hsearch(3p) — Linux manual page


HCREATE(3P)               POSIX Programmer's Manual              HCREATE(3P)

PROLOG         top

       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         top

       hcreate, hdestroy, hsearch — manage hash search table

SYNOPSIS         top

       #include <search.h>

       int hcreate(size_t nel);
       void hdestroy(void);
       ENTRY *hsearch(ENTRY item, ACTION action);

DESCRIPTION         top

       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 circumstances.

       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 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.

       These functions need not be thread-safe.

RETURN VALUE         top

       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         top

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

       ENOMEM Insufficient storage space is available.

       The following sections are informative.

EXAMPLES         top

       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

           #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;

                   /* 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",
                           ((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;


       The hcreate() and hsearch() functions may use malloc() to allocate

RATIONALE         top




SEE ALSO         top

       bsearch(3p), lsearch(3p), malloc(3p), strcmp(3p), tdelete(3p)

       The Base Definitions volume of POSIX.1‐2008, search.h(0p)

COPYRIGHT         top

       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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                         HCREATE(3P)