Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!newstop!male!matilda!harry
From: harry@matilda.uk.sun.com (Harry Protoolis - Sun EHQ)
Newsgroups: comp.lang.c
Subject: Re: Memory allocation / data access
Message-ID: <5654@male.EBay.Sun.COM>
Date: 15 Mar 91 17:47:33 GMT
References: <29491@cs.yale.edu>
Sender: news@male.EBay.Sun.COM
Reply-To: harry.protoolis@uk.1.com
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Organization: Sun Microsystems Europe Inc
Lines: 65

Jim,

You might be better of using pointers instead of constantly dereferencing array
elements.

cartesian *a_atom, b_atom;

for (a_atom = monomer[i].atom, k = 0; k < natoms; k++, a_atom++) {
    for (b_atom = monomer[j].atom, l = 0; l < natoms; l++, b_atom++) {
        xdis = a_atom->x - b_atom->x;
        ydis = a_atom->y - b_atom->y;
        zdis = a_atom->z - b_atom->z;
    }
}

Your allocation looks alright to me, though if you're allocating largish arrays
on a smallish system (e.g. > 64K on a PC) you might be better off using a
linked list. Oh, and why do you use malloc the first time and calloc the
next ?, as they are both array allocations you should, strictly speaking, be
using calloc for both.

if ((monomer = (solvent *) calloc (nmol, sizeof (solvent *)))==NULL)

Regards
Harry

|> typedef struct {
|>   double          x;
|>   double          y;
|>   double          z;
|> } cartesian;
|> 
|> typedef struct {
|>   cartesian       *atom;
|> } solvent;
|> 
|> solvent        *monomer;
|> 
|> /* Allocate the necessary storage */
|> 
|> if ((monomer = (solvent *) malloc (nmol * sizeof (solvent *)))==NULL)
|>   exit(1);
|> 
|> for (i = 0; i < nmol; i++) 
|>   if ((monomer[i].atom = (cartesian *) calloc (natoms,sizeof(cartesian)))==NULL)
|>     exit(1);
|> 
|> /* check components */
|> 
|> for (k = 0; k < natoms; k++) {
|>   for (l = 0; l < natoms; l++) {
|>     xdis = fabs (monomer[i].atom[k].x - monomer[j].atom[l].x);
|>     ydis = fabs (monomer[i].atom[k].y - monomer[j].atom[l].y);
|>     zdis = fabs (monomer[i].atom[k].z - monomer[j].atom[l].z);
|>   }
|> }

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