Re: How can I trust in Objective-C?

[Gary Polhill]

Fabio Mascelloni wrote:
> 
> In the interface of one of my program's classes , I define an array of
> float values called local_y.After that I initialize it and print its
> content with a function called
> "printfRow" implemented in this way:
> 
> void printfRow(float *vect,unsigned dim)
> {
>     unsigned idx;
>     for (idx=0;idx<dim;idx++) printf ("%f ",*(vect+idx));
>     printf ("\n");
> }
> 
> Here's the output for an instance of dim 2 when I try to use its
> elements in a method defined int the same class
> 
> printfRow(local_y,2); // the output is   4.061603  3.941553
> 
> // now I try to write these values whithout using printfRow
> 
> printf ("First value : %f \n",*(local_y));             //the output is
> 452.150452
> printf ("Second value : %f \n",*(local_y+1));     //the output is
> 0.000000
> 

I thought this might be an array/pointer thing. Arrays are not the same
as pointers, but I must confess I am not 100% clear about the difference.

I have tried to reproduce your problem declaring local_y to be an array
and a pointer, but can't. Here's the output of my program

% pointer -b
Array: 4.0616 3.94155 
Pointer: 4.0616 3.94155 
Array   Pointer
=====   =======
4.0616  4.0616
3.94155 3.94155


Here's the code I used:

 
/* main.m */
 
#import <simtools.h>
#import "pointer.h"
 
int main (int argc, const char **argv) {
  Pointer *p;
 
  initSwarm(argc, argv);
  p = [Pointer create: globalZone];
  [p mallocPtr];
  [p setArrElement: 0 toValue: 4.061603];
  [p setArrElement: 1 toValue: 3.941553];
  [p setPtrElement: 0 toValue: 4.061603];
  [p setPtrElement: 1 toValue: 3.941553];
  [p print];
  exit(0);
}
 
/* pointer.h */
 
#include <objectbase/SwarmObject.h>
#include <stdio.h>
#include <errno.h>
 
#define ARRSZ 2
 
@interface Pointer: SwarmObject {
  float arr[ARRSZ];
  unsigned arrSz;
  float *ptr;
  unsigned ptrSz;
}
 
-(void)setArrElement: (unsigned)i toValue: (float)v ;
 
-(void)setPtrElement: (unsigned)i toValue: (float)v ;
 
-(void)setNumPtrElements: (unsigned)n ;
 
+(id)create: (id)aZone ;
 
-(void)mallocPtr ;
 
-(void)print ;
 
@end
 
/* pointer.m */
 
#include "pointer.h"
 
void printfRow(float *v, unsigned d) {
  unsigned i;
 
  for(i = 0; i < d; i++) {
    printf("%g ", *(v + i));
  }
  printf("\n");
}
 
@implementation Pointer
 
-(void)setArrElement: (unsigned)i toValue: (float)v {
  if(i >= 0 && i < arrSz) {
    arr[i] = v;
  }
  else {
    fprintf(stderr, "Array element out of bounds (0-%u): %u\n", arrSz, i);
  }
}
 
-(void)setPtrElement: (unsigned)i toValue: (float)v {
  if(i >= 0 && i < ptrSz) {
    *(ptr + i) = v;
  }
  else {
    fprintf(stderr, "Pointer element out of bounds (0-%u): %u\n", ptrSz, i);
  }
}
 
-(void)setNumPtrElements: (unsigned)n {
  ptrSz = n;
}
 
+(id)create: (id)aZone {
  Pointer *obj;
 
  obj = [super create: aZone];
  obj->ptrSz = 2;
  obj->arrSz = ARRSZ;
  return obj;
}
 
-(void)mallocPtr {
  ptr = (float *)malloc(ptrSz * sizeof(float));
  if(ptr == NULL) {
    perror("Memory allocation of ptr");
    exit(1);
  }
}
 
-(void)print {
  int i;
 
  printf("Array: ");
  printfRow(arr, arrSz);
  printf("Pointer: ");
  printfRow(ptr, ptrSz);
  printf("Array\tPointer\n");
  printf("=====\t=======\n");
  for(i = 0; (i < arrSz) && (i < ptrSz); i++) {
    printf("%g\t%g\n", *(arr + i), *(ptr + i));
  }
}
 
@end


-- 

Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen. AB15 8QH
Tel: +44 (0) 1224 318611               Email: address@hidden

                  ==================================
   Swarm-Support is for discussion of the technical details of the day
   to day usage of Swarm.  For list administration needs (esp.
   [un]subscribing), please send a message to <address@hidden>
   with "help" in the body of the message.