C preprocessor question

[moss at BRL.ARPA]

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