双链表列表问题（具体复制构造函数和删除函数）

Question

我发布了这个帖子到Reddit，但没有得到任何评论，所以我决定看看我能否在这里得到一些帮助。

我目前的项目中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。尽管我很担心链接列表，但我觉得即使我有权利或有点权利的事情都是sl and不驯的，并且不能满足所有的要求。这里是.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(); 
}; 

，这里是.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; 
    } 
} 

我想我的搜索功能是好的，有评论说，说不要修改功能是由由教授，所以他们很好，和.h文件是好的，因为它也包括在内。尽管如此，我真的很努力地使用复制构造函数和删除函数。我的删除函数的当前内容被注释掉了，因为每次达到它时test.exe都会崩溃。然后复制构造函数我只是失去了，我做了大量的研究和阅读其他帖子，但我无法弄清楚。我有我的意见，因为每次它到达该功能程序崩溃，就像使用删除功能。我的插入函数应该按顺序插入所有内容，如果插入函数已插入，我会将每个项目追加到列表中，然后将它们按顺序排序，从不检查SSN是否已经在。它有效，但显然不完全。任何建议都将是非常有用的，因为你可以告诉我双向链接列表挣扎了很多。先谢谢你。

Answer 1

似乎在构造

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

这里headPtr与空指针的一个问题是一个nullptr，因此headPtr->succ引发运行时错误。