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HCREATE(3)               BSD Library Functions Manual               HCREATE(3)

NAME
     hcreate, hdestroy, hsearch -- manage hash search table

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <search.h>

     int
     hcreate(size_t nel);

     void
     hdestroy(void);

     ENTRY *
     hsearch(ENTRY item, ACTION action);

DESCRIPTION
     The hcreate(), hdestroy(), and hsearch() functions manage hash search tables.

     The hcreate() function allocates sufficient space for the table, and the application should ensure it
     is called before hsearch() is used.  The nel argument is an estimate of the maximum number of entries
     that the table should contain.  This number may be adjusted upward by the algorithm in order to obtain
     certain mathematically favorable circumstances.

     The hdestroy() function disposes of the search table, and may be followed by another call to hcreate().
     After the call to hdestroy(), the data can no longer be considered accessible.  The hdestroy() function
     calls free(3) for each comparison key in the search table but not the data item associated with the
     key.

     The hsearch() function is a hash-table search routine.  It returns a pointer into a hash table indicat-ing indicating
     ing the location at which an entry can be found.  The item argument is a structure of type ENTRY
     (defined in the <search.h> header) containing two pointers: item.key points to the comparison key (a
     char *), and item.data (a void *) points to any other data to be associated with that key.  The compar-ison comparison
     ison function used by hsearch() is strcmp(3).  The action argument is a member of an enumeration type
     ACTION 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.  FIND indicates that no entry
     should be made.  Unsuccessful resolution is indicated by the return of a NULL pointer.

     The comparison key (passed to hsearch() as item.key) must be allocated using malloc(3) if action is
     ENTER and hdestroy() is called.

RETURN VALUES
     The hcreate() function returns 0 if the table creation failed and the global variable errno is set to
     indicate the error; otherwise, a non-zero value is returned.

     The hdestroy() function does not return a value.

     The hsearch() function 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.

EXAMPLES
     The following example reads in strings followed by two numbers and stores them in a hash table, dis-carding discarding
     carding duplicates.  It then reads in strings and finds the matching entry in the hash table and prints
     it out.

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

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

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

     int
     main(void)
     {
             char str[BUFSIZ]; /* Space to read string */
             struct info info_space[NUM_EMPL]; /* Space to store employee info. */
             struct info *info_ptr = info_space; /* Next space in info_space. */
             ENTRY item;
             ENTRY *found_item; /* Name to look for in table. */
             char name_to_find[30];
             int i = 0;

             /* Create table; no error checking is performed. */
             (void) hcreate(NUM_EMPL);

             while (scanf("%s%d%d", str, &info_ptr->age,
                 &info_ptr->room) != EOF && i++ < NUM_EMPL) {
                     /* Put information in structure, and structure in item. */
                     item.key = strdup(str);
                     item.data = info_ptr;
                     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);
             }
             hdestroy();
             return 0;
     }

ERRORS
     The hcreate() and hsearch() functions may fail if:

     [ENOMEM]           Insufficient storage space is available.

     [EINVAL]           A table already exists.

SEE ALSO
     bsearch(3), lsearch(3), malloc(3), strcmp(3), tsearch(3)

STANDARDS
     The hcreate(), hdestroy(), and hsearch() functions conform to X/Open Portability Guide Issue 4,
     Version 2 (``XPG4.2'').

HISTORY
     The hcreate(), hdestroy(), and hsearch() functions first appeared in AT&T System V UNIX.

BUGS
     The interface permits the use of only one hash table at a time.

BSD                              July 6, 2008                              BSD