我有Shape类，从中继承了5个不同的类（在不同的文件中）。在覆盖所有不同类中的所有纯虚函数之后，我得到此错误：'Shape': cannot instantiate abstract class，它不会告诉我错误的出处。这是Shape类：
#pragma once
#include "Point.h"
#include "Canvas.h"
#include <string>
class Shape
{
public:
Shape(const std::string& name, const std::string& type);
virtual double getArea() const = 0;
virtual double getPerimeter() const = 0;
virtual void draw(const Canvas& canvas) = 0;
virtual void move(const Point& other) = 0; // add the Point to all the points of shape
void printDetails() const;
std::string getType() const;
std::string getName() const;
virtual void clearDraw(const Canvas& canvas) = 0;
protected:
std::string _name;
std::string _type;
};
这是从Shape继承的2个类的示例：
class Circle : public Shape
{
Point _center;
double _radius;
public:
Circle(const Point& center, double radius, const std::string& type, const std::string& name);
~Circle();
const Point& getCenter() const;
double getRadius() const;
virtual void draw(const Canvas& canvas);
virtual void clearDraw(const Canvas& canvas);
// override functions if need (virtual + pure virtual)
virtual void move(const Point& other);
virtual double getArea() const;
virtual double getPerimeter() const;
};
而且我怀疑问题出在这个类上，在这个类中，我将函数保持纯虚拟的，因为其他类也从该类继承，并且它们需要不同的实现：
#include "Shape.h"
#include "Point.h"
#include <vector>
class Polygon : public Shape
{
public:
Polygon(const std::string& type, const std::string& name);
virtual ~Polygon();
// override functions if need (virtual + pure virtual)
virtual void move(const Point& other);
virtual double getArea() const = 0;
virtual double getPerimeter() const = 0;
virtual void draw(const Canvas& canvas) = 0;
virtual void clearDraw(const Canvas& canvas) = 0;
protected:
std::vector<Point> _points;
};
这里是代码中我认为可能会发生错误的部分：
if (optionChosen == 0) // Circle
{
double x = 0;
double y = 0;
double radius = 1.0;
std::string name;
std::cout << "Please enter X: " << std::endl;
std::cin >> x;
std::cout << "Please enter Y: " << std::endl;
std::cin >> y;
do
{
std::cout << "Please enter radius: " << std::endl;
std::cin >> radius;
if (radius < 1)
{
std::cout << "Invalid radius... Try again" << std::endl;
}
// If radius is invalid this code will run again
} while (radius < 1);
std::cout << "Enter the name of the shape: " << std::endl;
std::cin >> name;
const Point& center = Point(x, y);
// Create a new circle and push it to the vector
Circle circle = Circle::Circle(center, radius, "Circle", name); // Circle inherits from Shape
_shapes.push_back(circle);
}
else if (optionChosen == 1) // Arrow
{
double point1[2] = { 0 };
double point2[2] = { 0 };
std::string name;
std::cout << "Enter the X of point number: 1" << std::endl;
std::cin >> point1[0];
std::cout << "Enter the Y of point number: 1" << std::endl;
std::cin >> point1[1];
std::cout << "Enter the X of point number: 2" << std::endl;
std::cin >> point2[0];
std::cout << "Enter the Y of point number: 2" << std::endl;
std::cin >> point2[1];
std::cout << "Enter the name of the shape: " << std::endl;
std::cin >> name;
const Point& Point1 = Point(point1[0], point1[1]);
const Point& Point2 = Point(point2[0], point2[1]);
// Create a new arrow and push it to the vector
Arrow arrow = Arrow::Arrow(Point1, Point2, "Arrow", name); // Arrow inherits from polygon
_shapes.push_back(arrow);
}
else if (optionChosen == 2) // Triangle
{
double point1[2] = { 0 };
double point2[2] = { 0 };
double point3[2] = { 0 };
std::string name;
std::cout << "Enter the X of point number: 1" << std::endl;
std::cin >> point1[0];
std::cout << "Enter the Y of point number: 1" << std::endl;
std::cin >> point1[1];
std::cout << "Enter the X of point number: 2" << std::endl;
std::cin >> point2[0];
std::cout << "Enter the Y of point number: 2" << std::endl;
std::cin >> point2[1];
std::cout << "Enter the X of point number: 3" << std::endl;
std::cin >> point3[0];
std::cout << "Enter the Y of point number: 3" << std::endl;
std::cin >> point3[1];
std::cout << "Enter the name of the shape: " << std::endl;
std::cin >> name;
const Point& Point1 = Point(point1[0], point1[1]);
const Point& Point2 = Point(point2[0], point2[1]);
const Point& Point3 = Point(point3[0], point3[1]);
// Create a new triangle and push it to the vector
Triangle triangle = Triangle::Triangle(Point1, Point2, Point3, "Triangle", name); // Triangle inherits from Polygon
_shapes.push_back(triangle);
}
else if (optionChosen == 3) // Rectangle
{
double topLeftCorner[2] = { 0 };
double length = 0;
double width = 0;
std::string name;
std::cout << "Enter the X of the left corner: " << std::endl;
std::cin >> topLeftCorner[0];
std::cout << "Enter the Y of the left corner: " << std::endl;
std::cin >> topLeftCorner[1];
std::cout << "Please enter the length of the shape: " << std::endl;
std::cin >> length;
std::cout << "Please enter the width of the shape: " << std::endl;
std::cin >> width;
std::cout << "Enter the name of the shape: " << std::endl;
std::cin >> name;
const Point& point = Point(topLeftCorner[0], topLeftCorner[1]);
// Create a new rectangle and push it to the vector
myShapes::Rectangle rectangle = myShapes::Rectangle(point, length, width, "Rectangle", name); // Rectangle inherits from Polygon
_shapes.push_back(rectangle);
}
如果有人可以帮助我找到问题，我会很高兴。
您无法将对象Shape存储在向量中，因为它包含纯虚函数。您可以将指针存储在向量中，也可以将指针存储在智能指针中，并适当地创建子类。
std::vector<Shape*> _shapes;
//…
_shapes.push_back( new Circle( … ) );
或
std::vector<std::unique_ptr<Shape>> _shapes;
//…
_shapes.push_back( std::make_unique<Circle>( center, radius, "Circle", name ) );
[另外，使用继承时，我建议使用override关键字。因此，例如在您的Circle类中，您将有
void move(const Point& other) override;