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Internet Message Format | 1996-08-05 | 1.5 KB

Path: anvil.ugrad.cs.ubc.ca!not-for-mail
From: [e-mail] (Kazimir Kylheku)
Newsgroups: comp.lang.c
Subject: Re: How are multidimensional array stored in memory?
Date: 1 Mar 1996 12:20:10 -0800
Organization: Computer Science, University of B.C., Vancouver, B.C., Canada
Message-ID: <[e-mail]>
References: <4h6tk6$[e-mail]>
NNTP-Posting-Host: anvil.ugrad.cs.ubc.ca

In article <4h6tk6$[e-mail]>,
Chris Rossall <[e-mail]> wrote:
>Hello I was just wondering how multidimensional arrays would be stored
>in memory.For example info[20][3].
>would infor[0][1] follow info[0][0] or would info[1][0] follow it?
>Perhaps this is compiler dependant?

It is not compiler dependent. The least significant portion of the address
depends on the very last index. Thus, the elements of info are stored in memory
in the order:

    info[0][0]
    info[0][1]
    info[0][2]
    info[1][0]
    .
    .
    .
    info[19][2]


This is easy to remember, since the least significant index is on the right
side. Another way to remember is that for incomplete array types, only the
leftmost index can be []. E.g.

char *twodim[][3] = {
    {  "Joe", "Smith", "programmer" },
    {  "Mary", "Jones", "engineer" },
    /* more triplets */
};

Of course, the inner braces can be elided.

In this case, twodim is an array of unspecified size (determined by the number
of initializers) of little three-membered arrays of char pointers.

Only one [] is ever allowed, must be the leftmost index, and can be present by
itself.
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