glibc hash table example

hash-table.c

/**
 * Compile with -D_GNU_SOURCE 
 * Note: we're using static keys here and we don't plan to add
 *       new items to the table. In such case using a perfect
 *       hash generator (e.g, gperf) would clearly outperform
 *       this simple example w/ the cost of first running gperf
 *       (and other tradeoff that must be considered)
 * 
 * Note: it's up to you to manage those resources contained in
 *       the hash table. Also, hsearch does NOT provide a 
 *       REMOVE action, only ENTER and FIND. If you with to 
 *       improve it with remove semantics you'll probably need
 *       to deal with it in the data-management side, 
 *       remembering that the table will keep only growing in
 *       space (there's no UPDATE action as well)
 */

#include <search.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

static char* keys[] = { "ciro", "hue", "br", "haha", "Lol" };
static char* values[] = { "cccc", "hhhh", "bbbb", "aaa", "oooo" };

typedef struct table_t {
  struct hsearch_data htab;
  size_t size;
} table_t;
#define TABLE_T_INITIALIZER                                                    \
  (table_t)                                                                    \
  {                                                                            \
    .htab = (struct hsearch_data){ 0 }, .size = 0                              \
  }

table_t* table_create(size_t size)
{
  table_t* table = malloc(sizeof(*table));

  *table = TABLE_T_INITIALIZER;
  hcreate_r(size, &table->htab);

  return table;
}

void table_destroy(table_t* table)
{
  hdestroy_r(&table->htab);
  free(table);
  table = NULL;
}

int table_add(table_t* table, char* key, void* data)
{
  unsigned n = 0;
  ENTRY e, *ep;

  e.key = key;
  e.data = data;
  n = hsearch_r(e, ENTER, &ep, &table->htab);

  return n;
}

void* table_get(table_t* table, char* key)
{
  unsigned n = 0;
  ENTRY e, *ep;

  e.key = key;
  n = hsearch_r(e, FIND, &ep, &table->htab);

  if (!n)
    return NULL;

  return ep->data;
}

int main(int argc, char* argv[])
{
  unsigned i = 0;
  table_t* table = table_create(10);
  void* d = NULL;

  if (argc < 2) {
    fprintf(stderr, "%s\n", "Usage: ./hash-tables <name>\n");
    exit(EXIT_FAILURE);
  }

  for (; i < table->size; i++)
    table_add(table, keys[i], values[i]);

  if ((d = table_get(table, argv[1])) != NULL)
    fprintf(stdout, "%s\n", (char*)d);
  else
    fprintf(stdout, "%s\n", "Not found :(");

  table_destroy(table);

  return 0;
}

After line 40, must set size into table, otherwise will affect line 90, table->size will always be 0 => table->size = size;
At line 82, table create 10 item is fine, but at line 90, will access out of keys[] array.
So line 82 should fix to 5

Reworked code is here https://github.com/novaua/ExpC/blob/master/glibc_hash_tbl/main.c
This includes the mentioned above fixes and improved memory management.