在派生的 class 中使用重載的 + 運算符

Question

我正在練習從派生類（在我的例子中是飛機）中使用重載賦值運算符，它工作得很好。 我遇到的問題是 + 運算符重載。 它應該只是對兩個 Airplane 對象的 engine_power 和座位求和，然后在求和飛行速度（粗線）之后。 And it really does go to the Base class overloaded + operator function when called from derived class (Vehicle::operator +(rhs);), but then Vehicle variable temp sums everything as it should do, but for some reason calls destructor right after並且我的派生對象的基本 class 屬性保持為 0。期待任何建議或建議

#include <iostream>
using namespace std;

class Vehicle {
protected:
    int engine_power;
    int seats;
public:
    Vehicle(int engine_power, int seats)
        : engine_power{engine_power},seats{seats}{
            cout << "Vehicle constructor" << endl;
        }

    Vehicle &operator=(const Vehicle &rhs){
            cout << "Vehicle assignment" << endl;
        if (this==&rhs) 
            return *this;
        else{
            engine_power=rhs.engine_power;
            seats=rhs.seats;
            return *this;
            }
        }
    Vehicle operator+(const Vehicle &rhs){
        Vehicle temp{0,0};
        temp.engine_power=engine_power+rhs.engine_power;
        temp.seats=seats+rhs.seats;
        return temp;
    }
    ~Vehicle() {
        cout << "Vehicle destructor" << endl;
    }
};

class Airplane : public Vehicle {
private:
    int flying_speed;
public:
    Airplane(int a, int b, int flying_speed)
        : Vehicle{a,b}, flying_speed{flying_speed}{
            cout << "Airplane constructor" << endl;
        }

    Airplane &operator= (const Airplane &rhs){
        cout << "Airplane assignment" << endl;
        if (this!=&rhs){
            Vehicle::operator =(rhs);
            flying_speed=rhs.flying_speed;
            return *this;
        } else
            return *this;
    }
    Airplane operator+ (const Airplane &rhs) {
        Airplane temp{0,0,0};
        **Vehicle::operator +(rhs);**
        **temp.flying_speed=flying_speed+rhs.flying_speed;**
        return temp;
    }
    ~Airplane() {
        cout << "Airplane destructor" << endl;
    }
};

int main(){
Airplane a1 {10,20,30};
Airplane a2 {10,22,33};
Airplane a3 = a1+a2;
return 0;
}

Answer 1

正如評論中所指出的，當在派生的 class 中調用時，您不會存儲基礎 class Vehicle::operator+()的結果。 這是固定代碼：

#include <iostream>
using namespace std;

class Vehicle {
protected:
    int engine_power;
    int seats;
public:
    Vehicle(int engine_power, int seats)
        : engine_power{engine_power},seats{seats}{
            //cout << "Vehicle constructor" << endl;
        }

    Vehicle operator+(const Vehicle &rhs){
        Vehicle temp{0,0};
        temp.engine_power=engine_power+rhs.engine_power;
        temp.seats=seats+rhs.seats;
        return temp;
    }
};

class Airplane : public Vehicle {
private:
    int flying_speed;
public:
    Airplane(int a, int b, int flying_speed)
        : Vehicle{a,b}, flying_speed{flying_speed}{
            //cout << "Airplane constructor" << endl;
        }
    Airplane operator+ (const Airplane &rhs) {
        Airplane temp{0,0,0};
        static_cast<Vehicle&>(temp) = Vehicle::operator +(rhs);
        temp.flying_speed=flying_speed+rhs.flying_speed;
        return temp;
    }
    void print() const {
        cout << " power " << engine_power 
             << " seats " << seats  
             << " speed " << flying_speed 
            << std::endl;
    }
};

int main(){
    Airplane a1 {10,20,30};
    Airplane a2 {10,22,33};
    Airplane a3 = a1+a2;
    a3.print();
    return 0;
}

Output： power 20 seats 42 speed 63

現場演示