C++朋友构造

Question

我有两个类：Point，即只生活在Space

class Point 
{ 
private: 
    Point(const Space &space, int x=0, int y=0, int z=0); 
    int x, y, z; 
    const Space & m_space; 
}; 

构造函数是故意私人的，我不希望它被直接调用。 我想创建这样的点

Space mySpace; 
Point myPoint = mySpace.Point(5,7,3); 

有没有什么办法可以这样做？谢谢。

Answer 1

是的，声明Space::Point()作为朋友的方法。该方法将获得访问Point的私人会员。

class Point 
{ 
public: 
    friend Point Space::Point(int, int, int); 
private: 
    // ... 

Answer 2

我会做这样的：

class Space 
{ 
public: 
    class Point 
    { 
    private: 
     Point(const Space &space, int x=0, int y=0, int z=0); 
     int m_x, m_y, m_z; 
     const Space & m_space; 

    friend class Space; 
    }; 

    Point MakePoint(int x=0, int y=0, int z=0); 
}; 

Space::Point::Point(const Space &space, int x, int y, int z) 
    : m_space(space), m_x(x), m_y(y), m_z(z) 
{ 
} 

Space::Point Space::MakePoint(int x, int y, int z) 
{ 
    return Point(*this, x, y, z); 
} 

Space mySpace; 
Space::Point myPoint = mySpace.MakePoint(5,7,3);