CODEWITHSUNDEEP
c++functionhashtablechaining
Vish
Vish

Reputation: 383

C++ Hash Chaining Function

I am trying to build a Hash table and with what I have learned using online tutorials I have come up with the following code

#include <iostream>
#include <string>
#include <cstdlib>

using namespace std;
const int SIZE = 100;

int hash(string);

class Node
{
   public:
      Node();
      Node(string);
      int hash(int value);
   private:
      string data;
      Node* next;

   friend class HashTable;
};

Node::Node() {
  data = "";
  next = NULL;
}

Node::Node(string) {
  data = "";
  next = NULL;
}

int Node::hash(int value) {
   int y;
   y = value % SIZE;
}

class HashTable {
public:
    HashTable();
      HashTable(int);
      ~HashTable();
      void insertItem(string);
      bool retrieveItem(string);

private:
      Node* ht;
};

HashTable::HashTable() {
  ht = new Node[SIZE];
}

HashTable::HashTable(int max) {
  ht = new Node[max];
}

HashTable::~HashTable() {
   delete[] ht;
}

void HashTable::insertItem(string name) {
    int val = hash(name);
    for (int i = 0; i < name.length(); i++)
        val += name[i];
}

bool HashTable::retrieveItem(string name) {
    int val = hash(name);
    if (val == 0 ) {
        cout << val << " Not Found " << endl;
    }
    else {
        cout << val << "\t" << ht->data << endl;
    }
}

void print () {
    //Print Hash Table with all Values
}

int main() {

   HashTable ht;
   ht.insertItem("Allen");
   ht.insertItem("Tom");

   ht.retrieveItem("Allen");

   //data.hash(int val);
   //cout << ht;

   system("pause");
   return 0;
}


int hash(string val) {
    int key;
    key = val % SIZE;
}

I am trying to insert string values and validate if the name exists using the retrieveItem function. Also, how do I go about printing the HashTable with values.

Any help will be highly appreciated.

Vish

Upvotes: 0

Views: 4935

Answers (2)

Chuck Norrris
Chuck Norrris

Reputation: 384

just use stl hashmap or for threadsafe hashmap use intel thread building blocks library

Upvotes: 0

Jerry Coffin
Jerry Coffin

Reputation: 490603

There's quite a bit wrong here. Just glancing at a random spot in the middle of the code, I found:

Node::Node(string) {
  data = "";
  next = NULL;
}

This doesn't save the value of the string that was passed in. I'm guessing you really wanted something more like:

Node::Node(string value) : data(value), next(NULL) {}

The next thing I saw was:

int Node::hash(int value) {
   int y;
   y = value % SIZE;
}

This computes a value and puts it into y (a local variable) but doesn't return anything, so the value you've computed is immediately lost. If you attempt to use its return value, you get undefined behavior (actually, I don't remember for sure -- it seems like in C you get UB only if you try to use the return value, but in C++ it's UB to do this at all -- regardless of the technical details, though, it's clearly not what you want and needs to be fixed).

Like I said, I just glanced at one spot in the code and found though -- I doubt they're the only problems. The bottom line is that you probably need to back up a bit, figure out what each function is supposed to do, and go through them one by one and ensure each is doing what it's supposed to.

One other bit of advice: instead of dealing with dynamically allocating an array on your own, I'd used std::vector.

Upvotes: 1

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