Question

==3139== Conditional jump or move depends on uninitialised value(s)

==3139== at 0x4A0673F: strcpy (mc_replace_strmem.c:311)

==3139== by 0x400ADB: htable_insert (hashtable.c:56)

==3139== by 0x400F25: main (mylib.c:11)

Hi everybody, I’m still trying to insert into a hash table. I can’t quite get it to work, i’ve included my print method, just because i thought it might be a problem. I’m trying to do linear probing. When I ran valgrind, I got this error, I think it has something to do with copying into my string, but I’m not really sure what is means? I really don’t at this point know how to get this insertion working, some input would be wonderful..
Line 56 in hashtable insert is strcpy(str, key)

int htable_insert(htable h, char *str) {
   int i;
   /*convert string to integer*/
   unsigned int index = htable_word_to_int(str);
   /*calculate index to insert into hash table*/
   int remainder = index%h->capacity;
   /*once calculated position in the hash table, 3 possibilities occur*/
   /*no string in this positon, copy string to that position, increment number of keys, return 1*/
   if (h->key[remainder] == NULL) {
      char *key = emalloc(strlen(str) + 1);
      strcpy(str, key);
      h->key[remainder] = key;
      h->frequencies[remainder] = 1;
      h->num_keys++;
      return 1;
   }
   /*the exact same string is at the position, increment frequency at that position, return frequency*/
   if (strcmp(str, h->key[remainder]) == 0) {
      h->frequencies[remainder]++;
      return h->frequencies[remainder];
   }/*a string is at that position, but it isnt the rightone, keep moving along the array
      until you find either an open space or the string you are looking for*/
   if (h->key[remainder] != NULL && strcmp(str, h->key[remainder]) != 0) {
      /*you may need to wrap back around to the beginning of the table, so each time you add
        to the position you should also mod by the table capacity.*/
      for (i = 0; i <= h->capacity; i++) {
         /*no string in this positon, copy string to that position, increment number of keys*/
         if (h->key[remainder] == NULL) {
            char *key = emalloc(strlen(str) + 1);
            strcpy(str, key);
            h->key[remainder] = key;
            h->frequencies[remainder] = 1;
            h->num_keys++;
         }
         /*if you find the string you were looking for, increment the frequecny at the position
           and return the frequency*/
         if (strcmp(str, h->key[remainder]) == 0) {
            h->frequencies[remainder]++;
            return h->frequencies[remainder];
         }
         if (h->key[remainder] != NULL && h->capacity ==  i) {
            i = 0;
         }
      }   
   }
   /*if you have kept looking for an open space but there isnt one, the hash table must fu*/
   return 0;
}

void htable_print(htable h, FILE *stream) {
   int i;
   for(i = 0; i < h->capacity; i++) {
      if(h->key[i] != NULL) {
         fprintf(stream, "%d%s\n", h->frequencies[i], h->key[i]);
      }
   }
}

Answer 1

Your strcpy’s should be strcpy(key, str) and not the other way around. (You can just use strdup, btw, and save the malloc+strcpy).

Also, in:
if (h->key[remainder] != NULL && strcmp(str, h->key[remainder]) != 0) {

The condition “h->key[remainder] != NULL” is redundant: you’ve already checked that above.

Finally, in your loop (going over the buckets), it seems like:

1. The loop condition should be <, not <=
2. You should be incrementing remainder somewhere, or use “remainder+i” and the index to h->keys
3. Instead of “capacity==i” –> “i=0”, just use “(remainder+i)%capacity” as the index to h->keys

.. Finally finally — the initial part, the one that’s outside the loop, could be in the loop, saving code.