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.\" $FreeBSD: src/lib/libc/stdlib/hcreate.3,v 1.2 2001/07/09 15:54:36 ru Exp $

.\"

.Dd May 8, 2001

.Os

.Dt HCREATE 3

.Sh NAME

.Nm hcreate , hdestroy , hsearch

.Nd manage hash search table

.Sh LIBRARY

.Lb libc

.Sh SYNOPSIS

.In search.h

.Ft int

.Fn hcreate "size_t nel"

.Ft void

.Fn hdestroy void

.Ft ENTRY *

.Fn hsearch "ENTRY item" "ACTION action"

.Sh DESCRIPTION

The

.Fn hcreate ,

.Fn hdestroy ,

and

.Fn hsearch

functions manage hash search tables.

.Pp

The

.Fn hcreate

function allocates sufficient space for the table, and the application should

ensure it is called before

.Fn hsearch

is used.

The

.Fa nel

argument is an estimate of the maximum

number of entries that the table should contain.

This number may be adjusted upward by the

algorithm in order to obtain certain mathematically favorable circumstances.

.Pp

The

.Fn hdestroy

function disposes of the search table, and may be followed by another call to

.Fn hcreate .

After the call to

.Fn hdestroy ,

the data can no longer be considered accessible.

.Pp

The

.Fn hsearch

function is a hash-table search routine.

It returns a pointer into a hash table

indicating the location at which an entry can be found.

The

.Fa item

argument is a structure of type

.Vt ENTRY

(defined in the

.Aq Pa search.h

header) containing two pointers:

.Fa item.key

points to the comparison key (a

.Vt "char *" ) ,

and

.Fa item.data

(a

.Vt "void *" )

points to any other data to be associated with

that key.

The comparison function used by

.Fn hsearch

is

.Xr strcmp 3 .

The

.Fa action

argument is a

member of an enumeration type

.Vt ACTION

indicating the disposition of the entry if it cannot be

found in the table.

.Dv ENTER

indicates that the

.Fa item

should be inserted in the table at an

appropriate point.

.Dv FIND

indicates that no entry should be made.

Unsuccessful resolution is

indicated by the return of a

.Dv NULL

pointer.

.Sh RETURN VALUES

The

.Fn hcreate

function returns 0 if it cannot allocate sufficient space for the table;

otherwise, it returns non-zero.

.Pp

The

.Fn hdestroy

function does not return a value.

.Pp

The

.Fn hsearch

function returns a

.Dv NULL

pointer if either the

.Fa action

is

.Dv FIND

and the

.Fa item

could not be found or the

.Fa action

is

.Dv ENTER

and the table is full.

.Sh ERRORS

The

.Fn hcreate

and

.Fn hsearch

functions may fail if:

.Bl -tag -width Er

.It Bq Er ENOMEM

Insufficient storage space is available.

.El

.Sh 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.

.Bd -literal

#include 

#include 

#include 

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\en",

                            found_item->key,

                            ((struct info *)found_item->data)->age,

                            ((struct info *)found_item->data)->room);

                } else

                        (void)printf("no such employee %s\en", name_to_find);

        }

        return 0;

}

.Ed

.Sh SEE ALSO

.Xr bsearch 3 ,

.Xr lsearch 3 ,

.Xr malloc 3 ,

.Xr strcmp 3 ,

.Xr tsearch 3

.Sh STANDARDS

The

.Fn hcreate ,

.Fn hdestroy ,

and

.Fn hsearch

functions conform to

.St -xpg4.2 .

.Sh HISTORY

The

.Fn hcreate ,

.Fn hdestroy ,

and

.Fn hsearch

functions first appeared in

.At V .

.Sh BUGS

The interface permits the use of only one hash table at a time.