#include <string.h>
#include <stdio.h>
#include <stdlib.h>
typedef size_t hash_size;
 struct hashnode_s {
        char *key;
        void *data;
        struct hashnode_s *next;
};
typedef struct hashtbl {
        hash_size size;
        struct hashnode_s **nodes;
        hash_size (*hashfunc)(const char *);
} HASHTBL;
static char *mystrdup(const char *s)
{
    char *b;
    if(!(b=malloc(strlen(s)+1))) return NULL;
    strcpy(b, s);
    return b;
}
static hash_size def_hashfunc(const char *key)
{
    hash_size hash=0;
    while(*key) hash+=(unsigned char)*key++;
    return hash;
}
HASHTBL *hashtbl_create(hash_size size, hash_size(*hashfunc)(const char *))
{
    HASHTBL *hashtbl;
    if(!(hashtbl=malloc(sizeof(HASHTBL)))) return NULL;      if(!(hashtbl->nodes=calloc(size, sizeof(struct hashnode_s*)))) {
        free(hashtbl);
        return NULL;
    }
    hashtbl->size=size;
    if(hashfunc) hashtbl->hashfunc=hashfunc;
    else hashtbl->hashfunc=def_hashfunc;
    return hashtbl;
}

int hashtbl_insert(HASHTBL *hashtbl, const char *key, void *data)
{
    struct hashnode_s *node;
    hash_size hash=hashtbl->hashfunc(key)%hashtbl->size;    
    node=hashtbl->nodes[hash];
    while(node) {
        if(!strcmp(node->key, key)) {
            node->data=data;
            return 0;
        }
        node=node->next;
                  }
    if(!(node=malloc(sizeof(struct hashnode_s)))) return -1;
    if(!(node->key=mystrdup(key))) {
        free(node);
        return -1;
    }
    node->data=data;      /*this data should point to the another hash table*/
    node->next=hashtbl->nodes[hash];
    hashtbl->nodes[hash]=node; 
    return 0;
}
void *hashtbl_get(HASHTBL *hashtbl, const char *key)
{
    struct hashnode_s *node;
    hash_size hash=hashtbl->hashfunc(key)%hashtbl->size;
    node=hashtbl->nodes[hash];
    while(node) {
        if(!strcmp(node->key, key)) return node->data;
        node=node->next;
    }
       return NULL;
}

int main()
{

HASHTBL *hashtbl;
    if(!(hashtbl=hashtbl_create(16, NULL))) {
                fprintf(stderr, "ERROR: hashtbl_create() failed\n");
                exit(EXIT_FAILURE);
        }
 hashtbl_insert(hashtbl, "Sports", "cricket");
 printf("After insert:%s\n",hashtbl_get(hashtbl, "Sports"));
return 0;
}

int main()
{
    HASHTBL *outer=hashtbl_create(16, NULL);
    HASHTBL *inner=hashtbl_create(16, NULL);
    hashtbl_insert(inner, "sports", "cricket");
    hashtbl_insert(outer, "sports_table", inner);

    {
      HASHTBL *inner=hashtbl_get(outer, "sports_table");
      const char *str=hashtbl_get(inner, "sports");

      printf("got %s\n", str);
    }
}