrNode = ptrNode->next;
	}

	return num;
}

bool dll::insert(int pos,dataType num)
{
	if(pos < 0 || pos >= getLength())   //插入的pos不正确(0-getLength()-1)
	{
		return false;
	}

	//找到待插入pos的指针和后一个指针
	node *ptrNodeAhead = head;
	node *ptrNodeFellow = NULL;
	int count = 0;
	while(1)
	{
		if(count++ == pos) break;

		ptrNodeFellow = ptrNodeAhead;
		ptrNodeAhead = ptrNodeAhead->next;
	}

	node *ptr = new node;
	ptr->data = num;
	ptr->pre = ptrNodeFellow;
	ptr->next = ptrNodeAhead;
	if(ptrNodeFellow != NULL)      //不是插入头节点
	{
		ptrNodeFellow->next = ptr;
	}
	else                           //插入头节点,head要改变
	{
		head = ptr;
	}
	ptrNodeAhead->pre = ptr;

	return true;
}

void dll::del(dataType num)
{
	node *ptrNodeAhead = head;    //ptrNodeAhead指向待删除的节点
	node *ptrNodeFellow = NULL;   //ptrNodeFellow指向待删除节点的前一节点(离head近的节点)

	while(ptrNodeAhead != NULL)
	{
		while(ptrNodeAhead->data != num && ptrNodeAhead->next != NULL)  //找到num节点或是搜索结束
		{
			ptrNodeFellow = ptrNodeAhead;
			ptrNodeAhead = ptrNodeAhead->next;
		}

		if(ptrNodeAhead->data == num)          //找到num节点
		{
			node *ptrNode = ptrNodeAhead->next;
			
			if(ptrNodeAhead != head)            //不是删除头节点
			{
				ptrNodeFellow->next = ptrNode;
			}
			else                                //删除头结点要注意head指针的赋值
			{
				head = ptrNodeAhead->next;
			}
			if(ptrNodeAhead->next != NULL)       //不是删除尾节点
			{
				ptrNode->pre = ptrNodeFellow;
			}

			delete ptrNodeAhead;                 //释放num节点

			ptrNodeAhead = ptrNode;
		}
		else                                     //搜索结束
		{
			ptrNodeAhead = NULL;
		}
	}
}

4、mian.cpp测试文件

#include <iostream>
#include "dll.h"
using namespace std;

int main()
{
	dll exp;

	//构建链表并打印
	exp.create();
	exp.print();

	//在位置2插入99999并打印
	exp.insert(2,99999);
	exp.print();
	
	//删除位置2的节点并打印
	exp.del(2);
	exp.print();

	return 0;
}