CODEWITHSUNDEEP
chashtable
yovelde
yovelde

Reputation: 1

Memory exception When inserting a value into a hash table

Memory exception When inserting a value into a hash table, I need to build a function that will insert values into my hash table but there is a memory problem because the chain threw me an anomaly I would love a solution

hashtable.h

struct HashTableElement
{
    int key;
    LinkedList* chain;
};

typedef struct HashTable HashTable;

struct HashTable
{
    HashTableElement* hashTable;
    int hashFunction;
    int tableSize;
    int cellsTaken;
    int numOfElements;
};

linked list.h

typedef struct LinkedList LinkedList;

struct LinkedList {
    char* data;
    LinkedList* next;
};

hash table.c

HashTable* initTable(int tableSize, int hashFunction)
{

    HashTable* table = (HashTable*)malloc(sizeof(HashTable));
    table->tableSize = tableSize;
    table->hashFunction = hashFunction;
    if (table == NULL || tableSize < 1)
    {
        printf("EROR with malloc in initTable.");
        exit(1);
    }
    table->hashTable = malloc(sizeof(HashTableElement) * tableSize);

    int i;
    for (i = 0; i < hashFunction; i++) {
        table->hashTable[i].key = NULL;
        table->hashTable[i].chain = NULL;
    }
    return table;
}
int insert(HashTable* ht, char* str)
{
    HashTable* temp;
    int h = hash(str, ht);
    int i = 0;
    while (ht->hashTable[h].key != 0 && (i < ht->tableSize)) {

        if (ht->hashTable[h].key == *str) {
            ht->hashTable[h].key = *str;
            return; /* break is intended to quit the loop, but actually we want to exit the function altogether */
        }

        h = (h + 1) % ht->tableSize; /* changed 11 to the size specified */
        i++; /* advance the loop index */
    }
    if (ht->hashTable[h].key == 0) {
        ht->hashTable[h].chain->data = *str;
        return 1;
    }
    return 0;
}

the problem with insert function in ht->hashTable[h].chain->data = *str; how I can solve the exception there?

Upvotes: 0

Views: 147

Answers (1)

Jurjen
Jurjen

Reputation: 11

I suggest to take a course in basic C programming before continuing with implementing a hash table. There are numerous errors and just generic weird things, of the top of my hat:

  • you are initializing an int (key) to NULL, which is a pointer.
  • you are initializing 'hashFunction' elements in a 'tableSize' array (wrong variable?)
  • you are only storing the first character of your string as a key.
  • the if statement where you check if your key is equal to the first character of your string, and, if it is, set it again to be equal to that, just in case before returning is ridiculous.
  • using 2 loop indices (both h and i seems superfluous).

Beyond these basic problems, the problem you are asking about is that chain will be NULL. If you use ...chain->data, you will dereference a NULL pointer, which is bad.

The real problem is that you don't seem to understand linked lists nor C memory management, which are a prerequisite for implementing more complicated structures, such as hash tables, so I would suggest you take a step back and start with a basic C course before continuing like this.

Upvotes: 1

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