C++:我的链表尾部没有改变？我似乎无法让节点正确指向彼此？

Question

我正在尝试创建一个包含节点的链表并遍历这些节点。但是，我的链表尾部保持不变，不会更新。

主要内容:

#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
#include "stockclass.h"

using namespace std;

int main()
{

    LinkedList myList;

    ifstream file("stocks.txt");


    string line;
    while (getline(file, line)) 
    {
        stringstream ss(line);
        string symbol;
        string numstr;

        getline(ss, symbol, ',');

        getline(ss, numstr, ',');
        stringstream priceSS(numstr);
        double price = 0;
        priceSS >> price;

        getline(ss, numstr, ',');
        stringstream sharesSS(numstr);
        int numOfShares = 0;
        sharesSS >> numOfShares;

        stock myStock(symbol, price, numOfShares);

        Node newNode(myStock);

        myList.add_node(newNode);

        cout << myList.head << ", " << myList.tail << endl;
        cout << myStock.symbol << ", " << myStock.price << ", " << myStock.numOfStocks << endl;

    };

    MyList.print();
    return 0;

}

stocks.txt 文件

GOOG,250.00,380
APPL,180.00,400
MEIS,46.00,67

.cpp文件

#include <iostream>
#include "stockclass.h"
#include <string>

using namespace std;


stock::stock() {

    symbol = "";
    price = 0.00;
    numOfStocks = 0;
};

stock::stock(string sym, double pri, int num) {

    symbol = sym;
    price = pri;
    numOfStocks = num;


};

stock::printStock() {

    cout << symbol << ", " << price << ", " << numOfStocks;

}




Node::Node(stock myStock) {

    next = NULL;
    s = myStock;

};

void Node::printNode() {

    cout << s.symbol << ", " << s.price << ", " << s.numOfStocks << endl;

};


LinkedList::LinkedList() {

    head = NULL;
    tail = NULL;

};

void LinkedList::add_node(Node& n) {

    if (head == NULL) {
        head = &n;
        tail = &n;

    } else {
        tail->next = &n;
        tail = &n;
        n.next = NULL;
    };

};

void LinkedList::print() {

    head->printNode();
    //Node *tempPointer = tail;

    if (tail != NULL) {

        tail->printNode();
        tail = tail->next;

    };
};

.h文件

using namespace std;
#include <string>
#include <iostream>


class stock {

    public:

        friend ostream& operator<<(ostream &out, stock s);
        string symbol;
        double price;
        int numOfStocks;

        stock();
        stock(string sym, double pri, int num);
        printStock();


};

class Node {

    public:
        Node *next;
        stock s;
        Node();
        Node(stock myStock);
        void printNode();

};

class LinkedList {

    public:

        Node *head;
        Node *tail;

        LinkedList();
        void add_node(Node& n);
        void print();
        static void display(Node *head);

};

这是我尝试使用 linkedlist.print() 时的输出；

https://imgur.com/a/gUo8eFl

linkedlist.print() 输出在 Please insert number choice: 3 之后

不确定我需要修复什么......尾地址在所有 3 个 while 循环中都是相同的。我不知道为什么它没有正确更新。

Answer 1

您应该在 LinkedList 中分配新节点类(class)。为列表分配节点不是调用者的责任。

此外，执行您的 print()方法甚至根本不会尝试遍历列表。

简而言之，你的设计LinkedList类全错了。试试这个:

#include <string>
#include <iostream>

class stock {
public:
    friend std::ostream& operator<<(std::ostream &out, const stock &s);

    string symbol;
    double price;
    int numOfStocks;

    stock();
    stock(string sym, double pri, int num);

    void printStock();
};

class Node {
public:
    Node *next;
    stock s;

    Node(const stock &myStock);

    void printNode();
};

class LinkedList {
public:
    Node *head;
    Node *tail;

    LinkedList();
    ~LinkedList();

    void add_node(const stock &s);
    void print();

    static void display(Node *head);
};

#include <iostream>
#include <string>
#include "stockclass.h"

using namespace std;

stock::stock() {
    symbol = "";
    price = 0.00;
    numOfStocks = 0;
}

stock::stock(string sym, double pri, int num) {
    symbol = sym;
    price = pri;
    numOfStocks = num;
}

void stock::printStock() {
    cout << symbol << ", " << price << ", " << numOfStocks;
}

Node::Node(const stock &myStock) {
    next = NULL;
    s = myStock;
}

void Node::printNode() {
    cout << s.symbol << ", " << s.price << ", " << s.numOfStocks << endl;
}

LinkedList::LinkedList() {
    head = NULL;
    tail = NULL;
}

LinkedList::~LinkedList() {
    Node *n = head;
    while (n) {
        Node *next = n->next;
        delete n;
        n = next;
    }
}

void LinkedList::add_node(const stock &s) {
    Node *n = new Node(s);
    if (!head)
        head = n;
    if (tail)
        tail->next = n;
    tail = n;
}

void LinkedList::print() {
    Node *n = head;
    while (n) {
        n->printNode();
        n = n->next;
    }
}

#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
#include "stockclass.h"

using namespace std;

int main() {
    LinkedList myList;

    ifstream file("stocks.txt");

    string line;
    while (getline(file, line)) {
        istringstream ss(line);
        string symbol;
        string numstr;

        getline(ss, symbol, ',');

        getline(ss, numstr, ',');
        istringstream priceSS(numstr);
        double price = 0;
        priceSS >> price;

        getline(ss, numstr, ',');
        istringstream sharesSS(numstr);
        int numOfShares = 0;
        sharesSS >> numOfShares;

        stock myStock(symbol, price, numOfShares);
        myList.add_node(myStock);

        cout << myList.head << ", " << myList.tail << endl;
        cout << myStock.symbol << ", " << myStock.price << ", " << myStock.numOfStocks << endl;
    }

    MyList.print();
    return 0;
}

到目前为止，这还不是一个完整的实现，但它可以帮助您入门。例如，您需要向 LinkedList 添加一个复制构造函数和一个复制赋值运算符。类，根据 Rule of 3 .并实现你的 operator<<对于 stock .等等。