NetNews Usenet Archive 1992 #16/NN_1992_16.iso/spool/comp/lang/c/11728

Text File | 1992-07-29 | 2.8 KB | 69 lines

Newsgroups: comp.lang.c
Path: sparky!uunet!mdisea!mitchell
From: [e-mail] (Bill Mitchell)
Subject: Re: Pointers outside of array boundary
Message-ID: <[e-mail]>
Sender: [e-mail]
Bcc:  mitchell
Reply-To: [e-mail] (Bill Mitchell)
Organization: Motorola, Mobile Data Division - Seattle, WA
References: <[e-mail]> <mjd.712419017@hal> <[e-mail]>
Date: Wed, 29 Jul 1992 21:40:10 GMT
Lines: 55

in comp.lang.c, [e-mail] (M. J. Saltzman) said:


>In article <mjd.712419017@hal> [e-mail] (Sievan Janacziewski) writes:
>>>[about 1-based indexing]
>>[...]
>>If 0-based arrays are unclear to your correspondent, then he or she
>>should practice more, so that they become more familiar, rather than
>>resorting to obfuscation to cover his or her inadequacies as a programmer.
>
>While I agree with this sentiment in general, I also have been faced
>with the problem of implementing complicated combinatorial algorithms
>from specifications that describe the algorithms using a 1-based
>indexing scheme.  From a purely aesthetic point of view, re-expressing
>the alogirthms to use 0-based indexing *clearly and correctly* seems
>like a worthwhile goal, but practical considerations (like having to
>get the work done) often take priority, and kluges to fixup the
>results of index calculations often serve to obfuscate the code and
>introduce bugs.  In this case, wasting the 0th element of an array
>seems like a relatively small price to pay, if that's the only way
>to write 1-based code.
>

I agree.  So, apparently, would a couple of programmers named Kernighan
and Ritchie; who are generally regarded as having adequate programming
skills.

From k&r-2, pages 111 and 112:

static char daytab[2][13] = {
    {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
    {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
};
[...]
We started the array daytab with a column of zero so that the month numbers
can run from the natural 1 to 12 instead of 0 to 11.  Since space is not at
a premium here, this is clearer than adjusting the indices.

[ end of the quotes]

So, there are situations where 1-based arrays make good sense.  In those
situations, 1-based arrays should be used.

However, except for those special situations, zero-based arrays should be
used because that is what programmers maintaining the code will expect.

The decision between 1-based and 0-based arrays is a judgement call,
and that decision could be made either way depending on factors such
as maintainability considerations, ease of porting a previous implementation
from another language, implementing an algorithm from a published
description, etc.

--
[e-mail] (Bill Mitchell)