🚀 go-pugleaf

Hi
While we (someone) work on your problem, have you been to
http://www.inquiry.com/techtips/cpp_pro/

there are lots of problems and answers


From Eric


New C Programmer <s_joanis@siebe-ene.com> wrote in message
news:88q96p$d3f$1@bob.news.rcn.net...
> I am trying to change the value of a pointer in a function. I successfully
> change it in the function but when I get back to the calling function it
> returns to the original value.
>
> This is the calling function from llist.cpp (a test harness)
>
>    if ( my_llist.i_traverse( from_where, data_ptr ))
>    {
>     element = data_ptr->storage;
>     cout << " Traversed node contained: " << element << ". ";
>    }else cout << "\nThere was an error, try again.\n";
>    break;
>
> This is the called function from llist.h.
>
> // *************************************************
> // traverse a list, if from_where = 1 then increment data_ptr by one node
> else return
> // list head in data_ptr.
> // *************************************************
> BOOLEAN llist::i_traverse ( BOOLEAN from_where, NODE *data_ptr )
> {
>  int pos = 0;
>  int count;
>  NODE *top_ptr = LinkedList;
>  NODE *temp_ptr = LinkedList;
> // NODE *temp_ptr2 = *data_ptr;
>
>
>  count = llist::i_size();
>  if ( count <= 0 )
>  {
>   return ( FALSE ); /* position out of range */
>  }
>
>  if (data_ptr == NULL)
>  {
>   data_ptr = LinkedList;
>   return ( TRUE );
>  }
>
>  if ( from_where == 0 )
>  {
>   data_ptr = LinkedList;
>   return ( TRUE );
>  }
>
>
>  if ( data_ptr->next != NULL )
>  {
>   data_ptr = temp_ptr->next;
>   return ( TRUE );
>  }
>  else
>  {
>   return ( FALSE );
>  }
> }
>
> Thanks,
>
> Steve
>
>

Hello,

A pointer is a variable just like the others, exept it is made
to hold an adress to an object, hence if you want to modify it
in a function, you should pass it by reference to allow 
modifications.

Simply change your prototype :

  BOOLEAN llist::i_traverse ( BOOLEAN from_where, NODE *data_ptr )
to
  BOOLEAN llist::i_traverse ( BOOLEAN from_where, NODE * & data_ptr )

//                                                      ^^^
// Note the '&' 
//

Regards, Laurent.

New C Programmer wrote:
> 
> I am trying to change the value of a pointer in a function. I successfully
> change it in the function but when I get back to the calling function it
> returns to the original value.
> 
> This is the calling function from llist.cpp (a test harness)
> 
>    if ( my_llist.i_traverse( from_where, data_ptr ))
>    {
>     element = data_ptr->storage;
>     cout << " Traversed node contained: " << element << ". ";
>    }else cout << "\nThere was an error, try again.\n";
>    break;
> 
> This is the called function from llist.h.
> 
> // *************************************************
> // traverse a list, if from_where = 1 then increment data_ptr by one node
> else return
> // list head in data_ptr.
> // *************************************************
> BOOLEAN llist::i_traverse ( BOOLEAN from_where, NODE *data_ptr )
> {
>  int pos = 0;
>  int count;
>  NODE *top_ptr = LinkedList;
>  NODE *temp_ptr = LinkedList;
> // NODE *temp_ptr2 = *data_ptr;
> 
>  count = llist::i_size();
>  if ( count <= 0 )
>  {
>   return ( FALSE ); /* position out of range */
>  }
> 
>  if (data_ptr == NULL)
>  {
>   data_ptr = LinkedList;
>   return ( TRUE );
>  }
> 
>  if ( from_where == 0 )
>  {
>   data_ptr = LinkedList;
>   return ( TRUE );
>  }
> 
>  if ( data_ptr->next != NULL )
>  {
>   data_ptr = temp_ptr->next;
>   return ( TRUE );
>  }
>  else
>  {
>   return ( FALSE );
>  }
> }
> 
> Thanks,
> 
> Steve