File content as of revision 5:142e66c8a7fa:

/*
 Student Name: Jaden Truxal
 Date: 3.23.19
 valgrind --leak-check=full ./ht_tests

=======================
ECE 2035 Project 2-1:
=======================
This file provides definition for the structs and functions declared in the
header file. It also contains helper functions that are not accessible from
outside of the file.

FOR FULL CREDIT, BE SURE TO TRY MULTIPLE TEST CASES and DOCUMENT YOUR CODE.

===================================
Naming conventions in this file:
===================================
1. All struct names use camel case where the first letter is capitalized.
  e.g. "HashTable", or "HashTableEntry"

2. Variable names with a preceding underscore "_" will not be called directly.
  e.g. "_HashTable", "_HashTableEntry"

  Recall that in C, we have to type "struct" together with the name of the struct
  in order to initialize a new variable. To avoid this, in hash_table.h
  we use typedef to provide new "nicknames" for "struct _HashTable" and
  "struct _HashTableEntry". As a result, we can create new struct variables
  by just using:
    - "HashTable myNewTable;"
     or
    - "HashTableEntry myNewHashTableEntry;"

  The preceding underscore "_" simply provides a distinction between the names
  of the actual struct defition and the "nicknames" that we use to initialize
  new structs.
  [See Hidden Definitions section for more information.]

3. Functions, their local variables and arguments are named with camel case, where
  the first letter is lower-case.
  e.g. "createHashTable" is a function. One of its arguments is "numBuckets".
       It also has a local variable called "newTable".

4. The name of a struct member is divided by using underscores "_". This serves
  as a distinction between function local variables and struct members.
  e.g. "num_buckets" is a member of "HashTable".

*/

/****************************************************************************
* Include the Public Interface
*
* By including the public interface at the top of the file, the compiler can
* enforce that the function declarations in the the header are not in
* conflict with the definitions in the file. This is not a guarantee of
* correctness, but it is better than nothing!
***************************************************************************/
#include "hash_table.h"


/****************************************************************************
* Include other private dependencies
*
* These other modules are used in the implementation of the hash table module,
* but are not required by users of the hash table.
***************************************************************************/
#include <stdlib.h>   // For malloc and free
#include <stdio.h>    // For printf


/****************************************************************************
* Hidden Definitions
*
* These definitions are not available outside of this file. However, because
* the are forward declared in hash_table.h, the type names are
* available everywhere and user code can hold pointers to these structs.
***************************************************************************/
/**
 * This structure represents an a hash table.
 * Use "HashTable" instead when you are creating a new variable. [See top comments]
 */
struct _HashTable {
  /** The array of pointers to the head of a singly linked list, whose nodes
      are HashTableEntry objects */
  HashTableEntry** buckets;

  /** The hash function pointer */
  HashFunction hash;

  /** The number of buckets in the hash table */
  unsigned int num_buckets;
};

/**
 * This structure represents a hash table entry.
 * Use "HashTableEntry" instead when you are creating a new variable. [See top comments]
 */
struct _HashTableEntry {
  /** The key for the hash table entry */
  unsigned int key;

  /** The value associated with this hash table entry */
  void* value;

  /**
  * A pointer pointing to the next hash table entry
  * NULL means there is no next entry (i.e. this is the tail)
  */
  HashTableEntry* next;
};


/****************************************************************************
* Private Functions
*
* These functions are not available outside of this file, since they are not
* declared in hash_table.h.
***************************************************************************/
/**
* createHashTableEntry
*
* Helper function that creates a hash table entry by allocating memory for it on
* the heap. It initializes the entry with key and value, initialize pointer to
* the next entry as NULL, and return the pointer to this hash table entry.
*
* @param key The key corresponds to the hash table entry
* @param value The value stored in the hash table entry
* @return The pointer to the hash table entry
*/
static HashTableEntry* createHashTableEntry(unsigned int key, void* value) {

//makes a new hashtable entry with a certain key, value and sets the next value to NULL
  HashTableEntry* htEntry = (HashTableEntry*)malloc(sizeof(HashTableEntry));
  if (!htEntry)
    return NULL;
  htEntry->key = key;
  htEntry->value = value;
  htEntry->next = NULL;

  return htEntry;

