用于类和结构之间交互的 C++ 语法答案

【问题标题】：C++ syntax for interaction between classes and struct用于类和结构之间交互的 C++ 语法
【发布时间】：2016-02-24 07:57:04
【问题描述】：

我在 C++ 的第一学期正在做一个作业，但我无法弄清楚它的工作语法。我需要使用指针将结构作为参数传递给类函数。我复制的这段代码是我最好的尝试，它会编译，但当它要求输入名字时它会崩溃。当我尝试更改语法时，我收到有关不完整结构、未定义变量（warrior was 或无效运算符）的错误。我做错了什么？

#include <iostream>

using namespace std;

class StarWars
{
    public:
        int totalNumber;
        struct data_clone
        {
            int ID, timeCounter;
            string name;
        };
        data_clone *warrior;
        void createClone()
        {
            cout << "How many clone warriors do you want to create in total?" << endl;
            cin >> totalNumber;
        }
        void input(struct data_clone *pointer, int total)
        {

            for(int i = 1; i <= total; i++)
            {
                cout << "For warrior number " << i << ":" << endl;
                cout << "What is the warrior's name?" << endl;
                cin >> pointer[i].name;
                cout << "What is the warrior's ID number?" << endl;
                cin >> pointer[i].ID;
                cout << "What is the warrior's time counter?" << endl;
                cin >> pointer[i].timeCounter;
            }
        }
        void lifeSpan(struct data_clone *pointer, int total)
        {
            for(int i = 1; i <= total; i++)
            {
                cout << "Warrior number " << pointer[i].name << ": " << endl;
                while(pointer[i].timeCounter > 0)
                {
                    cout << "Warrior name: " << pointer[i].name << endl;
                    cout << "Warrior ID number: " << pointer[i].ID << endl;
                    cout << "Warrior time counter: " << pointer[i].timeCounter << endl;
                    cout << "Clone is alive." << endl;
                    pointer[i].timeCounter--;
                }
                cout << "Warrior name: " << pointer[i].name << endl;
                cout << "Warrior ID number: " << pointer[i].ID << endl;
                cout << "Warrior time counter: " << pointer[i].timeCounter << endl;
                cout << "Clone is dead." << endl;
            }
        }


};

int main(void)
{
    StarWars clones;
    clones.createClone();
    clones.input(clones.warrior, clones.totalNumber);
    clones.lifeSpan(clones.warrior, clones.totalNumber);
}

【问题讨论】：

似乎warrior 是一个悬空指针。
struct 和 class 在 C++ 中基本相同，因此没有特殊规则可以让一个与另一个“交互”。
你有一个指针，但你从未将它设置为指向任何地方。

标签： c++ pointers struct

【解决方案1】：

您没有初始化内存战士指向的内存，因此您正在使用未初始化的内存 - 总是一件坏事。这里有两点要记住：

使用指针时，总是先初始化它们后面的内存。更喜欢使用 RAII 概念，例如 std::unique_ptr / std::shared_ptr

void DoStuff(Widget* w);

std::unique_ptr<Widget> pw = std::make_unique<Widget>();
DoStuff(w.get());

使用普通变量时，使用解引用/引用运算符获取指向变量的指针。

void DoStuff(Widget* w);

Widget widget;
DoStuff(&w);

【讨论】：

感谢您提供的信息——我现在正在阅读这些智能指针。我不认为教授打算让我们将它们用于这项特定的任务，但我总是很高兴学习更好的做事方法！

【解决方案2】：

struct data_clone
{
    int ID, timeCounter;
    string name;
};

class StarWars
{
private:
       data_clone *warrior;
       int totalNumber;
    public:
        StarWars()
        {

        }
        ~StarWars()
        {
            delete[] warrior; // clean up 
        }

        void createClone();
        void input();
        void lifeSpan();
  };

void StarWars::createClone()
{
    cout << "How many clone warriors do you want to create in total?" << endl;
    cin >> totalNumber;
    // construct structure baased on input
    warrior = new data_clone[totalNumber];
}

 void StarWars::input()
{

    for(int i = 0; i < totalNumber; i++)
    {
        cout << "For warrior number " << i+1 << ":" << endl;
        cout << "What is the warrior's name?" << endl;
        cin >> warrior[i].name;
        cout << "What is the warrior's ID number?" << endl;
        cin >> warrior[i].ID;
        cout << "What is the warrior's time counter?" << endl;
        cin >> warrior[i].timeCounter;
    }
}

void StarWars::lifeSpan()
{
    std::cout<<"**********Print data**********\n";
    for(int i = 0; i < totalNumber; i++)
    {
        cout << "Warrior number " << warrior[i].name << ": " << endl;
        while(warrior[i].timeCounter > 0)
        {
            cout << "Warrior name: " << warrior[i].name << endl;
            cout << "Warrior ID number: " << warrior[i].ID << endl;
            cout << "Warrior time counter: " << warrior[i].timeCounter << endl;
            cout << "Clone is alive." << endl;
            warrior[i].timeCounter--;
        }
        cout << "Warrior name: " << warrior[i].name << endl;
        cout << "Warrior ID number: " << warrior[i].ID << endl;
        cout << "Warrior time counter: " << warrior[i].timeCounter << endl;
        cout << "Clone is dead." << endl;
    }
}

int _tmain(int argc, _TCHAR* argv[])
{
    StarWars clones;
    clones.createClone();
    clones.input();
    clones.lifeSpan();

    return 0;
}

【讨论】：

【解决方案3】：

你从来没有创建过你的克隆，你只知道应该有多少。
为他们分配空间：

void createClone()
{
    cout << "How many clone warriors do you want to create in total?" << endl;
    cin >> totalNumber;
    warrior = new data_clone[totalNumber];
}

