Question

I am new to C programming and I am getting confused with the pointer math. I have an array of characters of size 32. It is my understanding that this means that the array is also 32 bytes since a character variable is 1 byte big therefore 32 characters * 1 byte = 32 bytes. The problem is when having a function that has a void pointer that is pointing to an array of characters as described before. I believe that the code segment

for (count = 0; count < size; count++)
*((int*) raw_sk + count) = 0

should set all of the slots in the raw_sk buffer should be set to 0. However, when I run the program, I get a segmentation fault. I thought that it could be possibly be the fact that I am adding count to the address. I thought that if I were to add one to an address I would be moving to the next slot in the array. Can someone please point out where I am going wrong? The function I am using is below.
Thanks!

void
write_skfile (const char *skfname, void *raw_sk, size_t raw_sklen)
{
  int fdsk = 0;
  char *s = NULL;
  int status = 0;
  int count = 0;
  int size = (raw_sklen);


  /* armor the raw symmetric key in raw_sk using armor64 */
  s = armor64(raw_sk, raw_sklen);

  /* now let's write the armored symmetric key to skfname */

  if ((fdsk = open (skfname, O_WRONLY|O_TRUNC|O_CREAT, 0600)) == -1) {
    perror (getprogname ());

    /*scrubs the armored buffer*/
    for(count = 0; count < armor64len(s); count++)
    s[count] = '0';

    free (s);

    /* scrub the buffer that's holding the key before exiting */
   for (count = 0; count < size; count++)
    *((int*)raw_sk + count) = 0;

    exit (-1);
  }
  else {
    status = write (fdsk, s, strlen (s));
    if (status != -1) {
      status = write (fdsk, "\n", 1);
    }

   for (count = 0; (size_t)count < 22; count++)
    *((int*)raw_sk + count) = 0;

   free (s);
    close (fdsk);

    /* do not scrub the key buffer under normal circumstances
       (it's up to the caller) */ 

    if (status == -1) {
      printf ("%s: trouble writing symmetric key to file %s\n", 
          getprogname (), skfname);
      perror (getprogname ());

    /* scrub the buffer that's holding the key before exiting */

       /* scrub the buffer that's holding the key before exiting MY CODE
    for (count = 0; count < size; count++)
    *((int*)raw_sk + count) = 0;*/

      exit (-1);
    }
  }
}

Answer 1

You are incrementing the pointer by the size of an int. That is wrong. If you want to zero out the array you increment by the size of a char. Better yet, just use memset.