_O_n_l_i_n_e _M_a_n_u_a_l           Library Functions             hsearch(3c)



NNNNAAAAMMMMEEEE
     hsearch, hcreate, hdestroy - manage hash search tables

SSSSYYYYNNNNTTTTAAAAXXXX
     ####iiiinnnncccclllluuuuddddeeee <<<<sssseeeeaaaarrrrcccchhhh....hhhh>>>>

     EEEENNNNTTTTRRRRYYYY ****hhhhsssseeeeaaaarrrrcccchhhh((((iiiitttteeeemmmm,,,, aaaaccccttttiiiioooonnnn))))
     EEEENNNNTTTTRRRRYYYY iiiitttteeeemmmm;;;;
     AAAACCCCTTTTIIIIOOOONNNN aaaaccccttttiiiioooonnnn;;;;

     iiiinnnntttt hhhhccccrrrreeeeaaaatttteeee((((nnnneeeellll))))
     uuuunnnnssssiiiiggggnnnneeeedddd nnnneeeellll;;;;

     vvvvooooiiiidddd hhhhddddeeeessssttttrrrrooooyyyy(((())))

DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
     _h_s_e_a_r_c_h is a hash-table search routine.  It returns a
     pointer into a hash table indicating the location at which
     an entry can be found.  _i_t_e_m is a structure of type EEEENNNNTTTTRRRRYYYY
     (defined in the <<<<sssseeeeaaaarrrrcccchhhh....hhhh>>>> header file) containing two
     pointers: _i_t_e_m._k_e_y points to the comparison key, and
     _i_t_e_m._d_a_t_a points to any other data to be associated with
     that key.  (Pointers to types other than void should be cast
     to pointer-to-void.) _a_c_t_i_o_n is a member of an enumeration
     type AAAACCCCTTTTIIIIOOOONNNN (defined in <<<<sssseeeeaaaarrrrcccchhhh....hhhh>>>>) indicating the disposi-
     tion of the entry if it cannot be found in the table.  EEEENNNNTTTTEEEERRRR
     indicates that the item should be inserted in the table at
     an appropriate point.  Given a duplicate of an existing
     item, the new item is not entered and _h_s_e_a_r_c_h returns a
     pointer to the existing item.  FFFFIIIINNNNDDDD indicates that no entry
     should be made.  Unsuccessful resolution is indicated by the
     return of a null pointer.

     _h_c_r_e_a_t_e allocates sufficient space for the table, and must
     be called before _h_s_e_a_r_c_h is used.  _n_e_l is an estimate of the
     maximum number of entries that the table will contain.  This
     number may be adjusted upward by the algorithm in order to
     obtain certain mathematically favorable circumstances.

     _h_d_e_s_t_r_o_y destroys the search table, and may be followed by
     another call to _h_c_r_e_a_t_e.

EEEEXXXXAAAAMMMMPPPPLLLLEEEE
     The following example will read in strings followed by two
     numbers and store them in a hash table, discarding dupli-
     cates.  It will then read in strings and find the matching
     entry in the hash table and print it out.

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

          struct info {       /* this is the info stored in table */
               int age, room; /* other than the key */
          };

          #define NUM_EMPL    5000    /* # of elements in search table */

          main( )
          {






                    /* space to store strings */
               char string_space[NUM_EMPL*20];
                    /* space to store employee info */
               struct info info_space[NUM_EMPL];
                    /* next avail space in string_space */
               char *str_ptr = string_space;
                    /* next avail space in info_space */
               struct info *info_ptr = info_space;
               ENTRY item, *found_item, *hsearch();
                    /* name to look for in table */
               char name_to_find[30];

               int i = 0;

               /* create table */
               (void) hcreate(NUM_EMPL);
               while (scanf("%s%d%d", str_ptr, &info_ptr->age,
                      &info_ptr->room) != EOF && i++ < NUM_EMPL) {

                    /* put info in structure, and structure in item */
                    item.key = str_ptr;
                    item.data = (void *)info_ptr;
                    str_ptr += strlen(str_ptr) + 1;
                    info_ptr++;

                    /* put item into table */
                    (void) hsearch(item, ENTER);
               }

               /* access table */
               item.key = name_to_find;
               while (scanf("%s", item.key) != EOF) {
                   if ((found_item = hsearch(item, FIND)) != NULL) {

                    /* if item is in the table */
                    (void)printf("found %s, age = %d, room = %d\n",
                         found_item->key,
                         ((struct info *)found_item->data)->age,
                         ((struct info *)found_item->data)->room);
                   } else {
                    (void)printf("no such employee %s\n",
                         name_to_find)
                   }
               }
               return 0;
          }

SSSSEEEEEEEE AAAALLLLSSSSOOOO
     Library Functions (3): bsearch, lsearch, malloc, tsearch

DDDDIIIIAAAAGGGGNNNNOOOOSSSSTTTTIIIICCCCSSSS
     _h_s_e_a_r_c_h returns a null pointer if either the action is FFFFIIIINNNNDDDD
     and the item could not be found or the action is EEEENNNNTTTTEEEERRRR and
     the table is full.

     _h_c_r_e_a_t_e returns zero if it cannot allocate sufficient space
     for the table.

NNNNOOOOTTTTEEEESSSS
     _h_s_e_a_r_c_h and _h_c_r_e_a_t_e use _m_a_l_l_o_c() to allocate space.






     Only one hash search table may be active at any given time.

March 1989                              TX Programmer's Reference