Re: Passing values to functions

[Dino Cherian K <inimss yahoo com>]

Hi

I didn't actually get the actual use of such an argument (the gpointer
data). Would you please explain a bit in detail, with a typical
use/application.

Thanks
Dino

zze-coframi balr001 wrote:
> 
> Hello,
> 
> you have to cast your data before sending them.
> For example, if you want to pass a char *, in your callbacks, you can use
> data as a char *.
> 
> char * toto = "My data";
> gtk_signal_connect (GTK_OBJECT (button), "pressed",
> GTK_SIGNAL_FUNC(callback), (char *) toto);
> 
> void callback (GtkButton * button, gpointer data){
>         printf ("%d\n", (char *) data);
> }
> 
> You can pass all kind of pointer you want (GtkWidget *, char *, int * .....)
> , you just have to cast them before using them.
> 
> Isabelle
> 
> -----Message d'origine-----
> De : Dino Cherian K [mailto:inimss yahoo com]
> Envoye : dimanche 20 janvier 2002 07:32
> A : Sven Neumann
> Cc : Shiraz Baig; gtk-list gnome org
> Objet : Re: Passing values to functions
> 
> Hi
> 
> Seeing this discussion I have a doubt.
> 
> What does this gpointer data in the function arguments mean.
> How I can use it and in what all contexts.
> >   void callback (GtkButton *button,
> >                  gpointer   data);
> 
> Thanks
> Dino
> 
> Sven Neumann wrote:
> >
> > Hi,
> >
> > Shiraz Baig <shiraz_baig yahoo com> writes:
> >
> > > I am a newbie. Can anyone tell me, in the following
> > > elementary program, why doesn't the function "hello"
> > > that it has not been passed any data. Because in
> > > gtk-signal-connect, we are passing NULL data.
> > > Wherefrom is this data coming. In another case, I have
> > > seen drawing_area being passed like this. How does it
> > > get to the function "hello".
> >
> > what was the question again? The code you posted looks
> > OK and I can't see what your question is. data as passed
> > to the function hello should indeed be NULL.
> >
> > If you have seen a drawing_area pointer in a signal
> > callback where you expected your user_data you most
> > probably connected a callback with a wrong signature.
> > Not all signals are declared as the clicked signal
> > of a GtkButton:
> >
> >   void (* clicked)  (GtkButton *button);
> >
> > which expects a callback of the form
> >
> >   void callback (GtkButton *button,
> >                  gpointer   data);
> >
> > The signal "expose_event" of a GtkWidget for
> > example is defined as
> >
> >   gint (* expose_event) (GtkWidget       *widget,
> >                          GdkEventExpose  *event);
> >
> > so you need to use a callback of the form
> >
> >   gint callback (GtkWidget       *widget,
> >                  GdkEventExpose  *event,
> >                  gpointer         data);
> >
> > Or you'd get the event pointer instead of the expected
> > user_data.
> >
> > Salut, Sven
> > _______________________________________________
> > gtk-list mailing list
> > gtk-list gnome org
> > http://mail.gnome.org/mailman/listinfo/gtk-list
> 
> _________________________________________________________
> Do You Yahoo!?
> Get your free @yahoo.com address at http://mail.yahoo.com
> 
> _______________________________________________
> gtk-list mailing list
> gtk-list gnome org
> http://mail.gnome.org/mailman/listinfo/gtk-list

_________________________________________________________
Do You Yahoo!?
Get your free @yahoo.com address at http://mail.yahoo.com