}

/**
* findItem
*
* Helper function that checks whether there exists the hash table entry that
* contains a specific key.
*
* @param hashTable The pointer to the hash table.
* @param key The key corresponds to the hash table entry
* @return The pointer to the hash table entry, or NULL if key does not exist
*/
static HashTableEntry* findItem(HashTable* hashTable, unsigned int key) {
  //finds an item in the hashtable using the key provided, if the item isn't in the hashtable, 
  int index = hashTable->hash(key);
  HashTableEntry* htEntry = hashTable->buckets[index]; 
  while(htEntry != NULL){
    if(htEntry->key == key){
      return htEntry;
    }
    htEntry = htEntry->next;
  }
  return NULL;
}

/****************************************************************************
* Public Interface Functions
*
* These functions implement the public interface as specified in the header
* file, and make use of the private functions and hidden definitions in the
* above sections.
****************************************************************************/
// The createHashTable is provided for you as a starting point.
HashTable* createHashTable(HashFunction hashFunction, unsigned int numBuckets) {
  // The hash table has to contain at least one bucket. Exit gracefully if
  // this condition is not met.
  if (numBuckets==0) {
    printf("Hash table has to contain at least 1 bucket...\n");
    exit(1);
  }

  // Allocate memory for the new HashTable struct on heap.
  HashTable* newTable = (HashTable*)malloc(sizeof(HashTable));

  // Initialize the components of the new HashTable struct.
  newTable->hash = hashFunction;
  newTable->num_buckets = numBuckets;
  newTable->buckets = (HashTableEntry**)malloc(numBuckets*sizeof(HashTableEntry*));

  // As the new buckets contain indeterminant values, init each bucket as NULL.
  unsigned int i;
  for (i=0; i<numBuckets; ++i) {
    newTable->buckets[i] = NULL;
  }

  // Return the new HashTable struct.
  return newTable;
}








void destroyHashTable(HashTable* hashTable) {
  //checks to make sure the hashtable has something in it
  if (hashTable == NULL){
    printf("Invalid Hash Table.");
  }
  //Goes through each bucket, freeing each value in each node and then the
  //node itself. After, it frees the buckets and the hashtable ptr itself
  HashTableEntry* next;
  int i;
  for(i = 0;i < hashTable->num_buckets; i++){
    HashTableEntry* htEntry = hashTable->buckets[i];
    while(htEntry != NULL){
      next = htEntry->next;
      //free node's value and ptr to node
      free(htEntry->value);
      free(htEntry);
      htEntry = next;
    }
  }
  free(hashTable->buckets);
  free(hashTable);

}








void* insertItem(HashTable* hashTable, unsigned int key, void* value) {
  int found = 0;
  void* retval = NULL;
  int index = hashTable->hash(key);
  //Test for a Null Hash Table
  if (hashTable == NULL){
    printf("Invalid Hash Table.");
    return NULL;
  }
  else{
    //See if value is in the list. if value is in the list, return the node's old value
    //and replace it with the new value that's read in
    HashTableEntry* htEntry;
    if((htEntry = findItem(hashTable, key))){
      found = 1;
      retval = htEntry->value;
      htEntry->value = value; 
    }


    
    //If entry wasn't found, create a new hash table entry for list 
    //and put it at beginning of list.
    if (!found){
      HashTableEntry* newHtEntry = createHashTableEntry(key, value);
      
      //If the llist isn't empty insert it at the beginning
      if(hashTable->buckets[index]){
        newHtEntry->next = hashTable->buckets[index];
      }
      //point the bucket ptr to the head of the new hashtable entry
      hashTable->buckets[index] = newHtEntry;
      retval = NULL;

    }
}
    return retval;
  }








  








  void* removeItem(HashTable* hashTable, unsigned int key) {
    void* retval = NULL;
  //Test for a Null Hash Table
    if (hashTable == NULL){
      printf("Invalid Hash Table.");
      return NULL;
    }
    else{
    
      int index = hashTable->hash(key);
    //if the item is found, return the value of it, set the 
      HashTableEntry* htEntry = hashTable->buckets[index];
      if(htEntry == NULL){
        return NULL;
      }
      else{
        if(htEntry->key == key){
          retval = htEntry->value;
          if(htEntry->next){
            hashTable->buckets[index] = htEntry->next;
          }
          else{
            hashTable->buckets[index] = NULL;
          }
          free(htEntry);
        }
        else{

          //keep track of previous 
          HashTableEntry* previous = htEntry;
          while (htEntry->next != NULL){
            previous = htEntry;
            htEntry = htEntry->next;
            if (htEntry->key == key){
              retval = htEntry->value;
              previous->next = htEntry->next;
              free(htEntry);
              break;
            }
          }
        }

      }

    }
    return retval;
  }






  void deleteItem(HashTable* hashTable, unsigned int key) {
    removeItem(hashTable, key);
  }