hsearch(3C)                                              hsearch(3C)


       NAME
             hsearch, hcreate, hdestroy - manage hash search tables

       SYNOPSIS
             #include <search.h>
             ENTRY *hsearch (ENTRY item, ACTION action);
             int hcreate (size_t nel);
             void hdestroy (void);

       DESCRIPTION
             hsearch is a hash-table search routine generalized from Knuth
             (6.4) Algorithm D.  It returns a pointer into a hash table
             indicating the location at which an entry can be found.  The
             comparison function used by hsearch is strcmp [see
             string(3C)].  item is a structure of type ENTRY (defined in
             the search.h header file) containing two pointers: item.key
             points to the comparison key, and item.data points to any
             other data to be associated with that key.  (Pointers to types
             other than void should be cast to pointer-to-void.)  action is
             a member of an enumeration type ACTION (defined in search.h)
             indicating the disposition of the entry if it cannot be found
             in the table.  ENTER 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
             hsearch returns a pointer to the existing item.  FIND
             indicates that no entry should be made.  Unsuccessful
             resolution is indicated by the return of a null pointer.

             hcreate allocates sufficient space for the table, and must be
             called before hsearch is used.  nel 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.

             hdestroy destroys the search table, and may be followed by
             another call to hcreate.

          Return Values
             hsearch returns a null pointer if either the action is FIND
             and the item could not be found or the action is ENTER and the
             table is full.

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



                           Copyright 1994 Novell, Inc.               Page 1

      hsearch(3C)                                              hsearch(3C)


      USAGE
            The following example will read in strings followed by two
            numbers and store them in a hash table, discarding duplicates.
            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>
                  #include <string.h>
                  #include <stdlib.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;
                        /* 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 */


                          Copyright 1994 Novell, Inc.               Page 2

       hsearch(3C)                                              hsearch(3C)


                         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;
                   }

       REFERENCES
             bsearch(3C), lsearch(3C), malloc(3C), string(3C), tsearch(3C)

       NOTICES
             hsearch and hcreate use malloc(3C) to allocate space.

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

























                           Copyright 1994 Novell, Inc.               Page 3