Question

Very simple question – how can I access data for a struct that lives inside the heap?

Additional information:: I have a class called “A” and a struct within this class called “B”. Every “B” that is created will live on the heap. Class “A” is intended to have a vector of “B”‘s as a private data member (ie. the class “A” can hold many “B”‘s). I have a method in class “A” that will add another new instance of “B” in the vector that “A” has. I also have another method in class “A” that will update every single element that is in the vector of “B” instances. My questions are:

How do I use the getters and setters within my struct?

Here is some code that might help (note: grafix.h is a graphical library)

//.h file
#pragma once
#include <vector>
#include "grafix.h"

class A
{
    public:
        ~A();
        A();

        void addB();
        void updateB();

    private:

        struct B
        {
                 public:
                     ~B()
                     {
                           delete p_b;
                     p_b = 0;
                     }

                     B()
                     {
                     p_b = new B; //I need this here

                     p_ball->x = 0;
                     p_ball->y = 0;
                     p_ball->r = 15;

                      }
                      void setxy(int X, int Y) 
                      {
                     //What does this look like?
                                       //This?
                                       x = X; //?
                                       y = Y;
                      }

                      int retx()
                      {
                                        //Likewise.... ?
                      return x; //?
                      }


                      int rety()
                                  {
                                         return y;
                                  }

                       void update()
                       {
                          draw();

                                           //Movement code taken out for time being
                       }

                  private:
                       int x,y; //xy
                       int r; //radius


                       B* p_b; //pointer to object, do I need this?

                       void draw()
                       {
                         draw_circle_filled(x,y,r); 
                                          //how can I access the data within the struct B here?
                                          //do I use the getters/setters? dereference??
                       }

          };

vector <Ball*> bs; //Holds all of the B's that have been created

};

And then the .cpp file that has the methods. This is where I have my question, am I typing in the right syntax??

#include "A.h"

A::A()
{
        addB();
}

void A::addB()
{
      B* b;

      bs.push_back(b);
}

void A::updateB()
{
       for(int i = 0; i < bs.size(); i++)
       {
            bs[i]->update();
       }
}

Answer 1

this is criminal :

void A::addB()
{
      B* b;

      bs.push_back(b);
}

B* b is NOT initialized.
Having a reference on it in you container is criminal: dereferencing this address doesnt make sense and is undefined behaviour / crash.

you should assign this way:

{
      B* b = new B;

      bs.push_back(b);
}

Edit: as Kevin commented below as is there is still a memory leak. You’d rather use a container of std::shared_ptr<B>. This way the B oject will be deleted when nobody keeps a shared_ptr pointing to it.