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From: throopw@dg_rtp.UUCP (Wayne Throop)
Newsgroups: net.lang.c
Subject: Re: dynamic array parameters
Message-ID: <57@dg_rtp.UUCP>
Date: Thu, 26-Dec-85 13:36:47 EST
Article-I.D.: dg_rtp.57
Posted: Thu Dec 26 13:36:47 1985
Date-Received: Sat, 28-Dec-85 01:33:49 EST
References: <977@brl-tgr.ARPA>
Lines: 27

To reference an element of a variably sized multi-dimensional array,
David Tribble recommends

>  (*(a + i*d1 + j))    /* same as a[i][j]	*/

along with using macros to simplify, like so:

> #define index(a,i,j)  (*(a + i*d1 + j))
>  index(a, i, j)       /* same as a[i][j]	*/

Good idea.  I'd just like to note that, using pointer/array equivalence,
the somewhat complicated expression can be written a little less
confusingly, as

        a[i*d1 + j]

It might still be advisable to use the macro, but then again, maybe not.
The more-than-two-dimensional cases are still pretty confusing:

        a[(i*d1 + j)*d2 + k]

Also, I'd recommend declaring the formal "a" as "int a[]" rather than
"int *a", unless it is important for some reason to treat "a" as an
lvalue.
-- 
Wayne Throop at Data General, RTP, NC
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