Prototype

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#include<iostream>

using namespace std;
// prototype
class Img {
public:
    static void FindAndClone() {
        for (int id = 0; id <= count; ++id) {
            _Prototypes[id]->clone()->print();
        }
    }
    // why vrtual
    virtual Img* clone() const = 0;
    virtual void print() const = 0;
    // why not virtual
    void addPrototype(Img* obj) {
        Img::_Prototypes[count++] = obj;
    }
private:
//declaration
    //why static
    static Img * _Prototypes[10];
    static int count;
};
//defination
Img* Img::_Prototypes[10];
int Img::count = 0;

class SpotImg : public Img{
public:
    virtual void print() const {
        cout << "add class SpotImg" << endl;
    }
protected:
    virtual Img* clone() const{
        return new SpotImg(1);
    }
    
    SpotImg(int dummy) {}
private:
    //why static
    static SpotImg _SpotImg;
    SpotImg() {
        addPrototype(this);
    }
};

 SpotImg SpotImg::_SpotImg;

class LandSatImg : public Img{
public:
    virtual void print() const {
        cout << "add class LandSatImg" << endl;
    }
protected:
    virtual Img* clone() const{
        return new LandSatImg(1);
    }
    
    LandSatImg(int dummy) {}
private:
    static LandSatImg _LandSatImg;
    LandSatImg() {
        addPrototype(this);
    }
};

LandSatImg LandSatImg::_LandSatImg;

int main() {
   Img::FindAndClone();
    return 0;
}