Pset5 check function, and probably load

Question

Ok...I'm doing pset5 and I'v already done the load function though I think there's something wrong with it.When I run speller it gives a seg fault in check function.Something to do with strcmp according to gdb.

After a looot of debugging, I'v found out that it crashes in the strcmp function and for some reason my second node of the first bucket..Um..first linked list in the array is this

"IN\000urgy\000\000ns\000\000m\000\000\000\000\000\000\000\000\000csilicovolcanoconiosis"

And here's my hash function, super simple I know, I'm gonna change it in the end.

int hashy(char* word){

 int num = (int)(toupper(word[0]) - 65);

 return num % 26;

}

And here's my load-

bool load(const char* dictionary)
{

FILE* dic = fopen(dictionary,"r");

//Make all the next pointers NULL
for(int j=0;j<26;j++){
 letters[j] = malloc(sizeof(node));
 letters[j]->next = NULL;
}

//Check if file could be opened
if(dic == NULL){

  printf("File not found, I repeat File not found");
  return false;

}

for(int i = 0;!feof(dic);i++){

  //new node
  node* new_node = malloc(sizeof(node));

  //get the word and store it in the node
  fscanf(dic,"%s",new_node->word);

  //first time
  if(letters[hashy(new_node->word)]->next == NULL){
    //letters[hashy(new_node->word)]->word = new_node->word;
    strcpy(letters[hashy(new_node->word)]->word,new_node->word);
    letters[hashy(new_node->word)]->next = new_node;
  }else{

    node* crawler = letters[hashy(new_node->word)]->next;

    while(!(crawler->next == NULL)){

     crawler = crawler->next;

    }

    crawler->next = new_node;

  }

  free(new_node);

}

fclose(dic);

return true;
}

And finally the check function-

bool check(const char* word)
{
char* worda = malloc(46);
strcpy(worda,word);

//find the wanted bucket
int buc = hashy(worda);

//loop through word
for(int i = 0,n = strlen(worda);i < n;i++){

if(isupper(worda[i])){
 tolower(worda[i]);
 }

}

node* crawler = letters[buc];

while(crawler != NULL){

  if(strcmp(crawler->word,worda) == 0){
  free(crawler);
  free(worda);
  return true;
      }

    crawler = crawler->next;

   }

    free(crawler);
    free(worda);
    return false;
}

Oh and the worda dosent get converted to lowercase letters in the function. I'v declared the letters array and struct node globally.Oh and here's what gdb shows in the end-

67      crawler = crawler->next;
(gdb) n
69     }
(gdb) 
59      while(crawler != NULL){
(gdb) 
61        if(strcmp(crawler->word,worda) == 0){
(gdb) 

Program received signal SIGSEGV, Segmentation fault.
__strcmp_sse4_2 () at ../sysdeps/i386/i686/multiarch/strcmp-sse4.S:217
217     movdqu  (%edx), %xmm2

Please do tell me what I'm doing wrong.

Answer 1

Does your load function even work? If not, that would explain the segfault (accessing illegal memory location) since there is no linked list to begin with.

Other points to consider:

1. Your hash function looks fine. Since you know dictionary words are all in lower case, you could've just left them as is and subtracted 97. No need for %26 either.
2. When you add new_node to your linked list in load, what does its next point to?
3. Consider whether you really need a crawler node in load, which, by the way, you did not malloc. Looks like the reason you included it because you want to add each successive entry to the end, rather than the beginning, of the list. However, your check function doesn't use a search algorithm to take advantage of a sorted list. If you don't plan on sorting the list, you might as well add new entries to the head of the list and do away with crawler. Or use a search algorithm in check, but be sure to free crawler.

Answer 2

bool load(const char* dictionary)
{

FILE* dic = fopen(dictionary,"r");

//Make all the next pointers NULL
for(int j=0;j<26;j++){
 letters[j]= NULL;
}

//Check if file could be opened
if(dic == NULL){

  printf("File not found, I repeat File not found");
  return false;

}

for(int i = 0;!feof(dic);i++){

  //new node
  node* new_node = malloc(sizeof(node));

  //get the word and store it in the node
  fscanf(dic,"%s",new_node->word);
  new_node->next = NULL; 

  //first time
  if(letters[hashy(new_node->word)]== NULL){

    letters[hashy(new_node->word)] = new_node;

  }else{

    node* crawler = malloc(sizeof(node));

    crawler = letters[hashy(new_node->word)];

    while(crawler->next != NULL){

     crawler = crawler->next;

    }

    crawler->next = new_node;
    free(crawler);

  }

}

    //TESTTTT

for(int i=0;i<26;i++){

node* ho = malloc(sizeof(node*));

ho = letters[i];

while(ho->next != NULL){

printf("ha_ha %s \n",ho->word);

ho= ho->next;

}

}

//TESTTTT


fclose(dic);

return true;

}

I'd added the test part to see if I'm loading it correctly but the while(ho->next != NULL)dosent get executed.