From owner-freebsd-questions  Sat Sep  1 14:45: 6 2001
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From: Archie Cobbs <archie@dellroad.org>
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Subject: Re: gcc -D flag
In-Reply-To: <20010901234003.A14485@student.uu.se> "from Erik Trulsson at Sep
 1, 2001 11:40:03 pm"
To: Erik Trulsson <ertr1013@student.uu.se>
Date: Sat, 1 Sep 2001 14:44:22 -0700 (PDT)
Cc: freebsd-questions@freebsd.org
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Erik Trulsson writes:
> > Can someone tell me what I'm missing here?
> > 
> >     $ cat > foo.c
> >     int main(int ac, char **av) { return 0; }
> >     #if FOO == BAR
> >     #error
> >     #endif
> >     $ cc -o foo -Wall -DFOO=BAR foo.c
> >     foo.c:3: #error 
> >     $ cc -o foo -Wall foo.c
> >     foo.c:3: #error 
> >     $ cc -o foo -Wall -DFOO=NOTBAR foo.c
> >     foo.c:3: #error 
> > 
> > Seems like #if FOO == BAR is being evalutated as true no matter what.
> > 
> > This is with FreeBSD 4.3-REL, gcc 2.95.3.
> > 
> 
> The '==' operator works on numbers not strings. (This is true both for
> the preprocessor and 'normal' C.)
> The preprocessor considers all tokens that are undefined to have the
> numeric value 0.
> 
> So in all three cases you actually end up with
> #if 0 == 0
> #error
> #endif
> 
> Try using -DFOO=7 -DBAR=75 or some other number(s) instead and see if
> things don't work better. (They should.)

Thanks! That did it.

-Archie

__________________________________________________________________________
Archie Cobbs     *     Packet Design     *     http://www.packetdesign.com

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