Question

我有一个Aircraft班。我想循环更新飞机对象的属性（每秒钟更新一次）。

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：每隔一秒钟更新飞机信息

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？

在循环外创建一个Aircraft，并使用该类的setter functions（建议将类资源设置为private）来设置该类中的每个属性。

我应该使用指针吗？

为了给出解释，相当不，因为您只想在类属性中打印每个更新，所以不需要动态内存分配。

关于每次更新后打印元素，通常的C ++惯例是 overload operator<< ，这使您可以方便地编写：

std::cout << aircraft_object;

示例代码如下：（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.运算符轻松地修改非常量对象的值。

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

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

P.S。通过将字符串与+连接来打印字符串是一种非常不好的做法。而是使用如上所述的<<运算符。

在您的情况下，该代码甚至无效，因为您正尝试在字符串中添加数字。符合逻辑的正确方法是首先将数字转换为字符串to_string(myAircraft.altitude) + ", "。

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

如何更新对象的属性？

2 个答案: