Learning how to use khash (https://github.com/attractivechaos/klib/blob/master/khash.h)

khash_play.c

/* MIT License
 * Copyright (c) 2015 Genome Research Limited */

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

/*
  Learning how to use khash, focusing on string keys with string values

  Not tried:
  * Hash sets
  * kh_clear          reset a hash table without deallocating memory
  * kh_resize         resize a hash table
  * kh_begin          the start iterator (although used in kh_foreach)
  * kh_n_buckets      the number of buckets in the hash table
  * kh_foreach_value  iterate over the values in the hash table
*/

/* Initialise hash table type */
KHASH_MAP_INIT_STR(str_hash_t, const char*)

/* Print hash table */
void print_str_hash(khash_t(str_hash_t)* h) {
  const char* k;
  const char* v;

  kh_foreach(h, k, v, {
    (void)fprintf(stdout, "%s: %s\n", k, v);
  })
}

int main(int argc, char** argv) {
  /* Initialise hash table */
  khash_t(str_hash_t) *myHash = kh_init(str_hash_t);

  /* Print size of hash table (should be 0) */
  (void)fprintf(stdout, "size = %d\n", kh_size(myHash));

  /* Populate hash from argv */
  char** keys = malloc(argc * sizeof(char*));
  for (int i = 0; i < argc; ++i) {
    int ret;

    /* Create keys */
    *(keys + i) = malloc(10 * sizeof(char));
    (void)snprintf(*(keys + i), 10, "arg %d", i);

    /* Insert key */
    khiter_t newKey = kh_put(str_hash_t, myHash, *(keys + i), &ret);

    /* Set key value */
    kh_value(myHash, newKey) = *(argv + i);
  }

  /* Print hash table */
  print_str_hash(myHash);

  /* Print size of hash table (should be argc) */
  (void)fprintf(stdout, "size = %d\n", kh_size(myHash));

  /* Check "arg 0" exists (it should) and change it */
  {
    khiter_t arg0 = kh_get(str_hash_t, myHash, "arg 0");
    
    if (arg0 == kh_end(myHash)) {
      /* This shouldn't happen */
      (void)fprintf(stderr, "No such key\n");

    } else {
      /* We've got our key bucket, now check it contains data */
      if (kh_exist(myHash, arg0)) {
        int ret;

        /* Print the value */
        (void)fprintf(stdout, "Fetched \"%s\" value = %s\n",
                              kh_key(myHash, arg0),
                              kh_value(myHash, arg0));

        /* Change the value */
        const char* newValue = "Changed!";
        kh_value(myHash, arg0) = newValue;
        
        /* Print hash table */
        (void)fprintf(stdout, "\nCHANGED\n");
        print_str_hash(myHash);

        /* Delete "arg 0" */
        (void)kh_del(str_hash_t, myHash, arg0);

        /* Print hash table and size (should be argc - 1)*/
        (void)fprintf(stdout, "\nDELETED\n");
        print_str_hash(myHash);
        (void)fprintf(stdout, "size = %d\n", kh_size(myHash));

      } else {
        /* This shouldn't happen */
        (void)fprintf(stderr, "Key doesn't contain data\n");
      }
    }
  }

  /* Free */
  for (int i = 0; i < argc; ++i) { free(*(keys + i)); }
  free(keys);
  kh_destroy(str_hash_t, myHash);

  return 0;
}