关于指针和对象的问题

Question

我的最后一个问题是一团糟.我收到了错误的输出.

所以在这里我有我的主要内容:

image = QImage(width, height, 32); // 32 Bit
Color amb(0.1,0.1,0.1);
Color difCoef(0.75,0.6,0.22);
Color spec(0.5,0.5,0.5);
double shineExp = 3.0;
Sphere *s = new Sphere(Point(0.0,0.0,-5), 100.0, amb, difCoef, spec, shineExp);
shapes.push_back(s);

其中shape是vector <Shape*>形状;

Shape *x = shapes[0];
cout << "Shine" << x->shine << endl;

即使答案应为3.0,也打印出零.

以下是我的课程:

#include "shape.h"
class Sphere : public Shape
{
    public:
    Point centerPt;
    double radius;
    Color ambient;
    Color dif;
    Color spec;
    double shine;

    Sphere(Point center, double rad, Color amb, Color difCoef, Color specu, double shineVal)
    {
        centerPt = center;
        radius = rad;
        ambient = amb;
        dif = difCoef;
        spec = specu;
        shine = shineVal;
    }

---

class Shape
{
    public: 
    Shape() {}
    ~Shape(){} 
    Color ambient;
    Color dif;
    Color spec;
    double shine;
    virtual bool checkIntersect(Point p, Point d, Point &temp) = 0; // If intersects, return true else false.
    virtual Point getNormal(Point intPt) = 0; // Get the normal at the point of intersection
    //virtual void printstuff() = 0;

};

Answer 1

问题是你在派生类中重复你的变量声明.你不需要重新声明变量一样double shine,它们已经在Shape,在派生类中Sphere.由于Sphere继承自Shape,所有公共成员变量都会Shape自动继承Sphere,并且不需要重新声明.重新定义它们将导致两个不同的成员变量,即Sphere::shine完全不同的变量Shape::shine.

因此,当您为一个值分配一个值Sphere::shine,然后使用Sphere基类Shape指针访问一个实例时,其值shine将不会是您所期望的.