#include <stdlib.h>    /* malloc       */

#include <stddef.h>    /* offsetof     */

#include <stdio.h>     /* printf       */

#include <string.h>    /* memset       */

#include "uthash.h"

struct inner {

    int a;

    int b;

}; 

struct my_event {

    struct inner is;           /* key is aggregate of this field */ 

    char event_code;           /* and this field.                */    

    int user_id;

    UT_hash_handle hh;         /* makes this structure hashable */

};

int main(int argc, char *argv[]) {

    struct my_event *e, ev, *events = NULL;

    unsigned i, keylen;

    keylen =   offsetof(struct my_event, event_code) + sizeof(char)                         

             - offsetof(struct my_event, is);

    for(i = 0; i < 10; i++) {

        e = (struct my_event*)malloc(sizeof(struct my_event));

        memset(e,0,sizeof(struct my_event));

        e->is.a = i * (60*60*24*365);          /* i years (sec)*/

        e->is.b = 0;

        e->event_code = 'a'+(i%2);              /* meaningless */

        e->user_id = i;

        HASH_ADD( hh, events, is, keylen, e);

    }

    /* look for one specific event */

    memset(&ev,0,sizeof(struct my_event));

    ev.is.a = 5 * (60*60*24*365);          

    ev.is.b = 0;

    ev.event_code = 'b';

    HASH_FIND( hh, events, &ev.is, keylen , e);

    if (e) printf("found: user %d, unix time %d\n", e->user_id, e->is.a);

   return 0;

}