Weird numbers in C++ array of objects - c++

Question

I've been trying to make an class with an array of objects created dynamically. I overloaded the operator + to add (only this for now) a new object to a group of objects (class to class). THe problem is when I read the data in the array, I get all sorts of big numbers . Here is the code:
#include<iostream.h>
class Figura {
public:
int x, y, poz;
int tip; //1 = punct ; 2 = dreapta; 3 = dreptunghi
Figura() { };
Figura(const Figura&) { };
};
class Grup {
private:
int nr_elemente;
Figura *figuri;
public:
int i;
Grup(int nr_el) {
nr_elemente = nr_el;
figuri = new Figura[nr_elemente];
i = 1;
}
~Grup() {};
Grup(const Grup&) {};
int _nr_elemente() {
return i;
}
void adauga_element(Figura fig) {
if( i <= nr_elemente)
figuri[i++] = fig;
else
cout<<"Grupul a atins numarul maxim de figuri.";
}
void afiseaza_elemente() {
for(int j = 1; j <= i; j++)
cout<<"Figura nr : "<<j<<"tip: "<<figuri[j].tip<<figuri[j].x<<" "<<figuri[j].y<<" "<<figuri[j].poz;
}
friend Grup operator+(const Figura& fig1, const Figura& fig2) {
return fig1.poz + fig2.poz;
};
friend Grup operator+(const Grup& gr1, const Grup& gr2) {};
void operator+(const Figura& fig);
friend Grup operator*(const Grup& fig) {};
};
void Grup::operator+(const Figura& fig) {
Grup::adauga_element(fig);
}
class Punct : public Figura
{
public:
Punct(int poz) {
Punct::tip = 1;
Punct::poz = poz;
}
};
class Segment : public Figura
{
public:
Segment(int poz, int x) {
Segment::tip = 2;
Segment::poz = poz;
Segment::x = x;
}
};
class Dreptunghi : public Figura
{
public:
Dreptunghi(int poz, int x, int y) {
Dreptunghi::tip = 3;
Dreptunghi::poz = poz;
Dreptunghi::x = x;
Dreptunghi::y = y;
}
};
void main(void) {
Grup gr(1);
Punct pct(1);
Segment sgm(3, 5);
gr + pct;
gr + sgm;
//cout<<gr.i;
cout<<sgm.x;
gr.afiseaza_elemente();
}

Answer 1

Array indexes run from 0 to N - 1, when N is the array size. The following code will result in out of bounds array access:
void adauga_element(Figura fig) {
if( i <= nr_elemente)
figuri[i++] = fig;
else
cout<<"Grupul a atins numarul maxim de figuri.";
}
Change to:
if( i < nr_elemente)
Same problem in afiseaza_elemente().
As you have dynamically allocated members a destructor must delete[] the dynamically allocated array and a copy constructor and assignment operator need to be correctly implemented, or declared private to prevent copying. As this is C++, consider using std::vector<Figura> instead of an array.

Answer 2

A more simple example would improve understanding.
In any case, your problem is known as object slicing.
In short, you cannot put a derived object in an array of base objects.
To solve the problem you can change the figuri data member to be an array of pointers to Figura:
Figura ** figuri;
// ...
figuri = new Figura*[nr_elemente];

Answer 3

You're not initializing any members. You should do that in the constructor.
For example:
Punct pct(1);
only initializes the members tip and pos, but x and y will contain garbage values, which you probably end up seeing.
You also shouldn't be using a dynamically allocated array as a member - Figura *figuri; but a std::vector. This would save you also from the undefined behavior you're encountering when adding new figures.
Also, note that your destructors and copy constructors have no implementation, which is a source for bugs.
void adauga_element(Figura fig)
passes the object fig is passed by value, so a copy constructor should be implemented.