C++面向对象的问题

Question

我正在尝试学习 C++ OOP，我编写了以下代码:

main.cpp

#include <iostream>
#include <string>
#include "monster.h"
using namespace std;

int main(int argc, char** argv) {
    Monster monster("Wizard",150,50);
    Monster monster2("Gorgoyle",450,15);

    cout << monster2.getHealth() << endl;
    monster.attack(monster2);
    cout << monster2.getHealth() << endl;
}

怪物.h

#ifndef MONSTER_H
#define MONSTER_H
#include <iostream>
#include <string>
using namespace std;

class Monster
{
public:
    Monster(string name_, int health_, int damage_);
    ~Monster();
    int attack(Monster opponet);
    int getHealth();
    string name;
    int damage;
    int health = 0;
    int getDamage();
    void setHealth(int health_);
    void setDamage(int damage_);
    void setName(string name);
    void doDamageToOpponent(Monster opponent);
    string getName();
};

#endif

怪物.cpp

#include "monster.h"

Monster::Monster(string name_, int health_, int damage_) {
    health = health_;
    setDamage(damage_);
    setName(name_);
}

Monster::~Monster() { }

int Monster::attack(Monster opponent) {
    doDamageToOpponent(opponent);
}

void Monster::doDamageToOpponent(Monster opponent) {
    int newHealth = opponent.getHealth() - this->getDamage();
    opponent.setHealth(newHealth);
}

int Monster::getHealth() {
    return health;
}

int Monster::getDamage() {
    return damage;
}

void Monster::setHealth(int health_) {
    health = health_;   
}

void Monster::setDamage(int damage_) {
    this->damage = damage_;
}

void Monster::setName(string name_) {
    this->name = name_;
}

string Monster::getName() {
    return name;
}

现在我的问题是，当我运行这段代码时，我希望 monster2 对象有 400 点生命值，但它仍然是 450 :S

必须在这里做什么才能做到这一点？我注意到它在 doDamageToOppoenet 中可以是 400，但是当它离开那个 block 时，它仍然是 450。请帮助我!谢谢。

Answer 1

您正在按值传递对象:

void Monster::doDamageToOpponent(Monster opponent) <- This should be by reference
int Monster::attack(Monster opponent) <- idem

这意味着:您正在创建 Monster 对象的新拷贝，您打算在调用的函数中对其造成伤害，然后实际处理该拷贝的伤害但留下原始 < strong>旧的对象，其值未被修改。

以下签名可以代替:

void Monster::doDamageToOpponent(Monster& opponent)
int Monster::attack(Monster& opponent)

如果您想了解更多相关信息，请继续阅读:Passing stuff by reference和 Passing stuff by value