doubt not going on : operator

[Mack]

Hi I have the following code:

struct Point
{
    double x, y;
 
    inline Point(double X = 0, double Y = 0) : x(X), y(Y){ }       
};
 
can anybody clue WHY after " ) " , the programmer has used  : and in braces { } no code is wriiten.
does he mean to make abstract class . or abstract structure?
Consequently he has taken this example carried forward to make segment class using Point studture where he makes use of
 
class Segment
{
public:
    inline Segment(const Point &a, const Point &b) : pointA(a), pointB(b){ }
 
         inline void setPointX(const Point &val) {pointA = val;}
    inline void setPointY(const Point &val) {pointB = val;}
 
Private :
Point pointA, point B
}
 

May i seek anybody help please.

Thanks and Regards,
Mack.

[horace1]

the : x(X), y(Y) in

struct Point
{
    double x, y;
 
    inline Point(double X = 0, double Y = 0) : x(X), y(Y){ }       
};
 

is an initialisation list to initialise the data member x and y, have a look at the tutorial
http://www.cprogramming.com/tutorial/initialization-lists-c++.html

in addition to other reasons it is more efficient than to use assignment, e.g.

  inline Point(double X = 0, double Y = 0) 
       { x=X; y=Y; }