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From: rpw3@redwood.UUCP (Rob Warnock)
Newsgroups: net.lang.c
Subject: Re: Can #define `token-string' be empty?
Message-ID: <169@redwood.UUCP>
Date: Fri, 22-Feb-85 01:01:40 EST
Article-I.D.: redwood.169
Posted: Fri Feb 22 01:01:40 1985
Date-Received: Fri, 22-Feb-85 15:41:45 EST
References: <800003@acf4.UUCP> <151@cci-bdc.UUCP>
Organization: [Consultant], Foster City, CA
Lines: 24

+---------------
| > Is
| > 	#define	X
| > valid, i.e., can the `token-string' mentioned on page 207 of K&R be empty?
| Yes.  the default value of X is 1.  |	larry...
| uucp:  ..mit-eddie!cybvax0!cci-bdc!larry | arpa:  henrik@mit-mc.ARPA
+---------------

Well, almost, Larry. There is no "default" for a "#define"; the empty
token-string is perfectly legal. See K & R page 87 for an example of an
empty token-string (the "then" macro).

You are probably thinking of the case of a symbol defined on the "cc"
command line with no value, as in "cc -DFOO bar.c" which defines "FOO"
to be 1. But if it is given a value the value is used, even if empty,
as in "cc -DFOO= bar.c" which defines "FOO" to be empty, not 1.


Rob Warnock
Systems Architecture Consultant

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