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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 enumer-
       ation  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 reentrant. A function that is not required
       to be reentrant is not required to 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(), tsearch(), the Base Defini-
       tions volume of IEEE Std 1003.1-2001, <search.h>
COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open  Group.  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.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                          HCREATE(3P)