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 (con-
       sult 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 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  loca-
       tion  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 mem-
       ber of an enumeration type ACTION indicating the disposition of the entry if it cannot be found in the table. ENTER indi-
       cates 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 Definitions 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,  Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                   HCREATE(3P)