how to get a GdkGC of a GdkWindow

[Jiang XU <jiang xu echostar com>]

I try to use function:
                    gdk_window_copy_area(GdkWindow *window,
                                                                  GdkGC
*gc,
                                                                  gint
x,
                                                                  gint
y,

GdkWindow *source_window,
                                                                  gint
source_x,
                                                                  gint
source_y,
                                                                  gint
width,
                                                                  gint
height);

But I donnot know what  "gc" is? I mean, which GdkWindow it belongs?
ANd how I can get a GdkGC from a Gdkwindow or GdkPixmap?

Anybody who knows, please teach me ASAP!

Thanks

Jiang