huschi.net

HCREATE(3P)                POSIX Programmer's Manual               HCREATE(3P)
PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
NAME
       hcreate, hdestroy, hsearch -- manage hash search table
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  shall  manage  hash
       search tables.
       The  hcreate()  function shall allocate sufficient space for the table,
       and the application shall ensure it is called before hsearch() is used.
       The  nel  argument is an estimate of the maximum number of entries that
       the table shall contain. This number may  be  adjusted  upward  by  the
       algorithm  in  order to obtain certain mathematically favorable circum-
       stances.
       The hdestroy() function shall dispose 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 hsearch() function is a hash-table search routine. It shall  return
       a  pointer  into a hash table indicating 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 comparison function used
       by hsearch() is strcmp().  The action argument is a member of  an  enu-
       meration type ACTION indicating the disposition of the entry if it can-
       not 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.
       These functions need not be thread-safe.
RETURN VALUE
       The  hcreate() function shall return 0 if it cannot allocate sufficient
       space for the table; otherwise, it shall return non-zero.
       The hdestroy() function shall not return a value.
       The hsearch() function shall return 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
       The hcreate() and hsearch() functions may fail if:
       ENOMEM Insufficient storage space is available.
       The following sections are informative.
EXAMPLES
       The following example reads in strings  followed  by  two  numbers  and
       stores  them  in  a hash table, discarding 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>
           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 string_space[NUM_EMPL*20];   /* Space to store strings. */
               struct info info_space[NUM_EMPL]; /* Space to store employee info. */
               char *str_ptr = string_space;     /* Next space in string_space. */
               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_ptr, &info_ptr->age,
                      &info_ptr->room) != EOF && i++ < NUM_EMPL) {
                   /* Put information in structure, and structure in item. */
                   item.key = str_ptr;
                   item.data = 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;
           }
APPLICATION USAGE
       The  hcreate()  and  hsearch()  functions  may use malloc() to allocate
       space.
RATIONALE
       None.
FUTURE DIRECTIONS
       None.
SEE ALSO
       bsearch(), lsearch(), malloc(), strcmp(), tdelete()
       The Base Definitions volume of POSIX.1-2008, <search.h>
COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and
       The  Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be  obtained  online
       at http://www.unix.org/online.html .
       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                          HCREATE(3P)