From: Mat Hostetter <iclone!mjhostet AT cs DOT unm DOT edu>
Date: Tue, 13 Jul 93 04:24:47 -0600
To: djgpp AT sun DOT soe DOT clarkson DOT edu
Subject: Re: malloc problems

vincent AT physique DOT ens DOT fr (CROQUETTE Vincent) wrote:

> .... However, 

> you have to be carefuill when allocating a 2D array with DJGPP: the 

> allocation procedure work by chunk of power of 2 and if you  
allocate a 

> 512 element line, it needs 4 extra bytes for the record and thus  
reserve 

> a 1024 chunk ! Thus allocating a 512*512 array line by line will in  
fact
> freeze 2 times the expected size, with big array this turns out to  
be 

> dramatic. One way to overcome this pb is to allocate the big chunk 

> 512*512 in one operation and then map an array of pointers to  
begining 

> of lines.

There is no reason to use an array of pointers to the beginning of  
lines if you use the proper C types.  I believe this does what you  
want:


#define NROWS 512
#define NCOLS 512

typedef int row[NCOLS];
...
  row *my_matrix = (row *) malloc (sizeof (row) * NROWS);
  my_matrix[123][456] = 7;
...


-Mat