You can give the '-#' command to the AIX compilers to see which 'language 
processing commands' would be invoked. I see _AIX, _AIX31, _AIX41, _IBMR2, 
and _POWER.

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>From: Jaromir Dolecek
>To: current-users
>Subject: Off topic: AIX q
>Date: September 1, 1997 6:50PM
>
><<File Attachment: HEADER.TXT>>
>
>Sorry for off topic mail, but this is one of handful mail groups I'm
>in and one of two the best to ask for this particular thing.
>
>Does AIX's cpp define some nice constant to recognize I'm compiling on
>AIX ? ``#ifdef unix'' works for any other system I've tried, but it
>fails miserably on AIX ;-( After I define symbol ``unix'' explicitly, all
>my code compiles cleanly, the problem is just to find out if I have to do
>so.
>
>It claims it's ``AIX version 4'' if I telnet on it.
>
>Thanks a lot for any help.
>
>jd
>--
>Jaromir Dolecek                        UVT MU, Botanicka 68A, Brno, 60200
>dolecek@ics.muni.cz               Tel.: +420-5-4151 2280
>http://www.muni.cz/~dolecek
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>Contrary to popular belief, Unix is user friendly.
>It just happens to be selective about who it makes friends with. -- Dave
>Parnas
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>