default constructor Line class

[vxk]

I have a Line class and a FRIEND Point class in it .The default constructor of the point class takes 2 int arguements that is x-location and y-location .

eg. Point p(10,3);

I am trying to make the default constructor for the line class which satisfies the point slope form of the Line that is the constructor for the Line class takes 2 arguements one of the type Point and the other of the form double(for slope).


But I am finding that all of the below code is working .....is it all correct ?

// default constructor 
Line(Point = 0,double  = 0); 
Line(Point = (0,0),double = 0);
Line(Point = (0,0,0), double = 0);  //?

Thanks !

[MiiNiPaa]

Does Point have constructor takinf one argument? Because this is what you call in all cases.

[vxk]

yeah copy constructor ....

[MiiNiPaa]

No, of type int. Maybe several arguments with some default values?

Point = (0,0,0) is equivalent to Point = 0. Only way for this to work is to have Point(int) constructor.

[dhayden]

You should pass the Point by const reference to avoid having to copy it. That complicates the constructor but there's a way to deal with it:

class Line {
public:
    Line (const Point &p = dummy, double slope =0);
private:
    static Point dummy;
};

The default argument for p is a private static member of the class called dummy. You have to define this is the file that implements the class.

[vxk]

class Point
{ public:
    Point(double=0.0,double=0.0);    // default constructor
    Point(const Point&);             // copy constructor
    ~Point();                        // destructor
    Point& operator=(const Point&);  // assignment operator
    double x() const;
    double y() const;
    string toString() const;
  private:
    double _x, _y;
};

[MiiNiPaa]

(0,0,0) is equals to 0
(0, 0) is also equals to 0
Read info on , operator
So both (0, 0) and (0, 0, 0) calls your "default" constructor with second parameter taking default value.

As there is no sense to convert integer (or double) I suggest to make default constructor explicit.