virtual float z(){return 0.0;}
private:
float _x, _y;
};
3虚继承下
class point3d：public virtual point
{
public：
point3d ( float x = 0.0, float y=0.0, float z =0.0)：point (x,y),_z(z){}
point3d( const poin3d& rhs)：point(rhs),_z(rhs.z){}
~point3d();
point3d & operator = (const point3d &);
virtual float z() {return _z;}
protected:
float _z;
};
下面就是point3d的构造函数被扩充的内容
point3d *point3d：：point3d( piont3d *this ,bool _most_derived,float x, float y, float z)
{
