c++ - 如何制作一个实例化类并将它们排序在地址列表中的循环？

Question

考虑 2 个变量(多边形的数量及其坐标):

int numberPoly= 2;
float polycoord[18]= {0,50,0,0,0,0,50,0,0,0,50,0,50,50,0,50,0,0};

，模型类(旨在将多边形类存储到列表中):

class model{
    public:
        model();
        void affect(int id, int address){
            polyclasses[id]=address;
        }
    private:
        string name;
        vector<int> polyclasses;
};

，一个多边形类(我必须在模型的多类列表中排序):

class polygone {
    public:
        polygone();
        void affect(int id, int coord){
            ABC[id]=coord;
        }
    private:
        int id;
        float ABC[9]={0.0};
};

我想编写一个函数(参见“builder”)来实例化 n 个 Polygon 类并在数组(Model 类中的“polyclasses”)中对它们进行排序(使用它们的内存地址，如 id)。所以，我没有到达。这是我的一些未完成的构建器函数:

void builder(){
    int from = 0; int subfrom = 0;
    for(int i=0; i < numberPoly - 1; i++){
        from = 0; subfrom = 0;
        polygone poly();
        !!! need to put that instance in Model's polygon list !!!
        ...
        for(int j=from; j < (polycoord.size())-1; j++){
            poly.affect(subfrom, polycoord[j]) ...
            subfrom++;
        }
        from += 3;
    }
}

这是我的第一个 C++ 项目。我正在编写一个轻型 2d 引擎。

Answer 1

您需要在 vector 中存储实例指针，并使用 new 关键字分配对象。在您的模型析构函数中，您需要删除该对象以避免内存泄漏。

// Model.h
// Class name should begin with uppercase by convention
class Model{
    public:
        Model();
        ~Model();
        void builder(); 
        // Implementation should go in cpp file
        void affect(int id, int address);
    private:
        // Having a m_ prefix on private variable is useful to make your code more readable so a reader can easily know if a variable is private or not
        string m_name;
        vector<Polygon*> m_polyclasses;
};

// Polygone.h
class Polygone {
public:
    Polygone();
    // Don't forget destructor
    ~Polygone();
    // Implementation should go in cpp file
    void affect(int id, int address);
private:
    int m_id;
    // Use std::array in C++ and give meaningful name to your variable
    // float m_ABC[9]={0.0}; is replaced by :
    std::array<float, 9> m_coordinates;
};

// Model.cpp  
void Model::builder() {
    int from = 0; int subfrom = 0;
    for(int i=0; i < numberPoly - 1; i++){
        from = 0; subfrom = 0;
        Polygone * poly = new Polygone();
        // A pointer of poly is now stored in Model
        this->polyclasses.push_back(poly);
        // Your polygone object should initialized in the constructor or in a member function of the class Polygone.
        for(int j=from; j < (polycoord.size())-1; j++){
            poly->affect(subfrom, polycoord[j]) ...
            subfrom++;
        }
        from += 3;
    }
}

Model::~Model() {
    for(auto p: this->polyclasses) {
        // Avoid memory leak
        delete p; 
    }
    this->polyclasses.clear();
}

您还可以存储 std::unique_ptr而不是一个普通的指针。在这种情况下，您不需要delete。