NetNews Usenet Archive 1992 #20/NN_1992_20.iso/spool/comp/std/c/2585

Internet Message Format | 1992-09-08 | 2.0 KB

Path: sparky!uunet!mcsun!uknet!acorn!ixi!clive
From: [e-mail] (Clive Feather)
Newsgroups: comp.std.c
Subject: Re: struct hack, was Re: strcpy implementation question
Message-ID: <[e-mail]>
Date: 7 Sep 92 10:49:32 GMT
References: <[e-mail]>
Organization: IXI Limited, Cambridge, UK
Lines: 28

In article <[e-mail]> [e-mail] (04-Sep-1992 1639) writes:
>In article <[e-mail]> [e-mail] (David Adrien Tanguay) writes:
>>[e-mail] (03-Sep-1992 1325) writes:
>>>In article <[e-mail]> [e-mail] (Israel Pinkas) writes:
>>>> The variable length struct is a hack.  There is nothing in the language that
>>>> prevents the compiler from performing bounds checking on accesses to name.
>>> Bounds checking is not allowed to affect output of a valid but ugly program.
>> I had the impression that the last time it came up here the conclusion was
>> that this trick was not sanctioned[...]  3.3.6 "Additive Operators"
>> says that you aren't guaranteed to go past the end of an array object,
> No (though it was the conclusion of some others) and yes, respectively.
> You can't go past the end of an array object.  But if malloc() or some other
> variable has defined the end of the actual array object, then the + operator
> can get you that far, regardless of the declared type that some other array
> variable had before getting flattened to a pointer.

But there is an intepretation that says that, given

    int a [5][5];

the access "a [1][6]" is illegal, because it goes past the bounds of the
array "a [1]". In other words, the declared type of the array does
restrict what can happen to a pointer derived from it.
--
Clive D.W. Feather     | IXI Limited         | If you lie to the compiler,
[e-mail]          | 62-74 Burleigh St.  | it will get its revenge.
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