您的数组索引也关闭了 - 大小为 N 的数组的索引从 0 到 N - 1。

但更常见的处理方式是将数量传递给构造函数，让对象处理自己的成员：

class StarWars
{
public:
    StarWars(int clones)
        : totalNumber(clones),
          warrior(new data_clone[clones])
    {

    }

    void input()
    {
        for(int i = 0; i < totalNumber; i++)
        {
            cout << "For warrior number " << i << ":" << endl;
            cout << "What is the warrior's name?" << endl;
            cin >> warrior[i].name;
            cout << "What is the warrior's ID number?" << endl;
            cin >> warrior[i].ID;
            cout << "What is the warrior's time counter?" << endl;
            cin >> warrior[i].timeCounter;
        }
    }

    void lifeSpan()
    {
        for(int i = 0; i < totalNumber; i++)
        {
            cout << "Warrior number " << i << ": " << endl;
            while(warrior[i].timeCounter > 0)
            {
                cout << "Warrior name: " << warrior[i].name << endl;
                cout << "Warrior ID number: " << warrior[i].ID << endl;
                cout << "Warrior time counter: " << warrior[i].timeCounter << endl;
                cout << "Clone is alive." << endl;
                warrior[i].timeCounter--;
            }
            cout << "Warrior name: " << warrior[i].name << endl;
            cout << "Warrior ID number: " << warrior[i].ID << endl;
            cout << "Warrior time counter: " << warrior[i].timeCounter << endl;
            cout << "Clone is dead." << endl;
        }
    }

private:
    int totalNumber;
    struct data_clone
    {
        int ID, timeCounter;
        string name;
    };
    data_clone *warrior;
};

int main()
{
    int number = 0;
    cout << "How many clone warriors do you want to create in total?" << endl;
    cin >> number;
    StarWars clones(number);
    clones.input();
    clones.lifeSpan();
}

请注意，您还需要正确处理析构函数、复制构造函数和赋值运算符（留作练习）。

【讨论】：

非常感谢，您的最佳解决方案解决了当前的问题（教授似乎打算让我这样做）。正如你提到的，我现在正在尝试使用构造函数等。

【解决方案4】：

类星球大战 { 私人的：结构数据克隆 { 整数 ID，时间计数器；字符串名称； };

public:
    StarWars()
    {
        warrior = new data_clone[4];
    }
    ~StarWars()
    {
        delete[] warrior;
    }
    int totalNumber;

    data_clone *warrior;
    void createClone()
    {
        cout << "How many clone warriors do you want to create in total?" << endl;
        cin >> totalNumber;
    }
    void input(struct data_clone *pointer, int total)
    {

        for(int i = 0; i < total; i++)
        {
            cout << "For warrior number " << i << ":" << endl;
            cout << "What is the warrior's name?" << endl;
            cin >> pointer[i].name;
            cout << "What is the warrior's ID number?" << endl;
            cin >> pointer[i].ID;
            cout << "What is the warrior's time counter?" << endl;
            cin >> pointer[i].timeCounter;
        }
    }
    void lifeSpan(struct data_clone *pointer, int total)
    {
        for(int i = 0; i < total; i++)
        {
            cout << "Warrior number " << pointer[i].name << ": " << endl;
            while(pointer[i].timeCounter > 0)
            {
                cout << "Warrior name: " << pointer[i].name << endl;
                cout << "Warrior ID number: " << pointer[i].ID << endl;
                cout << "Warrior time counter: " << pointer[i].timeCounter << endl;
                cout << "Clone is alive." << endl;
                pointer[i].timeCounter--;
            }
            cout << "Warrior name: " << pointer[i].name << endl;
            cout << "Warrior ID number: " << pointer[i].ID << endl;
            cout << "Warrior time counter: " << pointer[i].timeCounter << endl;
            cout << "Clone is dead." << endl;
        }
    }

};

注意：我只是硬编码，这不是正确的方法，它迫使你只输入 4 种类型的数据克隆 "战士 = 新数据克隆[4]；"

你至少会得到你的结果

【讨论】：

考虑到这是 OP 对 C++ 的第一次分配，他们很可能不熟悉 new/delete 以及 C++ 中分配内存的优点/缺点，你的答案应该更好地详细说明这一点，而不是给他们更多要复制的内容。