OCILib - visibility of variables

Question

I'm passing variable cn to function myconnect by pointer. While stepping in the debugger the cn is correct inside of myconnect(). But no more in main(). Can't I do this like that (see code below)? When I do the initialization and connection in main, it works. And I can pass cn to other functions. But I would prefer to exclude it from there(main) and have in separate function.

int myconnect(OCI_Connection* cn  )
{
  if (!OCI_Initialize(err_handler, NULL, OCI_ENV_DEFAULT))
  return 0;
  cn = OCI_ConnectionCreate( DB, DBUSER, DBPASS, OCI_SESSION_DEFAULT);
  if (cn == NULL) return 0;

  return 1;
}

int main()
{
  OCI_Connection* cn;

  if (myconnect(cn) == 0)
  {
    dbErr =1;
  }
}

Answer 1

The variable cn is passed by value to the function myconnect, i.e. the function receives a copy and assign a value to that copy. This has no effect in main.

To have a effect, you have to passed it by reference. In C, that means you have to pass a pointer to the variable, which is itself a pointer:

int myconnect(OCI_Connection** cn)
{
  if (!OCI_Initialize(err_handler, NULL, OCI_ENV_DEFAULT))
      return 0;
  *cn = OCI_ConnectionCreate(DB, DBUSER, DBPASS, OCI_SESSION_DEFAULT);
  if (*cn == NULL)
      return 0;

  return 1;
}

int main()
{
  OCI_Connection* cn;

  if (myconnect(&cn) == 0)
  {
    dbErr =1;
  }
}