Question

我是C ++的新手，并且遇到了一些问题。我想创建一个抽象类，以及从该类继承的两个更抽象的类。最后，这两个类用于由具体类实现。这是我的标题和源文件：

/*
 * Cylinder.h
 */

#ifndef CYLINDER_H_
#define CYLINDER_H_

class Shape{
public:
    virtual ~Shape();
    virtual const double area()=0;
    virtual const void printDetails();

};

class Shape2D: virtual public Shape{
public:
    virtual const double scope()=0;
};

class Shape3D: virtual public Shape{
public:
    virtual const double volume()=0;
};

class Rectangle: public Shape2D{
private:
    double a;
    double H;

public:
    Rectangle();
    Rectangle(double a, double H);
    Rectangle(Rectangle &r);

    double getA() const;
    double getH() const;
    void setA(double a);
    void setH(double H);

};

class Circle: public Shape2D{
private:
    double r;

public:
    Circle();
    Circle(double r);
    Circle(Circle &c);

    double getR() const;
    void setR(double r);
};

class Cylinder: public Shape3D{
private:
    Circle base;
    Rectangle wrapper;

public:
    Cylinder();
    Cylinder(Rectangle &r, Circle &c);
    Cylinder(double a, double H, double r);
    Cylinder(Cylinder &c);

    double getHeight() const;
    double getBaseRadius() const;
    double getBaseArea() const;
    double getBaseScope() const;
    double getWrapperArea() const;
    double getWrapperScope() const;

    void setHeight(double H);
    void setRadius(double r);

    Rectangle* getWrapper() const;
    Circle* getBase() const;
};


#endif /* CYLINDER_H_ */


/*
 * Cylinder.cpp
 */

#include <iostream>
#include "Cylinder.h"
#include <math.h>
using namespace std;

void Shape2D::printDetails() const{
    cout<<"\nArea: "<<area();
    cout<<"\nScope: "<<scope();
}

void Shape3D::printDetails() const{
    cout<<"\nArea: "<<area();
    cout<<"\nVolume: "<<volume();

}

Rectangle::Rectangle(){
        H=0.0;
        a=0.0;
}

Rectangle::Rectangle(double a, double H){
        this->H=H;
        this->a=a;
}

Rectangle::Rectangle(Rectangle &r){
        a=r.a;
        H=r.H;
}

Rectangle::~Rectangle(){
    cout<<"Rectangle deallocated.";
}

double Rectangle::getA() const{
    return a;
}

double Rectangle::getH() const{
    return H;
}

void Rectangle::setA(double a){
    this->a=a;
}

void Rectangle::setH(double H){
    this->H=H;
}

double Rectangle::scope() const{
    return 2*a+2*H;
}

double Rectangle::area() const{
        return a*H;
}

void Rectangle::printDetails() const{
    cout<<"\nDimensions of rectangle: "<<a<<"*"<<H;
    Shape::printDetails();
}

Circle::Circle(){
    r=0.0;
}

Circle::Circle(double r){
    this->r=r;
}

Circle::Circle(Circle &c){
    r=c.r;
}

Circle::~Circle(){
    cout<<"Circle deallocated.";
}

double Circle::getR() const{
    return r;
}

void Circle::setR(double r){
    this->r=r;
}

double Circle::scope() const{
    return 2*r*M_PI;
}

double Circle::area() const{
    return r*r*M_PI;
}

void Circle::printDetails() const{
    cout<<"\nRadius of circle: "<<r;
    Shape::printDetails();
}

Cylinder::Cylinder(){
    wrapper=new Rectangle(0.0,0.0);
        base=new Circle(0.0);

}

Cylinder::Cylinder(Rectangle &r, Circle &c){
    base=c;
    wrapper=r;
}

Cylinder::Cylinder(double a=0.0, double H=0.0, double r=0.0){
    wrapper=new Rectangle(a,H);
    base=new Circle(r);
}

Cylinder::Cylinder(Cylinder &c){
    c.base=new Circle(c.base);
    c.wrapper=new Rectangle(c.wrapper);
}

Cylinder::~Cylinder(){
    delete base;
    delete wrapper;
}
double Cylinder::getHeight() const{
    return wrapper.getH();
}

double Cylinder::getBaseRadius() const{
    return base.getR();
}

double Cylinder::getBaseArea() const{
    return base.area();
}

double Cylinder::getBaseScope() const{
    return base.scope();
}

double Cylinder::getWrapperArea() const{
    return wrapper.area();
}

double Cylinder::getWrapperScope() const{
    return wrapper.scope();
}

void Cylinder::setHeight(double H){
    wrapper.setH(H);
}
void Cylinder::setRadius(double r){
    base.setR(r);
    wrapper.setA(2*base.getR()*M_PI);
}

double Cylinder::volume() const{
    return base*wrapper.getH();
}

double Cylinder::area() const{
    return 2*base.area+wrapper.area;
}

void Cylinder::printDetails() const{
    cout<<"\nRadius of base of Cilynder: "<<base.getR();
    cout<<"\nHeight of wrapper: "<<wrapper.getH();
    Shape::printDetails();
}

Rectangle* Cylinder::getWrapper() const{
    return new Rectangle(wrapper);
}

Circle* Cylinder::getBase() const{
    return new Circle(base);
}

我的编译器给了我不同的错误，因为我尝试修改代码以某种方式完成将Rectangle，Circle和Cylinder作为非抽象类。我不知道我应该在哪里放置方法定义（如果它们在继承的类中重复），实际上它们的形式是什么。抱歉，长文字。我希望有一个人可以帮助我。提前致谢

萨姆

Answer 1

您没有实现纯虚方法。只要你有纯虚方法（virtual void whatever()=0），就会使类抽象化。抽象类无法实例化。为了实例化，具体的子类必须实现祖先类中的所有纯虚方法。

例如，Rectangle缺少从scope继承的Shape2D方法，以及从area继承的Shape方法。这将导致错误“无法实例化Rectangle类，因为它是抽象的。”看起来你在文件中有较低的那些方法的实现，但它们没有在任何地方声明在Rectangle类中。

具有虚函数的C ++继承层次结构

1 个答案: