将文件读入具有 class 节点结构的链表 C++

Question

我正在尝试将包含字母 "farming" 的文本文件读取到节点链表中。我创建了一个名为 class 的 NumberList，它具有节点的结构。这是 header.

#ifndef NUMBERLIST
#define NUMBERLIST
#include <iostream>

using namespace std;

class NumberList
{
protected:
//declare a class for the list node
//constructor to initialize nodes of list
struct ListNode
{
    char value;
    ListNode *next;

    // Constructor 
    ListNode(char value1, ListNode *next1 = NULL)
    {
        value = value1;
        next = next1;
    }
};

ListNode *head;  //pointer to head of the list

public:
NumberList() { head = NULL; }  //constructor 
~NumberList();      //destructor
void displayList() const;  //print out list
void reverse();

};
#endif

我运行遇到的问题是尝试将文本文件读入 main() 中的链表。

这是我的主要内容：

#include "Numberlist.h"
#include "ReliableNumberList.h"
#include <iostream>
#include <fstream>


using namespace std;

int main()
{

ListNode *letterList = nullptr;  //create a linked list
char letter;
                    //This is where I read the file into the list
//open the file
ifstream letterFile("linkedText.txt");
if (!letterFile)
{
    cout << "Error in opening the file of letters.";
    exit(1);
}
//read the file into a linked list
while (letterFile >> letter)
{
    //create a node to hold this letter
    letterList = new ListNode(letter, letterList);
    //missing a move to the next node?
}
return 0;
}

此读取文件示例来自我的教科书，但其读取的结构不在单独的 class 中。对于我的一生，我无法弄清楚如何在 NumberList class 中引用 ListNode 结构。 Visual Studio 表示 ListNode 和 letterList 未定义。我知道是因为我没有从 NumberList class 中正确引用它们。

如有任何帮助，我们将不胜感激。

Answer 1

您的问题的快速解决方案可能是：

//------------------------------NumberList.hpp-----------------------------

#ifndef NUMBERLIST_HPP
#define NUMBERLIST_HPP
#include <iostream>

class NumberList{
protected:
    //Protected Members can't be used outside the class
    struct ListNode{
        char value;
        ListNode *next;
        ListNode(char value1, ListNode *next1 = NULL){
            value = value1;
            next = next1;
        }
    };
    ListNode *head, *tail;  //class members
    //head always points at the 1st letter, tail is used for quick adding at the end
public:
    NumberList() { head = NULL; tail = NULL; }
    ~NumberList(); //don't forget to deallocate space properly at the end
    void displayList() const;  //print out list
    void reverse();
    void add(char newchar) {
        //allocate a new node using the ListNode constructor, by default, next1 will be null
        ListNode *newNode = new ListNode(newchar); //equvalent to ListNode(newchar, NULL);
        if (tail == NULL) { //if no elements in the list, both show to newNode
            tail = newNode;
            head = newNode;
        }else{
            tail->next = newNode; //make last node -> next pointer, point to newNode (new last node)
            tail = tail->next; //make current last node be the actual last node
        }
    }
};
#endif

//------------------------------Main.cpp-----------------------------
#include "Numberlist.hpp"
#include <iostream>
#include <fstream>

using namespace std;

int main(){
    ifstream letterFile("linkedText.txt");
    if (!letterFile){
        cout << "Error in opening the file of letters.";
        exit(-1);
    }

    NumberList numberList;

    char letter;
    while (letterFile >> letter) numberList.add(letter);
}

它稍微改变了您的逻辑，因为您不再向列表中添加列表节点，但我怀疑你不想，无论如何。相反，最好添加字符直接到列表，并让列表处理它的节点（有意义，因为节点结构是受保护的）。

当然 class 需要更多改进，但这应该可以解决您最初的问题。

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