Re: Passing Struct to g_signal_connect

["Till Harbaum / Lists" <lists harbaum org>]

Hi,

you have to make sure that the parameters of your callback function
exactly match what's been described for this particular event. In your
case your have to check the "clicked" event for a GtkButton which gives
us:

void user_function(GtkButton *button, gpointer   user_data)  

So this is how your callback function should look like:
void on_button2_clicked(GtkButton *button, struct allStructs *by_ptr)

Your struct should be the _second_ parameter and not the first (any only)
one your made it. What you did is: You got a pointer to the GtkButton structure 
of your button and used _that_ as a pointer to your own struct. You
are likely messing up the Button structure ...

This is one ugly thing with the C bindings and the fact that everything
is just casted by this G_CALLBACK() macro. That way the compiler isn't
able to check these things and errors like yours happen. And these can
be very nasty bugs since they cause people to write to memory they
are not supposed to write to. A classic door for hackers ...

Till

Am Sonntag 19 Oktober 2008 schrieb beginner.c:
> I need to pass a struct using g_signal_connect, but the issue I'm having is
> that I can't alter the elements of the struct within the called function
> e.g.
>
> void on_button2_clicked (struct allStructs *by_ptr)
>
> {
>       gtk_label_set_text ((GtkLabel*)by_ptr->widgets.label, "whatever");
> }
>
> main
> {
> blah blah
> struct allStructs baseStruct;
>
> g_signal_connect (G_OBJECT(baseStruct.widgets.nextButton), "clicked",
> G_CALLBACK (on_button2_clicked), &baseStruct);
> }
>
> Any idea's? If I pass this struct to any other function I have no problem
> performing functions like in the callback. For some reason, I can't in the
> callback.