Question

我已将父类的成员函数设为public。但我仍然收到错误

no＆＃39; void MotorBike :: speeddown（）＆＃39;在课程＆＃39; MotorBike＆＃39;
中声明的成员函数

speedup和speeddown。即使我公开继承了父类。

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

class Bicycle
{
protected:
    int speed;
    char color[8];
public:
    Bicycle(int, char*);
    void speedup();
    void speeddown();
    void turnLeft();
    void turnRight();
};

class MotorBike:public Bicycle
{
private:
    int currentGear;
    int currentFuel;
public:
    MotorBike(int,char*,int,int);

};

Bicycle::Bicycle(int Speed,char* Color)
{
    speed=Speed;
    strcpy(color,Color);
    cout<<"The bike is now moving north!"<<endl;
}

MotorBike::MotorBike(int Speed,char* Color,int CurrentGear,int CurrentFuel): Bicycle(speed,color)
{
    speed=Speed;
    strcpy(color,Color);
    currentGear=CurrentGear;
    currentFuel=CurrentFuel;
    cout<<"The motorbike is now moving north!"<<endl;
}

void Bicycle::speedup()//error line
{
    cout<<"Speed is increased!"<<endl;
    speed+=1;
}

void Bicycle::speeddown()//error line
{
    if(speed>1)
    {
        cout<<"Speed is decreased!"<<endl;
        speed-=1;
    }
    else
        cout<<"The bike is already at rest!"<<endl;

}

void MotorBike::speedup()//error line
{
    if(currentGear==4)
        cout<<"You are already at maximum speed!"<<endl;
    else
    {
        switch(currentGear)
        {
        case 0:
            currentGear=1;
            currentFuel-=0.01;
            speed+=0.25;
            break;
        case 1:
            currentGear=2;
            currentFuel-=0.02;
            speed+=0.5;
            break;
        case 2:
            currentGear=3;
            currentFuel-=0.03;
            speed+=0.75;
            break;
        case 3:
            currentGear=4;
            currentFuel-=0.04;
            speed+=1;
            break;

        }
    }
}

void MotorBike::speeddown()//error line
{
    if(speed==1||speed>1)
    speed-=1;
    else
        cout<<"You are already at minimum speed!"<<endl;
}

int main()
{
    Bicycle B1(0,"Black");
    MotorBike MB1(0,"Black",0,100);
}

Answer 1

您的speedup没有功能speeddown或MotorBike。如果你想要，你必须在class MotorBike:public Bicycle { private: int currentGear; int currentFuel; public: MotorBike(int,char*,int,int); void speedup(); void speeddown(); };类中声明它，比如

rowattr

Answer 2

我将在这个问题上自上而下：

将已弃用的#include <string.h>更改为#include <string>。

你的自行车具有无定义的功能，如果有人试图调用它们，将产生LNK2019（未解析的外部）。定义它们，删除它们，或使Bicycle成为一个抽象类。自行车也有孩子，所以给它一个虚拟的析构函数。

Bicycle(int, char*);
virtual ~Bicycle() = default;
virtual void speedup();
virtual void speeddown();
virtual void turnLeft();
virtual void turnRight();

您正在定义属于MotorBike成员的函数，但您从未声明过它们。将它们添加到MotorBike的声明中：

class MotorBike:public Bicycle
{
private:
    int currentGear;
    int currentFuel;
public:
    Motorbike(int,char*,int,int);
    void speedup();
    void speeddown();
};

在摩托车中覆盖自行车功能时使用override关键字：

class MotorBike:public Bicycle
{
private:
    int currentGear;
    int currentFuel;
public:
    Motorbike(int,char*,int,int);
    void speedup() override;  // like this
    void speeddown() override;  // and this
};

或者，或者，使用Bike在MotorBike中实现的任何默认功能：

class MotorBike:public Bicycle
{
private:
    int currentGear;
    int currentFuel;
public:
    Motorbike(int,char*,int,int);
    using Bicycle::speedup;  // like this
    using Bicycle::speeddown;  // and this
};

修复您的数据类型。 MotorBike将currentGear和currentFuel声明为整数，但在MotorBike::speedup中，您可以向它们添加浮点值。这不起作用，因为这些值的小数部分将被截断。

如何使用继承定义父类的功能？

2 个答案: