NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part2/12016

Text File | 1996-08-05 | 1.5 KB | 61 lines

Path: news.channel1.com!channel1!dspse.bedford
Distribution: world
Newsgroups: comp.lang.c
Subject: Dynamic 2-D arrays
From: [e-mail] (Dspse Bedford)
Message-ID: <[e-mail]>
Date: Thu, 28 Mar 1996 06:28:00 -0640
Organization: Channel 1(R) 617-864-0100 Info

I want to define a 2-D array through a pointer-to-pointer structure member
as shown below:

typedef struct
{ float **matrix;}Obj;
main()
{Obj *m;
 int x=5;y=10;
 m=(Obj *)malloc(sizeof(Obj));
 *(m->matrix)=(float *)malloc(x*y*sizeof(float *));
  ...
 ...
 return;}

if I index in the following way: m->matrix[i][j], how does it increment the
pointer to determine the memory location?  If I have
m->matrix[1][2] and m->matrix[2][1] what is the difference?

In the past, I would use something like whats below, but the difference is
I do now know ahead of time the Y_dimension or the X_dimension.

#define Y_DIM 10
#define X_DIM  5
typedef struct
{float *matrix[Y_DIM];}Obj;
main()
{
  Obj *m;
  m=(Obj *)malloc(sizeof(Obj));
  for (i=0;i<Y_DIM;++i)
  { m->matrix[i]=(float *)malloc(X_DIM*sizeof(float));}
 ..
 return;}

The above ofcourse indexes fine since I create an array of pointers of the
proper Y-dimension in my structure definition.

Any help would be appreciated.

Thank you,
Anastasios Maurudis
[e-mail]
DSP Software Engineering, Inc.
175 Middlesex Turnpike
Bedford, MA 01730
[phone]
[phone] Fax


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