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From: nathan@elberton.inmos.co.uk (Nathan Sidwell)
Newsgroups: comp.lang.c
Subject: Re: Is #define THING -10 completely safe?
Message-ID: <12924@wraxall.inmos.co.uk>
Date: 31 Jan 91 12:59:10 GMT
References: <33@christmas.UUCP> <14998@smoke.brl.mil>
Sender: news@inmos.co.uk
Reply-To: nathan@inmos.co.uk (Nathan Sidwell)
Organization: INMOS Limited, Bristol, UK.
Lines: 42

In article <14998@smoke.brl.mil> gwyn@smoke.brl.mil (Doug Gwyn) writes:
>In article <33@christmas.UUCP> rtm@island.COM (Richard Minner) writes:
>>Something I've been curious about, should the above be
>>#define INT_MIN   (-2147483648)
>
>Yes.
>
>>The precedence rules seem to imply that ()'s aren't needed
>>with a negative integer constant.
>
>There are contexts that could cause trouble, e.g. "x-INT_MIN"
>or "x=INT_MIN".  While the C standard requires that these work
>as expected, many older C implementations will misinterpret
>these.

Well gcc -ansi doesn't, 
source is

#define NUM -10
main()
{
  int x;
  x = x-NUM;
  x = 1/**/2;
}

preprocessor output is

main()
{
  int x;
  x = x--10;
  x = 1 2;
}

which fails, note that it is partly correct as
the /**/ has been reduced to a space. This is gcc 1.36, has it been
fixed in later versions?

Nathan Sidwell, INMOS Ltd, UK         JANET:    nathan@uk.co.inmos
Generic disclaimer applies            UUCP:     ukc!inmos!nathan
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