How do I know what signal triggered a callback?

["Daniel M. German" <dmg csg uwaterloo ca>]

well, I am learning that a selection one of radio button group in a
menu creates two callbacks: one to unselect the current selection and
one to select the new one. 

I am using GNOMEUIINFO_RADIOITEM_DATA to create the radio button and
attach automatically the callback.

The question is, can I know what signal triggered the callback?  If
so, how? 

thanks in advance for any help,



--
Daniel M. German                  "It is useless to punish a man
                                   unless he knows why he is punished...
                                   Punishment must be unusual
   R. Heinlein ->                  or it serves no purpose."
http://turingmachine.org/
dmg@csg.uwaterloo.ca