双向链表 只是 比 单链表 多了 一个 指向 前驱的 指针，在插入 和 删除 元素的 时候 得多处理一些。其余 没什么 区别。
而循环链表 的 尾指针 不再 指向 NULL，，而是 指向 头指针，这样 既可以循环遍历，又节省 存储空间 。
每种链表 都有 好处，至于 如何 取舍，得看需求。
欢迎指出代码bug
下面 奉上 双向链表的实现代码：
// DoubleLinkList.cpp : 定义控制台应用程序的入口点。//#include "stdafx.h"#include <stdlib.h>typedef int Elelment;enum E_STATE{E_STATE_ERROR = 0,E_STATE_Ok = 1,};//双链表struct DoubleList{Elelment data;DoubleList * pre;DoubleList * next;};E_STATE listInit(DoubleList & list){list.next = NULL;list.pre = NULL;return E_STATE_Ok;}E_STATE listDestory(DoubleList & list){DoubleList * next = list.next;while (next){DoubleList * freeNode = next;next = next->next; free(freeNode);}list.next = NULL;return E_STATE_Ok;}bool listEmpty(DoubleList list){return list.next == NULL ? true : false;}int listLen(DoubleList list){int len = 0;DoubleList * next = list.next;while (next){next = next->next;len ++;}return len;}E_STATE listGetElement(DoubleList list,int index,DoubleList & listElement){int times = 1;DoubleList * next = list.next;while (next && times < index){next = next->next;times ++;}if (next == NULL || times > index){return E_STATE_ERROR;}listElement = *next;return E_STATE_Ok;}DoubleList * listLocate(DoubleList list,Elelment e){DoubleList * next = list.next;while (next){if (next->data == e){return next;}next = next->next;}return NULL;}DoubleList * listPreElement(DoubleList list,Elelment e){DoubleList * pLocate = listLocate(list,e);return pLocate ? pLocate->pre:NULL;}DoubleList * listNextElement(DoubleList list,Elelment e){DoubleList * pLocate = listLocate(list,e);return pLocate ? pLocate->next : NULL;}E_STATE listInsert(DoubleList & list,int index ,Elelment e){DoubleList * pre = &list;//前驱int times = 0;while (pre && times < index – 1){pre = pre ->next;times ++;}if (pre == NULL || times > index – 1){return E_STATE_ERROR;}DoubleList * newNode = (DoubleList *)malloc(sizeof(DoubleList));newNode->pre = pre;newNode->next = pre->next;newNode->data = e;if (pre->next)//必须后继不为空{//后继节点的前驱pre->next->pre = newNode;}pre->next = newNode;return E_STATE_Ok;}E_STATE listDelete(DoubleList & list,int index){DoubleList * next = list.next;int times = 1;while (times < index && next){next = next->next;times++;}if (times > index || next == NULL){return E_STATE_ERROR;}next->pre->next = next->next;if (next->next){next->next->pre = next->pre;}free(next);return E_STATE_Ok;}void listTraverse(DoubleList list){DoubleList * next = list.next;printf("——————-\n");while (next){printf("%d\n",next->data);next = next->next;}printf("——————-\n");}int _tmain(int argc, _TCHAR* argv[]){DoubleList list;//初始化listInit(list);for (int i = 1; i < 11; i++){listInsert(list,i,i);}listTraverse(list);//插入，删除测试listDelete(list,1);listDelete(list,listLen(list));listInsert(list,listLen(list),111);listInsert(list,listLen(list)+1,222);listTraverse(list);//其他函数测试.printf("表长为：%d\n",listLen(list));DoubleList eList;listGetElement(list,5,eList);printf("第五个节点值为：%d\n",eList.data);printf("前驱值为：%d\n",eList.pre->data);printf("后继值为：%d\n",eList.next->data);//最后释放内存。。。listDestory(list);return 0;}执行结果：
一个人身边的位置只有这么多，
