如何重载这些运算符以使该程序正常工作？

Question

为简单起见，这是我的课堂作业：将以下函数添加到 Cspinner 类中。

重载等号以比较两个微调器。如果 w1、w2 和 w3 是微调器，则以下指令应该是有效的。

if ( w1 == w2 && w2 == w3)     cout << "You win!";

重载等号以比较微调器和水果（字符数组）。以下指令应该是有效的。

if (w1 == "Apple") cout << "Spinner is a Apple.";

重载输出 (

cout << w1 << endl;

重载类中的一个函数！！

void main()
{
        Cspinner w1;
        Cspinner w2;
        Cspinner w3(80,5,5,5,5);
        for (int x=0;x<=9;x++)
        {
                w1.spin();
                w2.spin();
                w3.spin();
                cout << w1 << " " << w2 << " " << w3;
                if (w1 == w2 && w2 == w3)
                {
                    if (w1 == "Apple")    cout << "  (All Apples) ";
                    else if (w1== "Orange") cout << "  (All Oranges) ";
                    else if (w1== "Cherry") cout << "  (All Cherries) ";
                    else if (w1== "Banana") cout << "  (All Bananas) ";
                    else  cout << "  (All Peaches)";
                }

                cout << endl;
        }
}

上述程序的示例输出。

橙苹果苹果 桃 香蕉 苹果 香蕉 苹果 苹果 橙橙苹果 香蕉 樱桃 苹果 橙橙橙（全橙） 橙色 苹果 苹果 桃 苹果 苹果 橘子 苹果 桃子 苹果樱桃苹果

这是我的代码，我只是不知道如何重载运算符，我将不胜感激任何解释这件事。谢谢！

#include <iostream>

using namespace std;

class Cspinner
{
    friend void operator << (ostream& left, Cspinner Result);
    int apple;
    int orange;
    int cherry;
    int banana;
    int peach;

    string Result = "Not rolled! ";

public:
    Cspinner()
    {
        apple = 30;
        orange = apple + 25;
        cherry = orange + 20;
        banana = cherry + 15;
        peach = banana + 10;
    }

    Cspinner(int AppleChance, int OrangeChance, int CherryChance, int BananaChance, int PeachChance)
    {
        apple = AppleChance;
        orange = apple + OrangeChance;
        cherry = orange + CherryChance;
        banana = cherry + BananaChance;
        peach = banana + PeachChance;
    }

    void spin()
    {
        int RandomNumber = (rand() % 100) + 1;

        if (RandomNumber <= apple)
        {
            Result = "Apple ";
        }
        else if (RandomNumber <= orange)
        {
            Result = "Orange ";
        }
        else if (RandomNumber <= cherry)
        {
            Result = "Cherry ";
        }
        else if (RandomNumber <= banana)
        {
            Result = "Banana ";
        }
        else if (RandomNumber <= peach)
        {
            Result = "Peach ";
        }
      
        }
    bool operator == (char fruit) {
        return fruit;
    }
    bool operator == (Cspinner right) {
        return Result == right && left == right;
    }
    };

//void operator << (ostream left, Cspinner Right) {
//    return left, Right;
//}

void main()
{
    srand(time(NULL));

    Cspinner w1;
    Cspinner w2;
    Cspinner w3(80, 5, 5, 5, 5);

    for (int x = 0;x <= 9;x++)
    {
        w1.spin();
        w2.spin();
        w3.spin();

        cout << w1 << " " << w2 << " " << w3;
        if (w1 == w2 && w2 == w3)
        {
            if (w1 == "Apple")    cout << "  (All Apples) ";
            else if (w1 == "Orange") cout << "  (All Oranges) ";
            else if (w1 == "Cherry") cout << "  (All Cherries) ";
            else if (w1 == "Banana") cout << "  (All Bananas) ";
            else  cout << "  (All Peaches)";
    
        }
        cout << endl;
    }
    system("pause");
}

Answer 1

您需要记住的主要一点是，当您在 C++ 中重载类运算符时，参数的左侧是隐含的 this。也就是说，参数的左边是类的 this 实例。比如下面这个小程序。

#include <iostream>

using namespace std;

class Wrapper {
public:
    int someVal;

    Wrapper() { this->someVal = 0; }
    Wrapper(int someVal) { this->someVal = someVal;}

    bool operator < (const Wrapper &w) const {
        return this->someVal < w.someVal;
    }
};

int main() {
    Wrapper w1;
    Wrapper w2(42);

    if (w1 < w2) {
        cout << "W1 is smaller." << endl;
    } else {
        cout << "W2 is smaller." << endl;
    }
}

运行此程序会产生“W1 更小”。

现在，我假设您要与等价运算符 == 比较的是存储在 Result 变量中的值。在这种情况下，重载运算符的代码是：

bool operator == (const Cspinner &c) const {
    return this->Result == c.Result;
}

这是说我想将存储在 this Cspinner 实例的 Result 变量中的值与 Result 的值进行比较strong> 存储在实例const Cspinner &c

类似地，要测试 Cspinner 实例与字符串的相等性，可以像下面这样重载相等运算符。

bool operator == (const string &s) const {
    return this->Result == s;
}

由于存储在this->Result 中的变量是字符串类型，重载的== 将使用字符串类的相等运算符进行比较。