How to get X window ID of a gtk window?

[Nils Philippsen <nils rhlx01 rz fht-esslingen de>]

Hello,

I wnated to know how one could get the X window id of a goven GTK window. I
need this to set a default icon the WM uses instead of an 'unknown
application'-icon. I found out that I must dig this way gtk_window ->
gdk_window -> X_window but it seems I'm not wit enough to find out the correct
member names to get the GDK window from the GTK and the X window from the GDK
window:-( (maybe there are some cast macros for this?)

Regards,
Nils
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Nils Philippsen                      @college: nils@rhlx01.rz.fht-esslingen.de
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D 70197 Stuttgart                     Do not meddle in the affairs of wizards,
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