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From: cjr@cs.bham.ac.uk (Chris Ridd <RiddCJ>)
Newsgroups: comp.lang.c
Subject: Re: Array bounds checking with C????
Message-ID: <988@christopher-robin.cs.bham.ac.uk>
Date: 30 Aug 90 10:21:50 GMT
References: <7611@ucdavis.ucdavis.edu> <26196@mimsy.umd.edu>
Reply-To: cjr@christopher-robin.UUCP (Chris Ridd <RiddCJ>)
Organization: University of Birmingham, England
Lines: 23

In article <26196@mimsy.umd.edu> chris@mimsy.umd.edu (Chris Torek) writes:
>In article <7611@ucdavis.ucdavis.edu> kuan@iris.ucdavis.edu
>(Frank [Who me?] Kuan) writes:
>>Why is it that most C compilers don't seem to [check array bounds]?
>
>Mostly because it is hard.  Given `int *p', is `p[-1] = 3' valid?
>That depends on the value of p....
>
>There is a company called Saber that produces a product called
>Saber-C that does this and more.  It works quite well, although last
>I had heard it still objected to `&arr[sizeof arr/sizeof *arr]',
>which is Officially Legal.  (Fortunately you can turn off each
>individual objection.)

  Why is this?  I never could figure out why accessing the first
element *past* the end of an array should be legal.

   Chris

-- Chris Ridd, Computer Science, Birmingham Uni, UK -- RiddCJ@Cs.Bham.Ac.Uk --

"'It's going to look pretty good, then, isn't it,' said War testily, 'the One
Horseman and Three Pedestrians of the Apocralypse.'" - Sourcery