Question

我创建了一个程序，它使用虚函数和多态来计算三个不同对象的参数和面积：圆形，矩形和直角三角形。每当我尝试将一个不同的对象类分配给我在测试类中的指针时，它会显示“错误：期望一个类型说明符”：

shape_ptr = new Rectangle;

屏幕截图of error shown

我几乎可以肯定这是一个非常简单的东西，我错过了，但它不是包含头文件，因为我已经在每个班级上完成了这一点而没有任何我能看到的错误。这是我的代码：

基类：

#ifndef SHAPE
#define SHAPE
#include <iostream>
using namespace std;
class Shape {
public:
    virtual void compute_area() = 0; // a pure virtual function
    virtual void compute_perimeter() = 0; // a pure virtual function
    virtual void read_shape_data() = 0; // a pure virtual function
    virtual void print_result() { // a virtual function
        cout << "The area is " << area << endl;
        cout << "The perimeter is " << perim << endl;
    }
protected: // protected access specifier
    double area, perim;
};


#endif

circle.cpp：

#include "shape.h"
#include <iostream>
using namespace std;
class Circle : public Shape
{
public:
    void compute_area() { area = pi * radius; }
    void compute_perimeter() { perim = 2 * pi * radius; }
    void read_shape_data() {
        cout << "Enter radius of the rectangle : ";
        cin >> radius;
    }
private:
    int radius;
    double pi = 3.14159265359;
};

rectangle.cpp：

#include "shape.h"
#include <iostream>
using namespace std;
class Rectangle : public Shape
{
public:
    void compute_area() { area = width * height; }
    void compute_perimeter() { perim = 2 * width + 2 * height; }
    void read_shape_data() {
        cout << "Enter width of the rectangle : ";
        cin >> width;
        cout << "Enter height of the rectangle : ";
        cin >> height;
    }
private:
    int width, height;
};

RightTriangle.cpp：

#include "shape.h"
#include <iostream>
using namespace std;
class RightTriangle : public Shape
{
public:
    void compute_area() { area = base * height; }
    void compute_perimeter() { perim = pow((pow(base, 2) * pow(height, 2)), 2); }
    void read_shape_data() {
        cout << "Enter base length of triangle : ";
        cin >> base;
        cout << "Enter height of triangle : ";
        cin >> height;
        cout <<  
    }
private:
    int radius, base, height;
};

test.cpp（测试类）：

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

int main(){
    int choice;
    Shape* shape_ptr = NULL;
    cout << "Enter 1 for circle, 2 for rectangle, 3 for right angled triangle or 0 for exit";
    cin >> choice;
    switch (choice){
        case 1:
            shape_ptr = new Rectangle;
            break;
    }

    shape_ptr->read_shape_data();
    shape_ptr->compute_area();
    shape_ptr->compute_perimeter();
    shape_ptr->print_result();
    delete shape_ptr;

    return 0;
}

感谢您的时间，我很乐意回答您的任何问题。

Answer 1

“shape.h”标题不会自动了解sess.run()等派生类的定义，因此您的测试文件也需要包含这些标题：

Rectangle

看起来您在.cpp文件中定义了派生类。将这些声明移动到头文件中，然后在.cpp文件中定义它们。

虚函数和多态 - 无法在测试类中声明对象

1 个答案: