C++双向链表的建立（无头节点）

#ifndef doublychain_#define doublychain_#include<iostream>#include<algorithm>#include"chainNode.h"using namespace std;template<typename T>class doublychain{public:      doublychain();  ~doublychain();void insert(const int theIndex, const T& theElement);void erase(int theIndex);void output(ostream& out);protected:chainNode<T>*firstNode;chainNode<T>*lastNode;int listSize;};template<typename T>doublychain<T>::doublychain(){firstNode = lastNode = NULL;listSize = 0;}template<typename T>doublychain<T>::~doublychain(){while (firstNode != NULL){chainNode<T>*next = firstNode->next;delete firstNode; firstNode = next;}delete firstNode;}template<typename T>void doublychain<T>::insert(const int theIndex, const T& theElement){if (theIndex == 0){firstNode = new chainNode<T>(theElement, firstNode);lastNode = firstNode;firstNode->pre = NULL;lastNode->next = NULL;}else {chainNode<T>*p = firstNode;chainNode<T>*q;for (int i = 0; i < theIndex -1; ++i)p = p->next;p->next = new chainNode<T>(theElement, p->next);q = p->next;q->pre = p;if (theIndex ==listSize)lastNode = p->next;}++listSize;}template<typename T>void doublychain<T>::erase(int theIndex){chainNode<T>*deleteNode;chainNode<T>*q;if (theIndex = 0){deleteNode=firstNode;q = firstNode->next;firstNode = firstNode->next;q->pre = NULL;}else {chainNode<T>*p = firstNode;for (int i = 0; i < theIndex - 1; i++)p = p->next;deleteNode=p->next;q = p->next->next;p->next = p->next->next;q->pre = p;if (deleteNode == lastNode)lastNode = p;}delete deleteNode;--listSize;}//对双向链表进行测试template<typename T>void doublychain<T>::output(ostream& out){/*for (chainNode<T>*p = firstNode; p != NULL; p=p->next)cout << p->element << " ";*/for (chainNode<T>*p = lastNode; p !=NULL; p = p->pre)cout << p->element << " ";}#endif