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From: debra@svin02.info.win.tue.nl (Paul de Bra)
Newsgroups: comp.lang.c
Subject: Re: Is #define THING -10 completely safe?
Message-ID: <1702@svin02.info.win.tue.nl>
Date: 29 Jan 91 11:15:44 GMT
References: <33@christmas.UUCP>
Organization: Eindhoven University of Technology, The Netherlands
Lines: 21

In article <33@christmas.UUCP> rtm@island.COM (Richard Minner) writes:
>In article <1991Jan23.015757.22220@portia.Stanford.EDU> fangchin@portia.Stanford.EDU (Chin Fang) writes:
>>... from my /usr/include/limits.h
>>#define INT_MIN     -2147483648  /* min decimal value of an "int" */

As James Clark reminded me a long time ago,
-2147483648 is a (constant) expression, not evaluated by the preprocessor
but by the compiler. This has 2 implications:
1) as people have said before, the replacement is purely textual, so the
   unary minus can be misused as a binary minus when writing something
   like 5 INT_MIN
2) this define is not supposed to work at all if 2147483648 is not a legal
   positive integer. (on most machines it isn't)
   if INT_MAX is 2147483647 then INT_MIN should not be written as
   -2147483648 but as (-2147483647-1)
   so your limits.h is at fault, and some compilers (including gcc)
   will not treat your INT_MIN as a large negative number, because
   of integral promotion. (2147483648 is promoted to unsigned because
   it is too large for a signed int)

Paul.
(debra@win.tue.nl, debra@research.att.com)