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Date: Mon, 13 May 2002 19:35:20 +0200
From: Jens Rehsack <rehsack@liwing.de>
Organization: LiWing IT-Services
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To: Paul Everlund <tdv94ped@cs.umu.se>
Cc: freebsd-questions@freebsd.org
Subject: Re: C malloc question
References: <Pine.GSO.4.33.0205131845160.22929-100000@gren.cs.umu.se>
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Paul Everlund wrote:
> 
> Hi all!
> 
> I have a question regarding malloc and returning arrays in C.
> 
> The following C program is an example.
> 
> #include <stdlib.h>
> #include <string.h>
> 
> static char *init()
> {
>   char *str;
>   int i;
> 
>   str = (char *)malloc(sizeof(char), 128);
malloc doesn't have 2 params
>   for(i = 0; i < 127; i++)
>     str[i] = "A";
>   str[i] = '\0';
>   return str;
> }
> 
> int main()
> {
>   int i;
> 
>   for(i = 0; i < 500000; i++)
>     init();
>   printf("%s\n", init());
>   return 0;
> }
> 
> This program takes up a lot of malloc'ed memory after a while,
> so how do one return arrays and free memory in the main function
> everytime the array have been used? I would like to not use fix-
> ed size arrays, as the real function should be general enough
> to handle all kind of array sizes.
> 
> As the size is known in the main function, I guess I could send
> in a buffer to get the data, as in init(char *buf), but I would
> like to avoid this.
> 
> What is the best solution for this problem?

Because it's a very small sample, I do not really see the goal...

Maybe a solution is

typedef struct object_t {
  size_t array_size
  char *ptr2array;
} object_t;

static int
init( struct object_t *obj )
{
  int rc = 0;
  if( object )
  {
    if( NULL != obj->ptr2array )
      free( obj->ptr2array );

    if( NULL != ( obj->ptr2array = calloc( WANTED_ARRAY_SIZE, sizeof(char) ) ) )
    {
      obj->array_size = WANTED_ARRAY_SIZE;
      ++rc;
    }
  }

  return rc;  
}
 
int
main(void)
{
  int i;
  object_t obj = { 0, NULL };

  for(i = 0; i < 500000; i++)
    init( &obj ); /* FIXME: check return code */

  printf( "%s\n", obj->ptr2array );

  return 0;
}
 
> Thanks a lot in advance!
> 
> Best regards,
> Paul
> 
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