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From: tarvaine@tukki.jyu.fi (Tapani Tarvainen)
Newsgroups: comp.sys.ibm.pc,comp.sys.intel
Subject: Re: correct code for pointer subtraction
Summary: Seems bug to me
Keywords: C pointers
Message-ID: <18123@santra.UUCP>
Date: 14 Dec 88 19:38:25 GMT
References: <597@mks.UUCP> <3845@pt.cs.cmu.edu>
Sender: news@santra.UUCP
Reply-To: tarvaine@tukki.jyu.fi (Tapani Tarvainen)
Organization: University of Jyvaskyla, Finland
Lines: 32

In article <3845@pt.cs.cmu.edu> ralf@b.gp.cs.cmu.edu (Ralf Brown) writes:
>In article <597@mks.UUCP> egisin@mks.UUCP (Eric Gisin) writes:
>-How come I can't find a compiler that generates correct
>-code for pointer subtraction in C on 8086s?
>-Neither Turbo, Microsoft, or Watcom do it right.

[stuff deleted]

>In addition to HUGE model, which someone already pointed out, I would like to
>mention that K&R only guarantees valid results for pointer subtractions 
>between pointers to the SAME array.

The same error occurs in the following program 
(with Turbo C 2.0 as well as MSC 5.0):

main()
{
        static int a[30000];
        printf("%d\n",&a[30000]-a);
}

output:  -2768

This seems perfectly legal according to either K&R or ANSI draft,
so I think this is a bug.



Tapani Tarvainen
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