为什么我不能在 C++ 中更新我的类属性？

Question

我正在制作一个向导游戏原型，但遇到了一个问题：

我创建了一个名为 Wizard 的类和一个名为 Goblin 的类：

class Wizard
{
    public:
        int damage;
        int health;
        int stamina;

        Wizard(int d, int h, int s)
        {
            d = damage;
            h = health;
            s = stamina;
        }

        float getDamage() { return damage; }
        void setDamage(int v) { v = damage; }

        float getHealth() { return health; }
        void setHealth(int v) { v = health; }

        float getStamina() { return stamina; }
        void setStamina(float v) { v = stamina; }

};

class Goblin
{
    public:
        int health;
        int damage;

        Goblin(int h, int d)
        {
            h = health;
            d = damage;
        }

        float getHealth() { return health; }
        void setHealth(int v) { v = health; }

        float getDamage() { return damage; }
        void setDamage(int v) { v = damage; }
};

然后，我为它们声明并初始化变量：

Wizard wizard(50, 150, 10);
Goblin goblin(150, 25);

然后，我创建了一个attack() 函数：

void attack(Wizard attacker, Goblin target)
{
    if(target.getDamage() > 0.0)
    {
        attacker.setStamina(attacker.getStamina() - 1);
    }
}

所以，在主函数中，我调用了attack并打印出结果：

int main()
{
    attack(wizard, goblin);
    printInfo();

    return 0;
}

但结果是这样的：

> clang++-7 -pthread -std=c++17 -o main main.cpp
> ./main
Wizard Health: 0
Wizard Damage: 0
Wizard Stamina: 0

Goblin Damage: 0
Goblin Health: 0

我还创建了一个printInfo() 函数：

void printInfo()
{
    std::cout << "Wizard Health: " << wizard.getHealth() << std::endl;
    std::cout << "Wizard Damage: " << wizard.getDamage() << std::endl;
    std::cout << "Wizard Stamina: " << wizard.getStamina() << std::endl;
    
    std::cout << std::endl;

    std::cout << "Goblin Damage: " << goblin.getHealth() << std::endl;
    std::cout << "Goblin Health: " << goblin.getDamage() << std::endl;
}

如果你需要，这里是完整的文件：

#include <iostream>

class Wizard
{
    public:
        int damage;
        int health;
        int stamina;

        Wizard(int d, int h, int s)
        {
            d = damage;
            h = health;
            s = stamina;
        }

        float getDamage() { return damage; }
        void setDamage(int v) { v = damage; }

        float getHealth() { return health; }
        void setHealth(int v) { v = health; }

        float getStamina() { return stamina; }
        void setStamina(float v) { v = stamina; }

};

class Goblin
{
    public:
        int health;
        int damage;

        Goblin(int h, int d)
        {
            h = health;
            d = damage;
        }

        float getHealth() { return health; }
        void setHealth(int v) { v = health; }

        float getDamage() { return damage; }
        void setDamage(int v) { v = damage; }
};

Wizard wizard(50, 150, 10);
Goblin goblin(150, 25);

void attack(Wizard attacker, Goblin target);
void printInfo();

int main()
{
    attack(wizard, goblin);
    printInfo();

    return 0;
}

void attack(Wizard attacker, Goblin target)
{
    if(target.getDamage() > 0.0)
    {
        attacker.setStamina(attacker.getStamina() - 1);
    }
}

void printInfo()
{
    std::cout << "Wizard Health: " << wizard.getHealth() << std::endl;
    std::cout << "Wizard Damage: " << wizard.getDamage() << std::endl;
    std::cout << "Wizard Stamina: " << wizard.getStamina() << std::endl;
    
    std::cout << std::endl;

    std::cout << "Goblin Damage: " << goblin.getHealth() << std::endl;
    std::cout << "Goblin Health: " << goblin.getDamage() << std::endl;
}

很抱歉，如果这很长，但我们将不胜感激。

Answer 1

您的attack() 函数按值接受参数。因此，它会修改您的全局变量的副本。

使用参考：

void attack(Wizard& attacker, Goblin& target)
{
    ...
}

PS：另见 https://en.cppreference.com/w/cpp/language/constructor 了解成员初始化列表

Answer 2

在您的构造函数和 set* 方法中，您需要将输入参数值分配给类的成员变量。反之亦然。

#include <iostream>

class Wizard
{
    public:
        int damage;
        int health;
        int stamina;

        Wizard(int d, int h, int s)
        {
            damage = d;
            health = h;
            stamina = s;
        }

        float getDamage() { return damage; }
        void setDamage(int v) { damage = v; }

        float getHealth() { return health; }
        void setHealth(int v) { health = v; }

        float getStamina() { return stamina; }
        void setStamina(float v) { stamina = v; }

};

class Goblin
{
    public:
        int health;
        int damage;

        Goblin(int h, int d)
        {
            health = h;
            damage = d;
        }

        float getHealth() { return health; }
        void setHealth(int v) { health = v; }

        float getDamage() { return damage; }
        void setDamage(int v) { damage = v; }
};

Wizard wizard(50, 150, 10);
Goblin goblin(150, 25);

void attack(Wizard attacker, Goblin target);
void printInfo();

int main()
{
    attack(wizard, goblin);
    printInfo();

    return 0;
}

void attack(Wizard attacker, Goblin target)
{
    if(target.getDamage() > 0.0)
    {
        attacker.setStamina(attacker.getStamina() - 1);
    }
}

void printInfo()
{
    std::cout << "Wizard Health: " << wizard.getHealth() << std::endl;
    std::cout << "Wizard Damage: " << wizard.getDamage() << std::endl;
    std::cout << "Wizard Stamina: " << wizard.getStamina() << std::endl;
    
    std::cout << std::endl;

    std::cout << "Goblin Damage: " << goblin.getHealth() << std::endl;
    std::cout << "Goblin Health: " << goblin.getDamage() << std::endl;
}