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From: alen@cogen.UUCP (Alen Shapiro)
Newsgroups: comp.unix.questions
Subject: Summary Re: Brain-dead Unix tutor needs quick help (-1)
Message-ID: <391@cogen.UUCP>
Date: Fri, 20-Nov-87 15:40:40 EST
Article-I.D.: cogen.391
Posted: Fri Nov 20 15:40:40 1987
Date-Received: Mon, 23-Nov-87 04:14:45 EST
References: <387@cogen.UUCP> <6700@brl-smoke.ARPA>
Reply-To: alen@cogen.UUCP (Alen Shapiro)
Organization: Cogensys, LaJolla, Calf.
Lines: 38

Firstly, thanks to ALL who replied by mail and net. It seems that there
is no "knock-em-dead" reason for the statement

#define XXX (-1)

to have ()s round the "-1". i.e. On an ANSI standard C compiler (when one
is finally decided on :-)) there are NO situations where LEGAL use of XXX
results in a LEGAL program that differs in function with or without ()s
surrounding the "-1". Certainly antequated C compilers will probably
screw-up and make statements like a = XXX into a =- 1 (which (strictly
speaking) is no longer legal C).

There IS a reason for fully bracketing expressions within #define
since #define XXX a+b followed by y * XXX is probably not what is meant

There is also a reason for fully bracketing ALL pseudo variables within
preprocessor functions like #define XXX(a,b) ((a)+(b)) in case 'a' or 'b'
are expressions themselves when used in the code.

The closest to a REAL reason for not using #define XXX -1 came from
Steve Schlaifer who suggested that x= -XXX becomes x= --1 which unfortunately
is not legal C or it would have been a superb counter. There IS the case
where #define XXX -i (note the "i" not "1" here) which results in legal
C but does not answer the original question exactly. In this case there
is also an issue of good coding (what was the person doing with a global
variable manipulated from a #define - can you say "side-effect").

The answer I will use in this case will be one of style. It is good practise
to ALWAYS bracket expressions in case they come back to bite you or you
happen to port through an old compiler. Always bracketing expressions
(it should become a habit) will save debugging time and the programmer
should not be concerned with special cases that are immune to the
specific effect (in case, being human, (s)he misses an important counter).

So, thanks again, I don't feel quite as much of an idiot now
(all I have to work on is being an a** hole :-))

--alen the Lisa slayer (it's a long story)