0x1A-hash_tables

C - Hash tables

• What is a hash function
• What makes a good hash function
• What is a hash table, how do they work and how to use them
• What is a collision and what are the main ways of dealing with collisions in the context of a hash table
• What are the advantages and drawbacks of using hash tables
• What are the most common use cases of hash tables

0-hash_table_create.c

A function that creates a hash_table_t hash table

• Prototype: hash_table_t *hash_table_create(unsigned long int size);
  • where size is the size of the array
• Returns a pointer to the newly created hash table if success, otherwise returns NULL

1-djb2.c

A hash function implementing the djb2 algorithm

• Prototype: unsigned long int hash_djb2(const unsigned char *str);

2-key_index.c

A function that gives you the index of a key

• Prototype: unsigned long int key_index(const unsigned char *key, unsigned long int size);
  • where key is the key
  • size is the size of the array of the hash table
• This function uses the djb2 algorithm in 1-djb2.c
• Returns the index at which the key/value pair should be stored in the array of the hash table

3-hash_table_set.c

A function that adds an element to a hash_table_t hash table

• Prototype: int hash_table_set(hash_table_t *ht, const char *key, const char *value);
  • where ht is the hash_table_t hash table
  • key is the key(cannot be an empty string)
  • value is the value of the key
• Returns 1 if succeeded, 0 otherwise

4-hash_table_get.c

A function that retrieves tha value associated with a key

• Prototype: char *hash_table_get(const hash_table_t *ht, const char *key);
  • where ht is the hash table you want to look into
  • key is the key to be searched for
• Returns the value associated with the key or NULL if key could not be found

5-hash_table_print.c

A function that prints a hash_table_t hash table

• Prototype: void hash_table_print(const hash_table_t *ht);
  • ht is the hash table
• Prints the key/value pair in the order that tey appear in the array of the hash table in an array,list format
• Prints nothing if ht is NULL

6-hash_table_delete.c

A function that deletes a hash table

• Prototype: void hash_table_delete(hash_table_t *ht);
  • where ht is the hash table