inheritance

[Winsu]

I am having troubles to make the constructors of my derived class, I believe that I should call twice the constructor to create a Sline object, but I should call the cosntructor twice referenced to p1 and p2( supossing that It's the solution) I can't imagine how to do it...Thanks!!

  #include <stdio.h>
#include <iostream>

class point{
	protected:
		int x,y,z;
	public:
		
		point():x(0),y(0),z(0){};
		
		point(int a,int b,int c):x(a),y(b),z(c){};
};

class Sline: public point{
	protected:
		point p1,p2;
		
	public:
		Sline():p1.x(0),p1.y(0),p1.z(0),p2.x(0),p2.y(0),p2.z(0){};
		Sline(point a,point b):p1.x(a.x),p1.y(b.x),p1.z(c.x),p2.x(b.x),p2.y(b.y),p2.z(b.z){};
		
		
		
};

[AbstractionAnon]

First off, Sline should not inherit from point. Sline is NOT a point. Sline HAS two points.

Line 19: you don't need to initialize each x,y,z to zero. point's default constructor already does that.

   Sline()
   {}

In fact this constructor isn't really needed, since the compiler will provide a default constructor automatically.

Line 20 can be written more concisely by using point's implicit copy constructor:

  Sline (point a, point b) : p1(a), p2(b)
  {}

[Winsu]

Their relation should me more friendship than inheritance, arent they=

[MiiNiPaa]

It should be composition, actually.

[Winsu]

A composition is just a system class where some classes have objects of other classes,isnt it?

[MiiNiPaa]

Yes. Your Sline have two Points. That it. It is not a Point itself.

[andywestken]

Edit: reading back up the thread I see I am restating what AbstractionAnon has already said...

But you do need to provide a default constructor if you declare other sorts of constructors (e.g. point(int a,int b,int c) stops the automatic generation of the default constructor, but not the copy constructor.) So need either:

class point {
    private:
        int x,y,z;
    public:
        point():x(0),y(0),z(0){};
        point(int a,int b,int c):x(a),y(b),z(c){};
};

or

class point {
    private:
        int x,y,z;
    public:
        point() = default; // for C++11
        point(int a,int b,int c):x(a),y(b),z(c){};
};

A composition is just a system class where some classes have objects of other classes,isnt it?

A composite (or composite class) is one which has members which are classes. That is, it is composed of other classes.

Not sure what you mean by "system class"?

Andy

class point {
    private: // why was it protected?
        int x,y,z;
    public:
        point():x(0),y(0),z(0){};
        point(int a,int b,int c):x(a),y(b),z(c){};
        // could add copy constructor, but not needed...
        //point(const point& p):x(p.x),y(p.y),z(p.z){};
};

class Sline { // no longer incorrectly inherits from point
    protected:
        point p1,p2;
        
    public:
        Sline() {}; // point constructors already init point members
        Sline(point a,point b):p1(a), p2(b){}; // now using point copy constructor
};

int main()
{
    point p1(1, 2, 3);
    point p2(4, 5, 6);

    point p3;
    point p4(7, 8, 9);

    Sline s1(p1, p2);
    Sline s2(p3, p4);
    Sline s3;

    return 0;
}

[Winsu]

I meant with system class a set of class....thanks!!