CS50 [Speller_hashtable] my hashtable is weird!

Question

After debugging for a long long time, it turned out that my hashtable must have some problem. Therefore, to find out where the problem is, I put this line of code after I insert a word in the hashtable. I suppose that this will print out just the first word in the first linked list. However, after I run my code, all the words in the dictionary are printed! Moreover, only words started with 'z' are fully printed, while other words, started with 'a' to 'y', are all printed "null" (just like the pictures below) By the way, whenever I run my code, the result always stops at MISSPELLED WORDS. Please help me figure this out! Thanks a lot!

printf("%s\n", hashtable[0]);

// Represents number of buckets in a hash table
#define N 26

// Represents a hash table
node *hashtable[N];

// Initializes sizeCounter
int sizeCounter = 0;

unsigned int hash(const char *word)
{
    return tolower(word[0]) - 'a';
}


// Loads dictionary into memory, returning true if successful else false
    bool load(const char *dictionary)
    {
        // Initialize hash table
        for (int i = 0; i < N; i++)
        {
            hashtable[i] = NULL;
        }

        // Open dictionary
        FILE *file = fopen(dictionary, "r");
        if (file == NULL)
        {
            unload();
            return false;
        }

        // Buffer for a word
        char word[LENGTH + 1];

        // Insert words into hash table
        while (fscanf(file, "%s", word) != EOF)
        {
            // Malloc a node* for each new word
            node *new_node = malloc(sizeof(node));
            if (new_node == NULL)
            {
                unload();
                return false;
            }

            // If it succeeds, copy the word into the node
            strcpy(new_node->word, word);

            // Insert into a linked list
            int hashCode = hash(word);
            printf("%i\n", hashCode);
            if (hashtable[hashCode] == NULL)
            {
                hashtable[hashCode] = new_node;
                new_node->next = NULL;
            }
            else
            {
                new_node->next = hashtable[hashCode];
                hashtable[hashCode] = new_node;
            }

            printf("%s\n", hashtable[0]);


            // Add 1 to count_size each time after inserting a word into a linked list
            sizeCounter++;

            // Free memory
            free(new_node);
        }

        // Close dictionary
        fclose(file);

        // Indicate success
        return true;
    }

// Returns true if word is in dictionary else false
bool check(const char *word)
{
    int l = strlen(word);
    char *tempWord = malloc(sizeof(char) * (l + 1));
    for(int i = 0; i < l; i++)
    {
        tempWord[i] = tolower(word[i]);
    }
    tempWord[l + 1] = '\0';

    node *cursor = hashtable[hash(tempWord)];

    // Check whether word is in dictionary
    while (cursor != NULL)
    {
        if (strcmp(tempWord, cursor->word) == 0)
        {
            free(tempWord);
            return true;
        }

        else
        {
            cursor = cursor->next;
        }
    }

    free(tempWord);
    // If word not in dictionary
    return false;
}

Answer 1

The code doesn't actually stop after MISSPELLED WORDS. It is actually going into an infinite loop. The line while (cursor != NULL) is looking for a NULL pointer value. Unfortunately, the nodes are not initialized when created, so the pointers contain garbage data. While that garbage data isn't a valid address, it's also not NULL. So, the while loop never ends. Hint: calloc() is your friend.

There are other problems that follow, but since you probably haven't had a chance to debug them, I'll leave it for you to find and fix them. If you can't, please open a new question and include the new code, including the node struct declaration.

If this answers your question, please click on the check mark to accept. Let's keep up on forum maintenance. ;-)