C'est ceci que tu veux ?

int kernel__hd2full(HANDLE h, char buffer[18])
{
  const char *name = kernel__Hd2Sym(h);
  if (name == NULL)
    return -1;
  HANDLE h_folder = kernel__Ptr2Hd(name);
  if (h_folder < 0)
    return -2;
  const char *folder = kernel__Hd2Sym(h_folder);
  if (folder == NULL)
    return -3;
  sprintf (buffer, "%s\%s", folder, name);
  return 0;
}