static problem

asnowman

class point3d {
public:
      float x () {return _x;
private:
    static float _x;
};

main ()
{
    point3d rout;
    point3d * pt =&rout;
    cout << rout.x () << endl << pt-> x () << endl;
}

In the above program, an error LNK2001: unresolved external symbol "private: static float Point3d :: _ x" (? _X @ Point3d @@ 0MA) is always reported as an error. I can remove the static and it can run, please prawn instructions!

julines

STATIC member variables are placed outside the object and need to be defined
class point3d {
public:
      float x () {return _x;
private:
    static float _x;
};

float point3d :: _ x;
main ()
{
    point3d rout;
    point3d * pt =&rout;
    cout << rout.x () << endl << pt-> x () << endl;
}

zhilong821

All static data is placed in the static area, it does not belong to any one object alone

But only the class in which it is declared can access it (in the private case), and it can only be defined once