b6cbf7203b
This patch imports the unmodified current version of NetBSD libc. The NetBSD includes are in /nbsd_include, while the libc code itself is split between lib/nbsd_libc and common/lib/libc.
241 lines
5.3 KiB
Groff
241 lines
5.3 KiB
Groff
.\" $NetBSD: hcreate.3,v 1.8 2010/05/01 06:18:03 jruoho Exp $
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.\"
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.\" Copyright (c) 1999 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Klaus Klein.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd May 1, 2010
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.Dt HCREATE 3
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.Os
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.Sh NAME
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.Nm hcreate ,
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.Nm hdestroy ,
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.Nm hsearch
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.Nd manage hash search table
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In search.h
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.Ft int
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.Fn hcreate "size_t nel"
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.Ft void
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.Fn hdestroy "void"
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.Ft ENTRY *
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.Fn hsearch "ENTRY item" "ACTION action"
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.Sh DESCRIPTION
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The
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.Fn hcreate ,
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.Fn hdestroy
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and
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.Fn hsearch
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functions manage hash search tables.
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.Pp
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The
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.Fn hcreate
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function allocates and initializes the table.
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The
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.Fa nel
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argument specifies an estimate of the maximum number of entries to be held
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by the table.
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Unless further memory allocation fails, supplying an insufficient
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.Fa nel
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value will not result in functional harm, although a performance degradation
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may occur.
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Initialization using the
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.Fn hcreate
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function is mandatory prior to any access operations using
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.Fn hsearch .
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.Pp
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The
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.Fn hdestroy
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function destroys a table previously created using
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.Fn hcreate .
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After a call to
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.Fn hdestroy ,
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the data can no longer be accessed.
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.Pp
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The
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.Fn hsearch
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function is used to search to the hash table.
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It returns a pointer into the
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hash table indicating the address of an item.
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The
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.Fa item
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argument is of type
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.Vt ENTRY ,
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defined in the
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.In search.h
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header.
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This is a structure type that contains two pointers:
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.Pp
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.Bl -tag -compact -offset indent -width "void *data "
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.It Fa char *key
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comparison key
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.It Fa void *data
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pointer to data associated with
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.Fa key
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.El
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.Pp
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The key comparison function used by
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.Fn hsearch
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is
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.Xr strcmp 3 .
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.Pp
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The
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.Fa action
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argument is of type
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.Vt ACTION ,
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an enumeration type which defines the following values:
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.Bl -tag -offset indent -width ENTERXX
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.It Dv ENTER
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Insert
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.Fa item
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into the hash table.
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If an existing item with the same key is found, it is not replaced.
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Note that the
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.Fa key
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and
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.Fa data
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elements of
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.Fa item
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are used directly by the new table entry.
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The storage for the
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key must not be modified during the lifetime of the hash table.
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.It Dv FIND
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Search the hash table without inserting
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.Fa item .
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.El
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.Pp
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Note that the comparison
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.Fa key
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must be allocated using
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.Xr malloc 3
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or
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.Xr calloc 3
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if action is
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.Dv ENTER
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and
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.Fn hdestroy
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will be called.
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This is because
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.Fn hdestroy
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will call
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.Xr free 3
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for each comparison
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.Fa key
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(but not
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.Fa data ) .
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Typically the comparison
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.Fa key
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is allocated by using
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.Xr strdup 3 .
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.Sh RETURN VALUES
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If successful, the
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.Fn hcreate
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function returns a non-zero value.
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Otherwise, a value of 0 is returned and
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.Va errno
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is set to indicate the error.
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.Pp
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The
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.Fn hdestroy
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functions
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returns no value.
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.Pp
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If successful, the
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.Fn hsearch
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function returns a pointer to hash table entry matching
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the provided key.
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If the action is
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.Dv FIND
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and the item was not found, or if the action is
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.Dv ENTER
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and the insertion failed,
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.Dv NULL
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is returned and
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.Va errno
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is set to indicate the error.
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If the action is
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.Dv ENTER
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and an entry already existed in the table matching the given
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key, the existing entry is returned and is not replaced.
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.Sh ERRORS
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The
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.Fn hcreate
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and
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.Fn hsearch
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functions will fail if:
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.Bl -tag -width Er
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.It Bq Er ENOMEM
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Insufficient memory is available.
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.El
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.Sh SEE ALSO
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.Xr bsearch 3 ,
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.Xr lsearch 3 ,
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.Xr malloc 3 ,
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.Xr strcmp 3
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.Sh STANDARDS
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The
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.Fn hcreate ,
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.Fn hdestroy
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and
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.Fn hsearch
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functions conform to
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.St -xpg4.2 .
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.Sh HISTORY
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The
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.Fn hcreate ,
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.Fn hdestroy
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and
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.Fn hsearch
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functions first appeared in
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.At V .
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.Sh CAVEATS
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At least the following limitations can be mentioned:
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.Bl -bullet
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.It
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The interface permits the use of only one hash table at a time.
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.It
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Individual hash table entries can be added, but not deleted.
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.It
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The standard is indecipherable about the
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internal memory usage of the functions,
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mentioning only that
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.Do
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.Fn hcreate
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and
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.Fn hsearch
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functions may use
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.Fn malloc
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to allocate space
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.Dc .
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This limits the portability of the functions,
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given that other implementations may not
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.Xr free 3
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the buffer pointed by
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.Fa key .
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.El
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