Question

我在Reddit发布了同样的帖子，但是没有得到任何评论，所以我决定看看我是否可以在这里得到一些帮助。

我当前的项目给出了一个双向链表.h文件和一个.cpp文件，我们需要在.cpp中实现.h。我现在真的在与链接列表挣扎，我觉得即使我有正确或有点正确的事情都是草率的，并没有满足全部要求。这是.h文件：

#include <string>
using namespace std;

struct Node{
    string ssn;
    string name;
    Node* succ;
    Node* pred;
};

class DLL{
    private:
    Node* headPtr;
    int itemCount;

    public:
    DLL();
    DLL(DLL& n);
    virtual ~DLL();
    Node* getHeadPtr();
    int search(string ss)const;
    bool insert(string ss, string name, int & count);
    bool remove(string ss, int & count);
    int size();
    void display();
};

这是.cpp文件：

#include "DLL.h"
#include <iostream>
#include <string>
using namespace std;

// default constructor is already implemented
// do not modify the default constructor
DLL::DLL(){
    headPtr = nullptr;
    itemCount=0;
}

// return the head pointer of the list
// it is already implemented, do not modify it
Node* DLL::getHeadPtr(){
    return headPtr;
}

// copy construct, which copies an existing list n
// the new list is a different object from n
// the new list and object n have the same contents
// Please implement it
DLL::DLL(DLL& n){
        /*Node *first = n.getHeadPtr();
    first = headPtr;
    while(headPtr->succ)
        headPtr = headPtr->succ;
    while(headPtr){
        first->succ = headPtr->succ;
        headPtr->succ = headPtr->succ->succ;
    }*/
}

// destructor
// release every node of the list
// Please implement it
DLL::~DLL(){
    Node *tmp = this->headPtr;
    Node *temp;
    while(tmp->pred)
        tmp = tmp->pred;
    while(tmp)
    {
        temp = tmp->succ;
        delete tmp;
        tmp = temp;
    }
    tmp =NULL; 
    temp = NULL;
}

// if some node has SSN matcthes string ss
// return the index value of the node
// the index value of the first node is 0, the second node is 1, etc.
// if there is node matching ss, return -1
int DLL::search(string ss)const{  
    int count = 0;
    Node *tmp = headPtr;
    while(tmp != NULL){
        count++;
    if(tmp->ssn == ss)
      return count -1;
    tmp = tmp->succ;
  }
    return NULL;
}

// insert (ss, name) to the existing list
// the SSN values are each node are organized in INCREASING order
// if there is a node matching ss value, return false; otherwise true
// else create a node with (ss, name), insert the node to the proper position
// parameter count is the counter of number of valid insertion
// when you implement this method, consider the following situations:
// 1. list is empty
// 2. node should be inserted to the beginning of the list
// 3. node should be inserted to the middle of the list
// 4. node should be inserted to the end of the list
//I use the append function, then sort afterwards
bool DLL::insert(string ss, string name, int & count){
   //Create Node
   Node *newPtr = new Node;
   newPtr->ssn = ss;
   newPtr->succ = NULL;
   //If list is empty
   if(headPtr == NULL){
        headPtr = newPtr;
        return true;
   }
   //If list is not empty
   else{
        Node* temp = headPtr;
        while(temp->succ != NULL){
            temp = temp->succ;
            itemCount++;
            count++;
        }
    temp->succ = newPtr;
    //Following part is to sort from least to greatest (based on Lab 7)
    //Store head to temp node
    temp = headPtr;
    string tempVal;
    int counter = 0;
    //Set temp to next, increase count
    while (temp){
        temp = temp->succ;
        counter++;
    }
    //Make temp head again
    temp = headPtr;
    //While less than count and has next node, check if val at temp is greater than val at next
    for (int j=0; j<count; j++){
        while (temp->succ){
            if (temp->ssn > temp->succ->ssn ){
                //Store val at temp to temp val
                tempVal = temp->ssn ;
                //Make temp's val the value at temp->next
                temp->ssn  = temp->succ->ssn;
                //Make temp->next's val, temp's old val
                temp->succ->ssn  = tempVal;
            }
            //Make temp the next value and check again
            temp = temp->succ;
        }
        //Move temp back to head    
        temp = headPtr;
    }
    return true;
   }
    return false;
}


// remove node containing ss value
// if there is no node containing ss, return false; otherwise true
// consider the following situations:
// 1. list is empty
// 2. node containing ss value is the first node
// 3. node containing ss value is in the middle of the list
// 4. node containing ss value is the last node of the list
bool DLL::remove(string ss, int & count){
    /*Node *temp = headPtr;
    while(temp){
        if(temp->ssn == ss){
            temp->pred->succ = temp->succ;
            temp->succ->pred = temp->pred;
            count++;
            return true;
        }
        temp = temp->succ;

    }
    return false;*/
}

// return the number of the nodes
// it is already implemented, do not modify it
int DLL::size(){
    return itemCount;
}

// iterate through each node
// print out SSN and memory address of each node
// do not modify this method
void DLL::display(){
    Node* temp;
    temp = headPtr;
    while (temp!= nullptr) {
        cout << temp->ssn << "\t" << temp << endl;
        temp = temp->succ;
    }
}

我认为我的搜索功能很好，并且带有不要修改的评论的功能是由教授做出来的，所以它们很好，.h文件很好，因为它也包括在内。我真的很挣扎着复制构造函数和删除函数。我的删除功能的当前内容已被注释掉，因为test.exe每次到达时都会崩溃。然后复制构造函数我只是迷失了，我做了很多研究并阅读了其他帖子，但我无法弄明白。我已经注释掉了，因为程序每次到达该函数时都会崩溃，就像使用remove函数一样。我的插入函数应该按顺序插入所有内容，如果已插入则不插入，我将每个项目附加到列表中，然后将它们按顺序排序，从不检查SSN是否已经存在。它有效，但显然不完全。任何建议都会非常有用，因为你可以说我在双重链表上苦苦挣扎。提前谢谢。

Answer 1

似乎构造函数中的空指针有问题

    /*Node *first = n.getHeadPtr();
first = headPtr;
while(headPtr->succ)

此处headPtr是nullptr，因此headPtr->succ会引发运行时错误。

双链表问题（特别是复制构造函数和删除函数）

1 个答案: