C++ inheritance how to get variables values - c++

Question

I'm trying to create a small program for a lessons.
But In My class that herit , I don't have values of the superclass.
, here's the code
Point.h
#ifndef Point_H
#define Point_H
#include <iostream>
class Point{
public:
Point();
void set_values (int a, int b);
void set_values (int a, int b, int c);
void affichervaleurs();
protected:
int x ;
int y ;
int z ;
};
#endif
Point.cpp
#include <iostream>
#include "Point.h"
using namespace std;
Point::Point(){
x=0;
y=0;
z=0;
};
void Point::set_values (int a, int b){
x=a;
y=b;
}
void Point::set_values (int a = 0, int b = 0, int c = 0){
x=a;
y=b;
z=c;
}
void Point::affichervaleurs(){
cout << "X = " << x << endl;
cout << "Y = " << y << endl;
}
Carre.h
#ifndef Carre_H
#define Carre_H
#include "Point.h"
class Carre:public Point{
public:
int Aire (){
};
void affichercar(){
};
};
#endif
Carre.cpp
#include <iostream>
using namespace std;
#include "Point.h"
class Carre:public Point{
public:
//Carre::Carre(int a, int b);
int Aire (){
return (x * y);
}
void affichercar(){
cout << "Coordonnees X:" << x << endl;
}
};
main.cpp
#include <cstdlib>
#include <iostream>
#include "Carre.h"
#include "Point.h"
using namespace std;
int main()
{
Point MonPoint ;
cout << "Default values:" << endl;
MonPoint.affichervaleurs();
MonPoint.set_values(4,6);
cout << "Setting values:" << endl;
MonPoint.affichervaleurs();
Carre MonCarre;
MonCarre.set_values(4,6,0);
MonCarre.set_values(5,8);
MonCarre.affichercar();
cout << MonCarre.Aire() << endl;
system("PAUSE");
return EXIT_SUCCESS;
}
The problem is, when I call this line :
cout << MonCarre.Aire() << endl;
it returns a strange number. I'm sure that the problem is here :
int Aire (){
return (x * y);
};
Like the x and y are not linked with the superclass.
Can someone help me how to access my x and y values from my superclass in my class Carre ?
Other strange thing this line doesn't appear :
MonCarre.affichercar();
Thanks

Answer 1

You define the functions Aire and affichercar in Carre.h, but you need to declare them only if you want to write an implementation in Carre.cpp.
Edit: and your Carre.cpp is also wrong. You just need to rewrite Carre.* files.
Edit2. Let me do some code review and give you a working version of your code - just summarizing what was discussed in comments and my own thoughts.
Point.h
void set_values (int a, int b);
void set_values (int a, int b, int c);
If you want to define the default values of the arguments of the second function, you should do it in its declaration as was suggested in comments to your question. So it will be
void set_values (int a, int b);
void set_values (int a = 0, int b = 0, int c = 0);
But in this case it's not clear what function should be called if you write, for example, set_values(1, 2), therefore your code won't compile because of ambiguity (as also was mentioned in the comments). So you just have to keep only one extended version of this function with the default arguments. The Point.h will be in this case:
#ifndef Point_H
#define Point_H
#include <iostream>
class Point{
public:
Point();
void set_values (int a = 0, int b = 0, int c = 0);
void affichervaleurs();
protected:
int x ;
int y ;
int z ;
};
#endif
The Point.cpp is also changed a little bit:
#include <iostream>
#include "Point.h"
using namespace std;
Point::Point()
// it's better to initialize these variables here
// : x(0), y(0), z(0)
{
x=0;
y=0;
z=0;
}
void Point::set_values (int a, int b, int c){
x=a;
y=b;
z=c;
}
void Point::affichervaleurs(){
cout << "X = " << x << endl;
cout << "Y = " << y << endl;
}
Now let's consider the Carre.h file
class Carre:public Point{
public:
// IT'S DEFINITION WHICH IS USED WHEN YOU CALL THE FUNCTION
int Aire (){};
// IT'S DEFINITION WHICH IS USED WHEN YOU CALL THE FUNCTION
void affichercar(){};
};
Now I'm starting answering your questions:
The problem is, when I call this line :
cout << MonCarre.Aire() << endl;
it returns a strange number.
Yes, it's a strange number returned by the function defined in the Carre.h (not Carre.cpp) file.
I'm sure that the problem is here :
int Aire (){
return (x * y);
};
No, as you see, it's not.
Like the x and y are not linked with the superclass.
In fact they are.
Can someone help me how to access my x and y values from my superclass in my class Carre ?
You already have this access. It's okay to use protected members from base class in derived class in case of public inheritance.
Other strange thing this line doesn't appear : MonCarre.affichercar();
You mean it does nothing? But it's in perfect consistency with how you implement (define) the function in Carre.h (not Carre.cpp) file.
So let me change the code to make it work.
Carre.h
#ifndef Carre_H
#define Carre_H
#include "Point.h"
class Carre:public Point{
public:
int Aire (); // now it's declaration
void affichercar(); // now it's declaration
};
#endif
Carre.cpp
#include <iostream>
using namespace std;
int Carre::Aire (){
return (x * y);
}
void Carre::affichercar(){
cout << "Coordonnees X:" << x << endl;
}
I didn't compile this for myself, but the whole idea should be clear.

Answer 2

access my x and y values
From within Carre, you simply access them by 'x' and 'y'.
From outside, you cannot as they are not public.