Date: Fri, 4 Apr 1997 15:49:32 +0000 (   )
From: "Gurunandan R. Bhat" <grbhat AT unigoa DOT ernet DOT in>
To: William Heymann <heymann AT ucsu DOT Colorado DOT edu>
Cc: djgpp AT delorie DOT com
Subject: Re: Dynamic Allocation of Multidimensional Arrays
In-Reply-To: <33448D13.664@ucsu.Colorado.edu>
Message-Id: <Pine.LNX.3.91.970404153755.3631A-100000@aditya.unigoa.ernet.in>
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On Fri, 4 Apr 1997, William Heymann wrote:

> I was wondering how do I make an multi-dimensional array that itilalizes
> at run time without knowing any of the parameters. 

there are two ways that i know of heres the first, assuming that you want 
a two d array of size n X m of type int:
------------------------------------------------------------------
int **array;
int i, n, m;

array = (int **)malloc((unsigned int)(n * sizeof(int *)));

for (i = 0; i < n; ++i)
	array[i] = (int *)malloc((unsigned int)(m * sizeof(int)));
------------------------------------------------------------------

you can now refer to an int in this array by a[j][k] with j = 1...m and
i = 1...n. another way is by declaring a 1d array of size n*m and do the 
index book keeping yourself for example you can the a[j][k] mentioned 
above by a[j*n + k]. in one case the element is accessed by

*(*(a + j) + k)

and in the other case by 

*(a + (n*j + k))

i was around when two c purists were arguing on the relative merits of 
the two methods. i left and came back later to find them still at it ;)
i have heard it argued that the second is faster but the first is 
elegant. i'll let you know if they come to a conclusion. ;) 

> So how do I make a dynamic two dimensional array in C++?

use new instead of malloc

hope this helps,


gurunandan