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Path: utzoo!watmath!clyde!rutgers!brl-adm!adm!moss@BRL.ARPA
From: moss@BRL.ARPA
Newsgroups: comp.lang.c
Subject: Re:  C preprocessor question
Message-ID: <4136@brl-adm.ARPA>
Date: Fri, 30-Jan-87 13:31:37 EST
Article-I.D.: brl-adm.4136
Posted: Fri Jan 30 13:31:37 1987
Date-Received: Sat, 31-Jan-87 07:06:26 EST
Sender: news@brl-adm.ARPA
Lines: 25

Brett Galloway writes...
 >I have a question about the C preprocessor.  I have the following code
 >fragment, which fails to compile on my system (4.2BSD):
 >
 >#define	GROUP(group,subgroup)	(((group) << 8) | (subgroup))
 >
 >#if	GROUP(0,0)
 >#endif
 >
 >The #if chokes for some reason.  Can anyone in comp.lang.c see my error?
 >If there is no error, is this a known bug of the 4.2BSD cpp?
The pre-processor defined macros are not evaluated by CPP.  In other
words,  "#if  GROUP(0,0)" is illegal because GROUP(0,0) has no value.
You might want to use:

if( GROUP(0,0) )
...

instead.  Or, maybe you meant to say:

#if defined( GROUP )
...
#endif

-moss