6-class/structure/hashtable.h

// Simple hash table implemented in C.
// From: https://github.com/benhoyt/ht

#ifndef _HT_H
#define _HT_H

#include <stdbool.h>
#include <stddef.h>

// Hash table structure: create with ht_create, free with ht_destroy.
typedef struct ht ht;

// Hash table entry (slot may be filled or empty).
typedef struct {
    const char* key;  // key is NULL if this slot is empty
    void* value;
} ht_entry;

// Hash table structure: create with ht_create, free with ht_destroy.
struct ht {
    ht_entry* entries;  // hash slots
    size_t capacity;    // size of _entries array
    size_t length;      // number of items in hash table
};

ht* ht_create(void);
void ht_destroy(ht* table);

//  Get item with given key (NUL-terminated) from hash table. Return
// value (which was set with ht_set), or NULL if key not found.
void* ht_get(ht* table, const char* key);

// Set item with given key (NUL-terminated) to value (which must not
// be NULL). Return address of copied key, or NULL if out of memory.
const char* ht_set(ht* table, const char* key, void* value);

size_t ht_length(ht* table); // Return number of items

// Hash table iterator: create with ht_iterator, iterate with ht_next.
typedef struct {
    const char* key;  // current key
    void* value;      // current value

    // Don't use these fields directly.
    ht* _table;       // reference to hash table being iterated
    size_t _index;    // current index into ht._entries
} hti;

// Return new hash table iterator (for use with ht_next).
hti ht_iterator(ht* table);

// Move iterator to next item in hash table, update iterator's key
// and value to current item, and return true. If there are no more
// items, return false. Don't call ht_set during iteration.
bool ht_next(hti* it);

#endif // _HT_H