A quick demonstration on using khash to store string values allocated on the heap, and eventually freeing them after use

khash_strs.c

#include "khash.h"
#include <stdbool.h>
#include <stdio.h>

void gen_rand_string(char *buf, size_t buf_len, bool should_randomize_str_len) {
    static char charset[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

    size_t str_len = buf_len - 1;
    if (should_randomize_str_len)
        str_len = (rand() % str_len) + 1;

    for (size_t i = 0; i < str_len; i++) {
        int key = rand() % (int)(sizeof(charset) - 1);
        buf[i] = charset[key];
    }

    buf[str_len] = '\0';
}

KHASH_MAP_INIT_STR(str_to_str, char *)

int main() {
    const size_t key_buf_len = 4;  //max_key_len = key_buf_len - 1
    const size_t val_buf_len = 31; //max_val_len = val_buf_len - 1
    const bool should_randomize_key_len = false;
    const bool should_randomize_val_len = true;
    const unsigned max_items_to_insert = 10000;

    khash_t(str_to_str) *foo_hash_table = kh_init(str_to_str);

    unsigned items_inserted = 0;
    for (unsigned i = 0; i < max_items_to_insert; i++) {
        int absent;
        char *key_buf = calloc(key_buf_len, sizeof(char));
        char *val_buf = calloc(val_buf_len, sizeof(char));

        /* gen key & val */
        gen_rand_string(key_buf, key_buf_len, should_randomize_key_len);
        gen_rand_string(val_buf, val_buf_len, should_randomize_val_len);

        /* insert key */
        khiter_t new_item_it = kh_put(str_to_str, foo_hash_table, key_buf, &absent);

        /*
         * insert val
         * if key already present, kh_put places 0 into ret var
         * if key not present, kh_put places a non-zero value into ret var
        */
        if (absent) {
            kh_key(foo_hash_table, new_item_it) = key_buf;
            kh_val(foo_hash_table, new_item_it) = val_buf;
            items_inserted++;
        } else {
            free(key_buf);
            free(val_buf);
        }
    }

    printf("%d insertion attempts; %d duplicates; %d keys\n\n", max_items_to_insert, max_items_to_insert - items_inserted, items_inserted);

    /* iterate over items method 1, print 5 items only */
    const char *k, *v;
    int i = 5;
    kh_foreach(foo_hash_table, k, v, {
        fprintf(stdout, "%s -> %s\n", k, v);
        if (--i < 0) break;
    });

    /* free items then free table */
    /* also, iterate over items method 2 */
    for (khiter_t it = kh_begin(foo_hash_table); it != kh_end(foo_hash_table); ++it) {
        if (kh_exist(foo_hash_table, it)) {
            free((void *)kh_key(foo_hash_table, it));
            free((void *)kh_val(foo_hash_table, it));
        }
    }
    kh_destroy(str_to_str, foo_hash_table);
}