Re: What's wrong with my button callback

[David Nečas (Yeti) <yeti physics muni cz>]

On Thu, Jun 29, 2006 at 07:49:43PM +1000, kadil wrote:
> I used glade to "build" some a simple app. Why does my
> on_button1_clicked callback segfault. The very same function call works
> in the expose event.

Nothing in on_drawingarea1_expose_event() uses the
global variable drawingarea1, so they are not quite the
same.  It's probably uninitialized when on_button1_clicked()
is called (note global variables are generally frowned upon,
you can easily attach the pixmap to the drawing area with
g_object_set_data() and also pass the drawing area as the
callback data of on_button1_clicked() completely eliminating
global variables).

Did you try to use a debugger before mailing to the list?
Or valgrind?  What did you find?  If the cause really is
uninitialized drawingarea1, you would find it very easily
yourself.

> #ifdef HAVE_CONFIG_H
> #  include <config.h>
> #endif
>
> #include <gtk/gtk.h>
>
> #include "callbacks.h"
> #include "interface.h"
> #include "support.h"
> static GdkPixmap *pixmap = NULL;
> GtkWidget *drawingarea1;
>
> void
> on_button1_clicked                     (GtkButton       *button,
>                                         gpointer         user_data)
> { 
>  
>       gdk_draw_rectangle(pixmap, drawingarea1->style->black_gc,TRUE,50,
> 50,99, 88);
>  
> }
>
> gboolean
> on_drawingarea1_expose_event           (GtkWidget       *widget,
>                                         GdkEventExpose  *event,
>                                         gpointer         user_data)
> {
> gdk_draw_drawable(widget->window, widget->style->fg_gc[GTK_WIDGET_STATE
> (widget)], pixmap,  event->area.x, event->area.y,  event->area.x,
> event->area.y, event->area.width, event->area.height);
>   return FALSE;
> }

Yeti


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