Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uunet!taumet!steve
From: steve@taumet.com (Stephen Clamage)
Newsgroups: comp.lang.c++
Subject: Re: parameter[][]
Message-ID: <376@taumet.com>
Date: 3 Aug 90 20:10:29 GMT
References: <1545@m1.cs.man.ac.uk>
Organization: Taumetric Corporation, San Diego
Lines: 29

jk@cs.man.ac.uk (John Kewley ICL) writes:
>One of our staff is whingeing about having to specify the size of all
>dimensions for a multidimensional array (beyond the first that is).
>Can anyone give me some good reasons why this is, so I can placate him.
>He claims that it can be done in C so why can't it be done in C++.

It can't be done in C either, and you should get him to put up or
shut up (that's American for "prove it's true or stop whingeing",
whatever "whingeing" may be).  This is specified in every C text I've
ever seen, including K&R 1, section 5.7.  ANSI C also requires it.

A specific example:  If you declare
	T x[n][m];
it means x is an array of n elements, each of which is an array of
m elements of type T.  When you then say
	j = x[i][j];
the compiler knows that each row contains an array of m elements,
so it multiplies m*sizeof(T) to get the size of each row in the
array, multiplies that by i to get the offset of the row, and then
adds j*sizeof(T) to get the final offset.  If you do not declare the
value of m, how do you find the start of any row beyond the 0th row?
You can't.
-- 

Steve Clamage, TauMetric Corp, steve@taumet.com

-- 

Steve Clamage, TauMetric Corp, steve@taumet.com