how to active the modaless window

["rion10 (sent by Nabble.com)" <lists nabble com>]

I've 2 modaless window created by the following way:
a = gtk_window_new (GTK_WINDOW_DIALOG); 
gtk_window_set_modal (GTK_WINDOW (a), FALSE); 

b = gtk_window_new (GTK_WINDOW_DIALOG); 
gtk_window_set_modal (GTK_WINDOW (b), FALSE); 

in my application, how to active any one, let it to be top level? Thanks!
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Sent from the Gtk+ - Apps Dev forum at Nabble.com:
http://www.nabble.com/how-to-active-the-modaless-window-t560520.html#a1505197