c ：算術運算子多載

我有一個名為HealthPointshas hpand max_hpmembers 的類。我想多載 運算子，所以它會像這樣作業：

HealthPoints healthPoints1;
healthPoints1 -= 150; /* healthPoints1 now has 0 points out of 100 */
HealthPoints healthPoints2(150);
healthPoints2 -= 160; /* healthPoints2 now has 0 points out of 150 */
healthPoints2 = healthPoints1   160; /* healthPoints2 now has 100 points out of 100 */

我成功地使它作業，但只是以特定的順序。如果我把數字放在物件之前，有沒有辦法讓它識別它們兩者之間的數字并采取相應的行動？目前它的作業方式，我知道healthPoints2現在有 160 分（滿分 160 分）。

HealthPoints班級：

class HealthPoints {
    public:
        static const int DEFAULT_MAXHP=100;
        static const int DEFAULT_HP=100;
        static const int MINIMUM_MAXHP=1;
        static const int MINIMUM_HP=0;
        explicit operator int() const;
        HealthPoints(int maxHP=HealthPoints::DEFAULT_MAXHP);
        ~HealthPoints() = default; // Destructor set to default
        HealthPoints(const HealthPoints&) = default; // Copy Constructor set to default
        HealthPoints& operator=(const HealthPoints&) = default; // Assignment operator set to default
        HealthPoints& operator =(const HealthPoints& HP);
        HealthPoints& operator-=(const HealthPoints& HP);
        class InvalidArgument {};
    private:
        int m_maxHP;
        int m_HP;
        friend bool operator==(const HealthPoints& HP1, const HealthPoints& HP2);
        friend bool operator<(const HealthPoints& HP1, const HealthPoints& HP2);
        friend std::ostream& operator<<(std::ostream& os, const HealthPoints& HP);
};

HealthPoints::HealthPoints(int maxHP) {
    if(maxHP < HealthPoints::MINIMUM_MAXHP) {
        throw HealthPoints::InvalidArgument();
    }
    this->m_maxHP=maxHP;
    this->m_HP=m_maxHP;
}

HealthPoints operator (const HealthPoints& HP1, const HealthPoints& HP2) {
    return HealthPoints(HP2) =HP1;
}

HealthPoints operator-(const HealthPoints& HP1, const HealthPoints& HP2) {
    return HealthPoints(HP1)-=HP2;
}

HealthPoints& HealthPoints::operator =(const HealthPoints& HP) {
    if(this->m_HP HP.m_HP>this->m_maxHP) {
        this->m_HP=this->m_maxHP;
    } else {
        this->m_HP =HP.m_HP;
    }
    return *this;
}

HealthPoints& HealthPoints::operator-=(const HealthPoints& HP) {
    if(this->m_HP-HP.m_HP>HealthPoints::MINIMUM_HP) {
        this->m_HP-=HP.m_HP;
    } else {
        this->m_HP=HealthPoints::MINIMUM_HP;
    }
    return *this;
}

uj5u.com熱心網友回復：

在本宣告中：

healthPoints2 = healthPoints1 160;

您的 操作員正在創建一個新HealthPoints物件，該物件是 的副本healthPoints1，因此該物件的m_maxHP設定為100。然后你添加160到那個物件，增加它m_HP但保留它的m_maxHP. 然后，您將該物件分配給healthPoints2，同時復制m_HP和m_maxHP值。這就是 的m_maxHP由healthPoints2變為的150原因100。

在本宣告中：

healthPoints2 = 160 healthPoints1;

您的 操作員正在創建一個設定為的新HealthPoints物件。然后你添加到那個物件，增加它但保留它的. 然后，您將該物件分配給，同時復制和值。這就是 的由變為的原因。m_maxHP160healthPoints1m_HPm_maxHPhealthPoints2m_HPm_maxHPm_maxHPhealthPoints2150160

如果您希望您operator的 s 僅更新m_HP而不更改m_maxHP，則需要添加接受int值而不是HealthPoints物件的多載，例如：

HealthPoints& HealthPoints::operator =(int value) {
    m_HP = std::min(m_HP   value, m_maxHP);
    return *this;
}

HealthPoints& HealthPoints::operator-=(int value) {
    m_HP = std::max(m_HP - value, HealthPoints::MINIMUM_HP);
    return *this;
}

HealthPoints operator (const HealthPoints& HP, int value) {
    return HealthPoints(HP)  = value;
}

HealthPoints operator (int value, const HealthPoints& HP) {
    return HealthPoints(HP)  = value;
}

HealthPoints operator-(const HealthPoints& HP, int value) {
    return HealthPoints(HP) -= value;
}

HealthPoints operator-(int value, const HealthPoints& HP) {
    return HealthPoints(HP) -= value;
}

然后，將HealthPoints(int)建構式標記為在將值傳遞給期望物件的引數explicit時避免不必要的隱式轉換。intHealthPoints

uj5u.com熱心網友回復：

我不完全確定您HealthPoints課程的邏輯，因此請仔細檢查下面的代碼。不過，我的觀點是實施：

    friend HealthPoints operator (const HealthPoints& other, int value);
    friend HealthPoints operator (int value, const HealthPoints& other);

您實際上只需要實作第一個，并讓第二個使用它：

HealthPoints operator (const HealthPoints& hp, int value) {
    HealthPoints ret{hp};
    ret.m_HP = std::min(ret.m_maxHP, ret.m_HP   value);
    return ret;
}
HealthPoints operator (int value, const HealthPoints& hp) {
    return hp   value;
}

你可以在這里看到它的實際效果：

[演示]

int main() {
    HealthPoints hp1{100};
    hp1 -= 50;
    std::cout << "hp1: " << hp1 << "\n";
    auto hp2{hp1   10};
    std::cout << "hp2: " << hp2 << "\n";
    auto hp3{10   hp2};
    std::cout << "hp3: " << hp3 << "\n";
}

// Outputs:
//   hp1: (max_HP = 100, HP = 50)
//   hp2: (max_HP = 100, HP = 60)
//   hp3: (max_HP = 100, HP = 70)

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