Date: Sat, 1 Sep 2001 14:44:22 -0700 (PDT) From: Archie Cobbs <archie@dellroad.org> To: Erik Trulsson <ertr1013@student.uu.se> Cc: freebsd-questions@freebsd.org Subject: Re: gcc -D flag Message-ID: <200109012144.f81LiMM54181@arch20m.dellroad.org> In-Reply-To: <20010901234003.A14485@student.uu.se> "from Erik Trulsson at Sep 1, 2001 11:40:03 pm"
next in thread | previous in thread | raw e-mail | index | archive | help
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 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200109012144.f81LiMM54181>