看到这周的作业题之后google了一下，然后果断是想多了，一直在考虑这个双向的list到底要怎么实现，啊  总之是想太多了，其实之前还想着头和尾遇到啊什么的你的prev指向我我的next再指向你，然后头和尾的prev、next要不要换方向什么的。。。结果＝ ＝ 想多了。。。很自然的一个list。。双向的而已。。

上学期指针学的太渣了，最近虽然作业一直都在，不过还是把这个写完了才理解的更清楚一点。。。

另外。。简直是血的教训深刻领悟了内存的问题。。。今天被两个大大嘲笑了T。T：“一年之后还是小白。。。。”。论NULL的必要性！！而且搞懂了内存，虚拟内存，硬盘啊什么的，其实我这种零基础的导论课本当初应该好好研究的。。T.T，只要一点击运行，我的编译器就开始卡，往死里卡，我在这期间写完了高数作业 ＝ ＝ 最后系统告诉我qq和xcode都被迫暂停了，重启之后我看我的硬盘的存储空间还有39G，再一运行就23G了。。之后问了下师兄，然后在点运行之后监测我的内存变化，惊呆了！几秒钟就变到2.03G，然后再一看硬盘是32G（重启之后从39G开始变化的），然后我才搞清楚。。。哦。。忘记说原因了。。。少了一行代码。。。没有把头的prev和尾的next设为NULL！

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题干里给的头文件Doulist.h

#ifndef SSCPP2014_DOULIST_A_H

#define SSCPP2014_DOULIST_A_H

#include <string>

struct DouListNode {

int elem;

DouListNode *prev, *next;

DouListNode(int e = 0, DouListNode *p = 0, DouListNode *n = 0) {

elem = e;

prev = p;

next = n;

}

};

class DouList {

private:

DouListNode *m_head, *m_tail;

public:

DouList();

DouList(const DouList &src);

~DouList();

void clear();

bool empty() const;

std::string to_str() const;

int front() const;

int back() const;

void push_front(const int &e);

void push_back(const int &e);

void pop_front();

void pop_back();

void operator=(const DouList &other);

friend std::ostream& operator<<(std::ostream &out,

const DouList &list);

// non-meaning static value

staticint _error_sign;  // for illegal front()/back()

};

#endif

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

题干里给的main函数

#include <iostream>

#include "DouList.h"

usingnamespacestd;

DouList list1, list2;

void display() {

cout << list1.empty() << ':' << list1 << endl;

cout << list2.empty() << ':' << list2.to_str() << endl;

}

int main() {

display();

list1.push_front(894);

list2.push_back(2136);

cout << list1.front() << ',' << list1.back() << endl;

cout << list2.front() << ',' << list2.back() << endl;

display();

list1.push_back(214);

list2.push_front(931);

cout << list1.front() << ',' << list1.back() << endl;

cout << list2.front() << ',' << list2.back() << endl;

display();

for (int i = 0; i < 10; ++i) {

int t;

cin >> t;

list1.push_back(t);

list2.push_front(t);

}

display();

cout<<"###\n";

for (int i = 0; i < 5; ++i) {

list1.pop_front();

list2.pop_back();

}

display();

DouList list3(list1);

list1 = list2;

cout << list1 << endl;

cout << list3 << endl;

return 0;

}

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我忧伤的cpp。。。

#include "DouList.h"

#include <string>

#include<iostream>

usingnamespacestd;

int DouList:: _error_sign = -1;

DouList::DouList() {

m_head = NULL;

m_tail = NULL;

}

DouList::DouList(const DouList &src) {

m_head = NULL;

m_tail = NULL;

DouListNode *temp  = src.m_head;

DouListNode *p = NULL;

if (temp != NULL) {

m_head = new DouListNode(temp->elem, NULL, NULL);

p = m_head;

temp = temp->next;

}

while (temp != NULL) {

p->next = new DouListNode(temp->elem, p, NULL);

temp = temp->next;

p = p->next;

}

m_tail = p;

// *this = src;        ta给的标程一句话就好  T.T

}

DouList::~DouList() {

clear();

}

void DouList::clear() {

while (m_head != NULL) {

DouListNode *a = m_head;

m_head = m_head->next;

delete a;

}

m_head = NULL;

m_tail = NULL;

}

bool DouList::empty() const {

if ((m_tail == m_head) &&(m_head == NULL)){

return true;

} else {

returnfalse;

}

}

string DouList::to_str() const {

string output;

if (this->empty() == true) {

output = "[]";

} else {

output = "[";

DouListNode *p = m_head->next;

long long a = m_head->elem;  // ta说按c＋＋11的标准，此处必须用long long !..

output += to_string(a);

while (p != NULL) {

a = p->elem;

output += ", " + to_string(a);

p = p->next;

}

output += "]";

}

return output;

}

int DouList::front() const {

returnm_head->elem;

}

int DouList::back() const {

returnm_tail->elem;

}

void DouList::push_front(const int &e) {

if (m_head == NULL) {

m_head = new DouListNode(e, NULL, NULL);

m_tail = m_head;

} else {

m_head->prev = newDouListNode( e, NULL, m_head);

m_head = m_head->prev;

}

}

void DouList:: push_back(const int &e) {

if (m_tail == NULL) {

m_tail = new DouListNode(e, NULL, NULL);

m_head = m_tail;

} else {

m_tail->next = newDouListNode( e, m_tail, NULL);

m_tail = m_tail->next;

}

}

void DouList::pop_front() {

if (m_head != NULL) {

DouListNode *a = m_head;

m_head = a->next;

m_head->prev = NULL;  //  ！！！！就是这

delete a;

}

}

void DouList::pop_back() {

if(m_tail != NULL) {

DouListNode *a = m_tail;

m_tail = m_tail->prev;

m_tail ->next = NULL;   // ！！！还有这

delete a;

}

}

voidDouList::operator=(constDouList &other) {

this->clear();

m_head = m_tail = NULL;

if (other.empty())

return;

m_head = newDouListNode(other.m_head->elem);

DouListNode *p = m_head;

DouListNode *q = other.m_head->next;

while (q) {

p->next = new DouListNode(q->elem, p);

p = p->next;

q = q->next;

}

m_tail = p;

}

ostream& operator<<(ostream &out,const DouList &list) {

out << list.to_str();

return out;

}

看硬盘刷刷刷就没了还是蛮好玩的哈哈哈哈。。。＝ ＝ 。。还是挺有收获的。。写谢谢讲代码的室友和“嘲笑”我的大大们和讲解的大大。。。。。