Man Pages

hcreate(3p) - phpMan hcreate(3p) - phpMan

Command: man perldoc info search(apropos)  


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 dif-
       fer (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  ta-
       ble  shall  contain.  This number may be adjusted upward by the algorithm in order to obtain certain mathemati-
       cally 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  appro-
       priate  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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  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 Stan-
       dard,  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)