Question

I’m working on an opengl project and I got a problem with some of my classes:

There are 3 main classes:

---

class scene{
public:
   scene();
   object** elements;
   unsigned int nb_elements;

   void add_object(object* _element){
       objet** p_elements=elements;

       while(p_elements-elements!=nb_elements)
           p_elements++;

      *p_elements=_element;                    //here is the bug
      nb_elements++;
    }


}
[...]
};

---

class object{
public:
    object();
    [...]
};

---

class point : public object{
point();
point(double _x, double _y, double _z,double _r);
[...]
}

---

I initialize the scene after initializing Opengl, in the same function:

void GLWidget::initializeGL(){

   [OpenGL initialization]

   _scene=new scene;
   point* s1=new point(0.0,0.0,3.0,1.0);
   _scene->add_object(s1);

}

The bug is in the scene::add_object function. I don’t understand why it doesn’t work since *p_elements and _element are both pointers. I gues it’s a cast problem but I don’t know how to fix it. I tried dynamic cast: the bug remains.

Thank you for your help,

Kamouth

Answer 1

objet** p_elements=elements; sets p_elements to uninitialized memory. So p_elements-elements!=nb_elements, p_elements++; and *p_elements=_element; invoke undefined behavior. I’m not going to advise you to initialize the memory, but merely to use std::vector and smart pointers instead.

The double pointers suggest you come from a C background, but if you want to do C++ development you have to learn C++ idioms. Don’t stick to writing C code in C++.