Re: Glib -> GList

[Norm Reitzel <NormReitzel swbell net>]

Metnetsky:

It's easier than it seems.  Suppose you have defined a structure to hold some data about a patient.  This structure might contain stuff about his diseases, his white count, his last treatment date, etc.

   struct patient {  int     count;            // white count
                     time_t  last_treated;     //   date last treated
                     char    *complaint;       //   whassamatta
                  };

You would allocate one of these structures and fill it in with data ( though I would use a class, and fill it in in the constructor ).

   struct patient  *sick_guy;

   sick_guy = new struct patient;
   
   sick_guy->count = his_white_count();   //  fill in the data, etc.

THen you could insert this structure into a Glist as so:

	GList  *list_of_patients  =  new GList;

        list_of_patients->data = (void *) sick_guy;

Later on, if you wanted to refer to this item, you would use a reverse cast to assign the void pointer from data to a typed pointer, like so:

        sick_guy = ( struct patient * ) ( list_of_patients->data );

The whole purpose of a void pointer is that it is untyped, and hence can hold whatever kind of data you want it to point to.

You should read the sections of K&R on pointers carefully, as C manages pointers quite well, but it LEAVES THE MANAGMENT OF THE DATA entirely to YOU, the programmer.  Part of the reason for C++ and its classes, and Java, is that many people have a lot of difficulty managing data objects via pointers.

Don't know if that helps or not.

-- Norm Reitzel


> I was wondering if you, or anyone else could explain how to use the data void 
> pointer in GList to point to another structure.  Any kind of structure would 
> do, the simpler the better I'd imagine.  Thanks in advance, and I hope this 
> isn't something too complicated to email.  Oh, if you know of a site that has 
> this in some tutorial/example/documentation form that would be perfect too.
> 
> ~ Metnetsky