C++实现交易存储链表编译报'head未在作用域声明'错误求助

需求说明 #

1. 编写链表类（含Node节点类和List链表类）存储交易中的商品条目；
2. 测试类功能，打印链表中存储的商品条目；
3. 展示交易的总价格；
4. 从链表中删除一个商品条目后输出新的交易总价格。
   输出格式参考如下：

BC Items Price
10 Pagoda Gnut 110g       3.49     11 Hup Seng Cream Cracker 4.19
12 Yit Poh 2n1 Kopi-o     7.28     13 Zoelife SN & Seed      5.24
14 Gatsby S/FO Wet&Hard   16.99     15 GB W/G U/Hold 150g     6.49
Total (GST Incl.) 43.68

报错原因 #

报错[Error] 'head' was not declared in this scope由两个问题共同导致：

• head是List类的私有成员变量，类外的main函数没有权限直接访问，无法在main中直接取&head
• List类中声明的成员函数print(Node **head)实现时未加List::作用域限定，变成了全局函数，成员函数声明与实现不匹配

修改步骤 #

1. 调整List类的print函数声明，无需额外传参，成员函数可直接访问私有head
2. 修正print函数实现，加上List::作用域，直接使用类内的head变量
3. 调整main函数中的print调用逻辑，不需要传入参数
4. 补充缺失的头文件，调整输出格式匹配参考要求

完整可运行代码 #

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

// Node class
class Node {
public:
    double data;
    string item;
    Node* next;
    Node() {};
    void setData(double aData) {data = aData; };
    void setString(string aItem) {item = aItem;};
    void setNext(Node* aNext) {next = aNext; };
    double Data() {return data; };
    string String() {return item;};
    Node* Next() {return next; };
};

// List class
class List {
    Node *head;
    public:
        List() { head = NULL; };
        void addNode(double data, string item);
        void total();
        void print();
};

//add a node to the list at tail
void List::addNode(double n, string m) {
    Node *newNode = new Node();
    newNode->setData(n);
    newNode->setString(m);
    newNode->setNext(NULL);

    // Create a temp pointer
    Node *tmp = head;
    if ( tmp != NULL ) {
        // Nodes already present in the list
        while ( tmp->Next() != NULL ) {
            tmp = tmp->Next();
        }
        // Point the last node to the new node
        tmp->setNext(newNode);
    } else {
        // First node in the list
        head = newNode;
    }  
} 

void List::print(){
    Node* a = head;
    cout << "========================================" <<endl;
    cout << left << setw(30) << "BC Items" << "Price" <<endl;
    cout << "========================================" <<endl;

    while(a){
        cout << left << setw(30) << a->item << a->data << endl;
        a = a->next;
    }
    cout << "========================================" <<endl;
}

void List::total(){
    Node* cur = head;
    double sum=0;
    cout << left << setw(30) << "Total (GST Incl.)";
    while (cur){
        sum = sum + cur->data;
        cur = cur->next;
    }
    cout << sum << endl;
    cout << "========================================" <<endl;
}

int main() {
    List list;
    list.addNode(3.49, "10 Pagoda Gnut 110g");  
    list.addNode(4.19, "11 Hup Seng Cream Cracker");
    list.addNode(7.28, "12 Yit Poh 2n1 Kopi-O");
    list.addNode(5.24, "13 Zoelife SN & Seed");
    list.addNode(16.99, "14 Gatsby S/FO Wet&Hard");
    list.addNode(6.49, "15 GB W/G U/Hold 150g");

    list.print();  
    list.total();
    return 0;
}

内容的提问来源于stack exchange，提问作者unknown