Question

我无法对我的双重链表进行深层复制。这是一个家庭作业，所以我想知道为什么我的代码不起作用，而不是得到我不理解的工作代码。

这是我的班级：

#include "textAnalyzer.h"
#include <string>
#include <iostream>
#include <sstream>

TextAnalyzer::Node* TextAnalyzer::createNode(const string& word, const int wordFrequency, 
Node* const previous, Node* const next)
{
return new Node(word, wordFrequency, previous, next);
}
void TextAnalyzer::releaseNodes()
{
Node* del = tail;

while(tail != NULL)
{
    tail = tail->previous;
    tail->next = del;
    delete del;
    del = tail;
}

delete [] head;
delete [] tail;

head = tail = del = NULL;
}

void TextAnalyzer::copyNodes(Node* const copyHead)
{
head = new Node(*copyHead);
Node* iter = head->next;

for(Node* np = copyHead->next; np != NULL; np = np->next)
{
    iter->next = new Node(*np);
    iter = iter->next;
}

iter = NULL;
}

TextAnalyzer::TextAnalyzer():head(createNode("0",0,NULL,NULL)),tail(head)
{}

TextAnalyzer::TextAnalyzer(const TextAnalyzer& copyObject)
{
copyNodes(copyObject.head);
}

TextAnalyzer::~TextAnalyzer()
{
releaseNodes();
}

TextAnalyzer TextAnalyzer::operator=(const TextAnalyzer& assignObject)
{
return TextAnalyzer(assignObject);
}

void TextAnalyzer::insertWord(const string& word)
{
Node* iter = head->next;

while(iter != NULL)
{
    if(iter->word == word)
        iter->wordFrequency++;
    else if(iter->word[0] == word[0] && iter->next != NULL)
    {
        Node* temp = iter->next;
        iter->next = createNode(word, 1, iter, temp);
        iter = iter->next;
        temp->previous = iter;

        temp = NULL;
    }
    else if(iter->word[0] == word[0] && iter->next == NULL)
    {
        iter = createNode(word, 1, tail, NULL);
        tail = iter;
    }
    else
        iter = iter->next;
}

iter = NULL;
}

int TextAnalyzer::wordCount() const
{
Node* iter = head->next;
int count = 0;

while(iter != NULL)
    count++;

return count;
}

int TextAnalyzer::wordCountWithInitialCharacter(const char startsWith)
{
Node* iter = head->next;
int count = 0;

for(int i = 0; i < wordCount(); i++)
{
    if(startsWith == iter->word[0])
        count++;

    iter->previous = iter;
    iter = iter->next;
}

iter = NULL;

return count;
}

string TextAnalyzer::toString() const
{
Node* iter = head->next;
string desc = "List of words: \n";
ostringstream convert;

for(int i = 0; i < wordCount(); i++)
{
    convert << iter->word[0] << " words:\n"
            << iter->word    << "(" 
            << iter->wordFrequency
            << ")\n";
    iter->previous = iter;
    iter = iter->next;
}

iter = NULL;

return desc + convert.str();
}

这是界面：

#ifndef TEXTANALYZER_H
#define TEXTANALYZER_H

#include <iostream>
#include <string>

using namespace std;

class TextAnalyzer {
private:

/*
 * Class: Node
 *
 * This class represents a node in a sorted doubly linked list that stores a
 * list of words and their frequency of occurrence.
 */
class Node {
public:
    string word;
    int wordFrequency;
    Node* previous;
    Node* next;

    Node(const string& word,
         const int wordFrequency,
         Node* const previous,
         Node* const next)
    : word(word),
      wordFrequency(wordFrequency),
      previous(previous),
      next(next)
    {}
}; // end ListNode
/*********************************************************************/

Node* head;
Node* tail;


/*
 * Releases all the memory allocated to the list.
 */
void releaseNodes();

/*
 * Makes a deep copy of the object.
 */
void copyNodes(Node* const copyHead);

/*
 * Returns a populated Node.
 * Throws a bad_alloc exception if memory is not allocated.
 */
Node* createNode(const string& word,
                 const int wordFrequency,
                 Node* const previous,
                 Node* const next);

public:
/* 
 * Initializes head and tail, each to a dymmy node.
 */
TextAnalyzer();

/*
 * Makes a deep copy of the object passed in.
 * Calls copyNodes() to do the actual work.     
 */
TextAnalyzer(const TextAnalyzer& copyObject);

/* 
 * Releases all the memory allocated to the object.
 * Calls the releaseNodes() method to do the actual work.
 */
~TextAnalyzer();

/* 
 * Makes a deep copy of the rhs object.
 */
TextAnalyzer operator =(const TextAnalyzer& assignObject);

/*
 * Inserts the word in a sorted order into the list. 
 *
 * If no Node exists with that initial character, one is added in
 * sorted order. If one does exist (same word), then the word frequency
 * of that word is incremented by one.
 */
void insertWord(const string& word);

/*
 * Returns a count of all the words in the list.
 */
int wordCount() const;

/* 
 * Returns a count of all the words with the initial character.
 */
int wordCountWithInitialCharacter(const char startsWith);

/*
 * Returns a description of the object. The string is formatted as:
 * [A words:]
 *     [<word>(<count>)]
 *     [<word>(<count>)]
 *     ...
 *
 * [B words:]
 *     [<word>(<count>)]
 *     [<word>(<count>)]
 *     ...
 *
 *...
 */
string toString() const;

};

#endif

我需要使用上面给出的界面。我的问题是我的拷贝构造函数中出现错误，说“对象具有不兼容的限定符”或类似的东西。我假设这是因为copyObject是不变的。但是，我不知道如何做到这一点，有人可以告诉我，我在这里失踪了吗？我对C ++比较陌生，我对Java更有经验，这可能就是为什么我感到困惑。

修改

感谢您的回复。我想我正要弄清楚如何成功地做一个深层复制。我已更新我的代码以显示到目前为止我已完成的内容。现在我已经编译了代码，我遇到了一个新的错误。每次运行它时都会出现“未处理的异常0xc0000005”。我用Google搜索并认为这是由于尝试取消引用空指针而导致的错误。调试器显示它在我的releaseNodes()方法中抛出。

void TextAnalyzer::releaseNodes()
{
Node* del = tail;

while(tail != NULL)
{
    tail = tail->previous; //error on this line
    tail->next = del;
    delete del;
    del = tail;
 }

delete [] head;
delete [] tail;

head = tail = del = NULL;
}

上面只是我的releaseNodes()方法，其中的注释显示调试器发出错误的位置。我喜欢看看我的其他代码是否有效，因为我是C ++的新手，很可能我的逻辑在其他地方也有缺陷，不幸的是，在此错误得到解决之前我无法测试任何东西。我仍在追踪我的代码，试图找到可能导致它的原因。如果有人能指出我正确的方向，我们将不胜感激。

Answer 1

我认为这是它所说的行

void TextAnalyzer::copyNodes(Node* const copyHead)
{
    head->next = new Node(*copyHead);   
}

你只是在头部为一个新的Node对象分配下一个指针。基本上你只复制一个节点，节点跟随头部，而不是整个列表。你对使用while循环在releaseNodes中应该做什么有了正确的想法。

你也在拷贝构造函数中错误地调用它。你在定义中给它一个参数，但是你在构造函数中调用了一个参数。

双重链表的深层副本

1 个答案: