what's the best way to handle variables and objects?

[Andreas Kotowicz <kotoml mynetix de>]

I'm looking for a clean solution on passing variables and objects from
gtk calls to callback functions and back.

I call for instance

g_signal_connect(G_OBJECT(button), "clicked",
G_CALLBACK(clear_timer_cb), progressbar);

and pass with it the object I'm working with. (progressbar has been
definded before: GtkWidget *progressbar = gtk_progress_bar_new(); )

now in clear_timer_cb I can modify the object:

void clear_timer_cb(GtkObject *window, void *data)
{
  GtkWidget *progressbar = data;
  gtk_progress_bar_set_fraction(GTK_PROGRESS_BAR(progressbar), 0);
}


but what should I do if I want to modify any other variables in this
function as well? let's say that in the part where I created the
g_signal_connect there are also some variables A and B which might be of
interest in clear_timer_cb. 

should I create a struct

struct data {
  gdouble *A;
  gdouble *B;
  GtkWidget *progressbar
};

and then initiate it and pass it always on?

what's the best way in dealing with this?

cheers,
Andreas