如何更新对象的属性？

Question

我有一个Aircraft 课程。我想循环更新飞机对象的属性（每隔一秒）。

如何在不创建新对象的情况下更新这些属性？我应该使用指针吗？我的目标：每秒钟更新一次飞机信息

我的代码：

class Aircraft
{
public:
    unsigned int altitude, speed, direction;

    Aircraft(unsigned int aAltitude, unsigned int aSpeed, unsigned int aDirection) 
    {
        altitude = aAltitude;
        speed = aSpeed;
        direction = aDirection;
    }
};

int main()
{
    //aircraft's initial values
    Aircraft myAircraft(0, 10, 345); 
    //Initial values should are printed 
    cout << myAircraft.altitude + "," + myAircraft.speed + "," + myAircraft.direction << endl; //print initial values

    //In this loop new values for altitude, speed and direction should be assigned
    for (int i = 0; i < 10; i++)
    {
        //aircraft's new values
        Aircraft myAircraft(new altitude, new speed, new direction);

        //print updated attributes
        cout << myAircraft.altitude + "," +
                myAircraft.speed "," myAircraft.direction
             << endl << endl; //print new values
    }
}

结果应如下所示：（值无关紧要）

0, 10, 345
0, 30, 345
0, 60, 345
0, 100, 345
0, 150, 345
300, 180, 345
700, 220, 345
2000, 250, 345

Answer 1

如何在不创建新对象的情况下更新这些属性？

在循环外创建Aircraft，使用类的setter functions（建议将类资源设为private），设置类内的各个属性。

我应该使用指针吗？

给出解释，正确地NOT，因为您只想打印类属性中的每个更新，不需要动态内存分配。

关于更新后每次打印元素，正常的C++约定是overload operator<<，方便你写：

std::cout << aircraft_object;

示例代码如下所示：(See Live)

#include <iostream>

using uint32 = unsigned int;
class Aircraft /* final */
{
private: // private attributes
    uint32 altitude, speed, direction;

public:
    // provided default arguments, so that default-construction is possible
    Aircraft(uint32 aAltitude = 0, uint32 aSpeed = 0, uint32 aDirection = 0)
        : altitude{ aAltitude }
        , speed{ aSpeed }
        , direction{ aDirection }
    {}
    // provide setters
    void setAltitude(const uint32 alti) noexcept { altitude = alti; }
    void setSpeed(const uint32 sp) noexcept { speed = sp; }
    void setDirection(const uint32 dir) noexcept { direction = dir; }
    // non-member function(s): operator<< overload
    friend std::ostream& operator<<(std::ostream& out, const Aircraft& obj) noexcept;
};

std::ostream& operator<<(std::ostream& out, const Aircraft& aircraft) noexcept
{
    return out << aircraft.altitude << ", " << aircraft.speed
                                    << ", " << aircraft.direction << '\n';
}

int main()
{
    Aircraft aircraft_obj{}; // constructed with intial values {0, 0,0}

    for (auto i = 0; i < 3; ++i)
    {
        uint32 alti, sp, dir;
        // get the user inputs
        std::cin >> alti >> sp >> dir;
        // set the attributes
        aircraft_obj.setAltitude(alti);
        aircraft_obj.setSpeed(sp);
        aircraft_obj.setDirection(dir);
        // print out the object
        std::cout << aircraft_obj;
    }
    return 0;
}

输入：

0 10 345
0 30 345
0 60 345

输出：

0, 10, 345
0, 30, 345
0, 60, 345

Answer 2

您可以使用. 运算符轻松修改非常量对象值。

myAircraft.altitude  = newAltitude;
myAircraft.speed     = newSpeed;
myAircraft.direction = newDirection;

cout << myAircraft.altitude << ", " << myAircraft.speed << ", " << myAircraft.direction << '\n';

附：通过将字符串与+ 连接来打印字符串是一种非常糟糕的做法。 相反，请使用<< 运算符，如上所示。

在您的情况下，代码甚至无效，因为您尝试添加带有字符串的数字。做你想做的事情的逻辑正确方法是首先将数字转换为字符串to_string(myAircraft.altitude) + ", "。

另外，避免使用endl，因为它会不必要地刷新缓冲区。好处可以在这里看到：Benchmark。