CODEWITHSUNDEEP
cstructhashtablecs50singly-linked-list
Mahmoud Ashraf
Mahmoud Ashraf

Reputation: 1

Searching a hash table with singly linked list in c

I'm new to C I'm trying to check if a word is in my hash table or not. But I'm getting a segmentation fault.

This is my code for the function It should return true if the word is found or false if not

bool check(const char *word)
{
    // Hashing the word
    unsigned int hc = hash(word);
    // Creating a node for traversing
    node *ch = malloc(sizeof(node));
    // Traversing
    ch->next = table[hc];
    C = false;
    while (ch->next != NULL)
    {
        if (strcasecmp(ch->word, word) == 0)
        {
            c = true;
            break;
        }
        ch = ch->next;
    }
    return c;
}

Upvotes: 0

Views: 426

Answers (2)

Vlad from Moscow
Vlad from Moscow

Reputation: 310960

For starters neither the variable C used in this statement

C = false;

nor the variable c used in this statement

c = true;

are declared.

This allocation of a node

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

does not make a sense and produces a memory leak.

Also it is unclear whether for the given string the function hash returns a valid value of an index in the array table.

Provided that the function hash indeed returns a valid index then the function check can be defined the following way

bool check( const char *word )
{
    // Hashing the word
    unsigned int hc = hash( word );

    // Traversing
    node *head = table[hc];

    while ( head != NULL && strcasecmp( head->word, word ) != 0 )
    {
        head = head->next;
    }

    return head != NULL;
}

Upvotes: 1

M Oehm
M Oehm

Reputation: 29126

There are several issues with your code:

  • You only need to malloc when you create a node, for example when you insert an item into the table. If you just want to traverse the list in a bucket, create a pointer variable that visits all elements one by one. That variable is either a pointer to an existing node in the list or NULL.
  • When you traverse the list, you look at the nodes in isolation. You don't need to access next until you move to the next node.

Your function might look like this:

bool check(const char *word)
{
    unsigned int hc = hash(word);
    node *ch = table[hc];

    while (ch != NULL) {
        if (strcasecmp(ch->word, word) == 0) {
            return true;
        }

        ch = ch->next;
    }

    return false;
}

This should work provided that hash(word) produces valid hash table indices and that all head nodes of the bickets have been initialize to ´NULL`.

Upvotes: 0

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