Question

My question is how to access and modify a 2D array defined in one class that is friends with another class. Below are some details on my question:

In class A I declare and allocate the appropriate space for my 2D array (pointer-to-pointer) u.

Class A
{
   public:
   friend class B;
   long double **u; 
   int fun;
   void make(); 
};
void A::make()
{
  long double **u = new long double *[nx];
  for (int i=0;i<nx;i++)
  u[i] = new long double [ny];
  int fun = 9;
}

Class A is friends with Class B; I need to use the array I declared in Class A in a function defined in class B. Below is my Class B:

class B
{
   public:
   void get(A*);
};

void B::get(A *pt)
{
   using namespace std;
   cout << pt->fun;
   cout << pt->u[0][0];
}

I get a Bus error on my second cout pt->u[0][0]. Is there a simple way to use this setup I have to access my u[][] array? I think that I get the error because the pointer points to the 1st entry of my array, thus my whole 2D array is saved in memory as a single row (thinking aloud here). I’m a Fortran guy so this stuff is a little new to me.

Any help or “pointers” to other helpful threads would be appreciated.

Thank you !

Alberto

Answer 1

I think you get error because A::u is not initialized ( in method A::make you initialize a local variable u, not member. You need to change

void A::make()
{
  long double **u = new long double *[nx]; // should be just u, or this->u.