Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!gatech!gt-eedsp!baud
From: baud@gt-eedsp.UUCP (Kurt Baudendistel)
Newsgroups: comp.lang.c++
Subject: Re: Declaration of multi-dimensional arrays.
Message-ID: <430@gt-eedsp.UUCP>
Date: 6 Sep 88 15:05:54 GMT
References: <8809040943.AA28707@rice-chex.ai.mit.edu>
Reply-To: baud@gt-eedsp.UUCP (Kurt Baudendistel)
Organization: School of Electrical Engineering, Ga. Tech, Atlanta, GA  30332
Lines: 56

In article <8809040943.AA28707@rice-chex.ai.mit.edu> tmb@ganymede.UUCP 
discusses Doug Schmidts comments on the [] operator taking only one
argument and how this jives with easily implementable multi-dimensional
arrays.

it is possible to implement multi-dimensional arrays using the ``normal''
[] notations. to do this, you have to implement, dynamically, the array
dimensionality:

	md_array A(3);			// declare 3-d array

	A[0]		-> returns first 2-d array of A
			   type is ``2-d array''
	A[0][1]		-> return second 1-d array of previous
			   type is ``1-d array''
	A[0][1][2]	-> returns third element of previous
			   type is ``scalar'' (perhaps, double)

for me, this is just too inefficient. i use the following notation
in a vector (1-d) / matrix (2-d) implementation:

	doubleVec a(4);			// declare 4-element, 1-d array
					// of doubles

	a(0) *		-> returns first element of vector a
			   type is double
	a(0,1)		-> returns vector consisting of elements 0-1 of a
			   type is doubleVec

	doubleMat A(4,4);		// declare 4x4 element, 2-d array
					// of doubles

	A(0,0)		-> returns first element of array A 
			   type is double
	A(1) *		-> returns vector consisting of second row of A
			   type is doubleVec

i could, of course, have used the [] notation for the *'d example lines,
but i chose to use just the () notation, keeping the ``look'' and feel
of vectors and matrices all their own.  is this functional or operational
syntax in its usage here?  

note also that i could have used double [] notation A[0][0] to get
the first element of array A, but for efficiency reasons, i chose to 
use a single level operation of A(0,0) rather that the two-level
operation required to use [] twice.

you can argue about the merits of [] notation over () notation and
whether or not to allow multiple arguments to [], but i think that each 
has its place.

-- 
Kurt Baudendistel [GRA McClellan]
Georgia Tech, School of Electrical Engineering, Atlanta, GA  30332
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