printf and refresh drawing area

[Fabrice Chinjoie <fabrice chinjoie csiro au>]

Hi,

I want to see a semi circle moving into a drawing area.

That's what I do :

 gdk_draw_rectangle (widget->window,
             widget->style->white_gc,
             TRUE,
             0, 0,
              widget->allocation.width,
              widget->allocation.height);

 gdk_draw_arc(widget->window,
          widget->style->black_gc,
          TRUE,
          X,
          Y,
          dcircle,
          dcircle,
          angle*64,
          180*64);
change angle value...

This code is called by : timeout_handler =g_timeout_add(1000, 
update_angle,widget);

When I'm doing this, the drawing area doesn't change. But... If I put a 
printf(" angle %d \n",angle) after the gdk_draw_arc in the first 
function. it works and I can see my semi circle move.
Any idea about this?
Thanks.