双向链表又称为双链表，使用双向链表的目的是为了解决在链表中访问直接前驱和后继的问题。其设置前驱后继指针的目的，就是为了节省其时间开销，也就是用空间换时间。

在双向链表的每个节点中应有两个链接指针作为它的数据成员：pred指向其前驱节点，next指向其后继节点。再加上数据域，因此每个双向链表至少包括三个域。

 

 

 

 

实现代码如下

//header.h
#include<iostream>
using namespace std;
/*
 * 双向循环链表头文件，
 * 其声明中封装有指向链表附加头节点的头x指针first
 */

template<class T>
struct DbNode
{
	T data;
	DbNode<T> *pred, *next;
	DbNode(T value, DbNode<T> *a = NULL, DbNode<T> *b = NULL):\
		data(value), pred(a), next(b){}
	DbNode(DbNode<T> *a = NULL, DbNode<T> *b = NULL):pred(a), next(b){}
};

template<class T>
class Dblist 
{
private: DbNode<T> *first;
public:
	Dblist(T value);
 	~Dblist(){makeEmpty();}
	void makeEmpty();
	int Length()const;
	bool IsEmpty(){return (this->first->pred == this->pred);}
	DbNode<T> *getHead()const{return this->first;}
	DbNode<T> *Locate(int i, int d);
	DbNode<T> *Search(const T& x);
	bool Insert(int i, const T& x, int d);
	bool Remove(int i, T& x, int d);
	void Print(int d);
};
template<class T>
int Dblist<T>::Length()const
{
	DbNode<T> *tmp = this->first;
	int i = 1;
	while(tmp->next!=this->first)
	{
		++i;
		tmp = tmp->next;
	}
	return i;
}
template<class T>
bool Dblist<T>::Remove(int i, T& x, int d)
{
	DbNode<T> *p = this->Locate(i, d);
	if(!p)
		return false;
	x = p->data;
	if(p==this->first && this->Length()>1)
		this->first = p->next;
	else
		cout<<"仅有头节点的双向循环链表已被删除！请勿在没添加新元素前对其调用。"<<endl;
	p->pred->next = p->next;
	p->next->pred = p->pred;
	delete p;
	return true;
}
template<class T>
DbNode<T>* Dblist<T>::Search(const T& x)
{
	DbNode<T> *tmp = this->first;
	do
	{
		if(tmp->data==x)
		{
			cout<<"address of x is "<<tmp<<"   x = "<<tmp->data<<endl;
			return tmp;
		}
		tmp = tmp->pred;
	}while(tmp!=this->first);
	return NULL;
}
template<class T>//定位元素，d=0时从头节点向前(pred)查第i个元素，d!=0时，从头节点向后(next)找第i个元素
DbNode<T>* Dblist<T>::Locate(int i, int d)
{
	if(this->first->next==this->first || i==0)
		return this->first;
	int t = 1;
	DbNode<T>* tmp = this->first;
	if(d)				//向后找
	{
		while(tmp->next!=this->first && t!=i)//查找到的条件为，在没把双向循环链表遍历一遍前，t=i
		{
			tmp = tmp->next;
			++t;
		}
		if(tmp->next==this->first&&t!=i)
			return NULL;
		else
			return tmp;

	}
	else				//向前找
	{
		while(tmp->pred!=this->first && t!=i)
		{
			tmp = tmp->pred;
			++t;
		}
		if(tmp->pred==this->first&&t!=i)
			return NULL;
		else
			return tmp;
	}
}
template<class T>
bool Dblist<T>::Insert(int i, const T& x, int d)
{
	DbNode<T> *p = this->Locate(i, d);
	if(!p)
		return false;
	DbNode<T> *newnode = new DbNode<T>;
	if(newnode==NULL)
	{
		cout<<"申请内存错误！"<<endl;
		exit(1);
	}
	newnode->data = x;
	if(d)			//p节点后插入
	{
		p->next->pred = newnode;
		newnode->pred = p;
		newnode->next = p->next;
		p->next = newnode;
	}
	else			//p节点前插入
	{
		p->pred->next = newnode;
		newnode->next = p;
		newnode->pred = p->pred;
		p->pred = newnode;
	}
	return true;
}
template<class T>
void Dblist<T>::makeEmpty()
{
	DbNode<T> *p, *q = this->first->pred;
	while(q != this->first)
	{
		p = q;
		q = q->pred;
		delete p;
	}
}
template<class T>
void Dblist<T>::Print(int d)
{
	if(d)			//正序打印
	{
		cout<<"Positive order: ";
		DbNode<T> *tmp = this->first;
		while(tmp->next != this->first)
		{
			cout<<tmp->data<<"->";
			tmp = tmp->next;
		}
		cout<<tmp->data<<"->over."<<endl;

	}
	else			//逆序打印
	{
		DbNode<T> *tmp = this->first;
		cout<<"Reverse sequence: ";
		while(tmp->pred != this->first)
		{
			cout<<tmp->data<<"->";
			tmp = tmp->pred;
		}
		cout<<tmp->data<<"->over."<<endl;
	}
}

template<class T>
Dblist<T>::Dblist(T value)
{
	this->first = new DbNode<T>(value);
	if(this->first == NULL)
	{
		cerr<<"内存分配错误！"<<endl;
		exit(1);
	}
	this->first->next = this->first->pred = this->first; 
}

 

 

//main.cpp
#include"header.h"

int main()
{
	Dblist<int> dl(888);
	dl.Print(0);
	for(int i=1; i<=4; ++i)
	{
		dl.Insert(1, i, 0);
	}
	dl.Print(1);
	int l = 999, k = 0;
	dl.Insert(0, l, 0);
	//int k = 0;
	dl.Print(1);
	dl.Remove(0, k, 0);
	dl.Print(1);
	k = 5;
　　　　 dl.Search(k);
　　　　 dl.Print(0);
	return 0;
}

 完成效果