Re: Passing values to functions

[Dino Cherian K <inimss yahoo com>]

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
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