/* This example was generated by Bob Beck and has been only lightly 
 * edited for presentation here.  The sample output was produced under 
 * CodeWarrior C/C++ compiler running on a PPC processor (not OpenBSD)
 * Students are free to download this example for testing purposes.
*/

#include<stdio.h>
#include<stdlib.h> /* for malloc() and friends. */

/* memory.c - A few examples of dynamic memory allocation for OpenBSD. 
 *
 * compile this program (g++ -Wall -ansi -o memory memory.c), then do a 
 *
 * setenv MALLOC_OPTIONS J
 * ./memory
 * 
 * The moral of the story is never trust malloc() to zero memory for you.
 * 
 */

#define CHUNKSIZE 10 /* we'll allocate this much at once */


int main() {
  int i, j; 
  char * fred;
  char * george;
  char * tmp;
  char sally[CHUNKSIZE];
  
  fred = (char *) malloc (CHUNKSIZE * sizeof(char));
  /* we must *always* check the return values of malloc and friends
   * - they will fail if inadequate memory space available 
   */
  if (fred == NULL) {
    fprintf(stderr, "Malloc barfed\n");
    exit(1);
  }
  george = (char *) calloc (CHUNKSIZE,  sizeof(char));
  if (george == NULL) {
    fprintf(stderr, "Calloc barfed\n");
    exit(1);
  }

  printf ("sally(%p), statically allocated has byte values: ", sally);
  for (i = 0; i < CHUNKSIZE; i++)
    printf("%d ", sally[i]);
  putchar('\n');
  
  printf ("fred(%p), from malloc has byte values: ", fred);
  for (i = 0; i < CHUNKSIZE; i++)
    printf("%d ", *(fred+i));		// this is also fred[i]
  putchar('\n');

  printf ("george(%p), from calloc has byte values: ", george);
  for (i = 0; i < CHUNKSIZE; i++)
    printf("%d ", *(george+i));		// this is also george [i]
  putchar('\n');

  
  /* grow george to make him CHUNKSIZE bigger */

  j = CHUNKSIZE + CHUNKSIZE;
  tmp = (char *) realloc(george, j * sizeof(char));
  if (tmp == NULL) {
    /* Important - when realloc fails, it returns NULL, but leaves
     * george unchanged (man 3 realloc for details) - if we had done: 
     * george = realloc(george, j * sizeof(char))
     * we would have lost the memory segment pointed to by george, since we
     * would have changed george's value to NULL. This doesn't matter
     * if our program is going to exit, but does matter if we are
     * going to continue and not have a memory leak.
     */
    fprintf(stderr, "realloc failed - george left unchanged\n"); 
    j = CHUNKSIZE;
  }
  else {
    george = tmp;
  }

  printf ("george(%p), from realloc has byte values: ", george);
  for (i = 0; i < j; i++)
    printf("%d ", george[i]);
  putchar('\n');

  /* we should free dynamically allocated memory when done with it */
  free(george);
  free(fred);
  
  /* but we don't free statically allocated memory - a
   * free(sally) will cause problems.
   */

  return (0);
}
/*	Sample output
sally(0x05dc9558), statically allocated has byte values: 0 0 0 0 0 0 0 9 5 -30 
fred(0x05d548b0), from malloc has byte values: 5 -43 72 -68 0 0 0 0 0 0 
george(0x05d548c0), from calloc has byte values: 0 0 0 0 0 0 0 0 0 0 
george(0x05d55860), from realloc has byte values: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 
*/