245 lines
6.7 KiB
Groff
245 lines
6.7 KiB
Groff
.\" Copyright (c) 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Donn Seeley of BSDI.
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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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)multibyte.3 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd June 4, 1993
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.Dt MULTIBYTE 3
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.Os
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.Sh NAME
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.Nm mblen ,
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.Nm mbstowcs ,
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.Nm mbtowc ,
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.Nm wcstombs ,
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.Nm wctomb
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.Nd multibyte character support for C
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.Fd #include <stdlib.h>
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.Ft int
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.Fn mblen "const char *mbchar" "size_t nbytes"
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.Ft size_t
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.Fn mbstowcs "wchar_t *wcstring" "const char *mbstring" "size_t nwchars"
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.Ft int
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.Fn mbtowc "wchar_t *wcharp" "const char *mbchar" "size_t nbytes"
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.Ft size_t
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.Fn wcstombs "char *mbstring" "const wchar_t *wcstring" "size_t nbytes"
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.Ft int
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.Fn wctomb "char *mbchar" "wchar_t wchar"
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.Sh DESCRIPTION
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The basic elements of some written natural languages such as Chinese
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cannot be represented uniquely with single C
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.Va char Ns s .
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The C standard supports two different ways of dealing with
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extended natural language encodings,
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.Em wide
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characters and
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.Em multibyte
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characters.
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Wide characters are an internal representation
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which allows each basic element to map
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to a single object of type
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.Va wchar_t .
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Multibyte characters are used for input and output
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and code each basic element as a sequence of C
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.Va char Ns s .
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Individual basic elements may map into one or more
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.Pq up to Dv MB_CHAR_MAX
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bytes in a multibyte character.
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.Pp
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The current locale
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.Pq Xr setlocale 3
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governs the interpretation of wide and multibyte characters.
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The locale category
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.Dv LC_CTYPE
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specifically controls this interpretation.
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The
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.Va wchar_t
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type is wide enough to hold the largest value
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in the wide character representations for all locales.
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.Pp
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Multibyte strings may contain
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.Sq shift
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indicators to switch to and from
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particular modes within the given representation.
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If explicit bytes are used to signal shifting,
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these are not recognized as separate characters
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but are lumped with a neighboring character.
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There is always a distinguished
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.Sq initial
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shift state.
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The
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.Fn mbstowcs
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and
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.Fn wcstombs
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functions assume that multibyte strings are interpreted
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starting from the initial shift state.
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The
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.Fn mblen ,
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.Fn mbtowc
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and
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.Fn wctomb
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functions maintain static shift state internally.
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A call with a null
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.Fa mbchar
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pointer returns nonzero if the current locale requires shift states,
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zero otherwise;
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if shift states are required, the shift state is reset to the initial state.
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The internal shift states are undefined after a call to
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.Fn setlocale
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with the
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.Dv LC_CTYPE
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or
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.Dv LC_ALL
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categories.
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.Pp
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For convenience in processing,
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the wide character with value 0
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.Pq the null wide character
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is recognized as the wide character string terminator,
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and the character with value 0
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.Pq the null byte
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is recognized as the multibyte character string terminator.
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Null bytes are not permitted within multibyte characters.
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.Pp
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The
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.Fn mblen
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function computes the length in bytes
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of a multibyte character
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.Fa mbchar .
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Up to
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.Fa nbytes
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bytes are examined.
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.Pp
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The
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.Fn mbtowc
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function converts a multibyte character
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.Fa mbchar
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into a wide character and stores the result
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in the object pointed to by
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.Fa wcharp .
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Up to
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.Fa nbytes
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bytes are examined.
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.Pp
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The
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.Fn wctomb
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function converts a wide character
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.Fa wchar
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into a multibyte character and stores
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the result in
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.Fa mbchar .
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The object pointed to by
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.Fa mbchar
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must be large enough to accommodate the multibyte character.
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.Pp
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The
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.Fn mbstowcs
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function converts a multibyte character string
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.Fa mbstring
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into a wide character string
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.Fa wcstring .
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No more than
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.Fa nwchars
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wide characters are stored.
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A terminating null wide character is appended if there is room.
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.Pp
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The
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.Fn wcstombs
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function converts a wide character string
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.Fa wcstring
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into a multibyte character string
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.Fa mbstring .
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Up to
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.Fa nbytes
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bytes are stored in
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.Fa mbstring .
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Partial multibyte characters at the end of the string are not stored.
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The multibyte character string is null terminated if there is room.
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.Sh "RETURN VALUES
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If multibyte characters are not supported in the current locale,
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all of these functions will return \-1 if characters can be processed,
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otherwise 0.
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.Pp
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If
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.Fa mbchar
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is
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.Dv NULL ,
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the
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.Fn mblen ,
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.Fn mbtowc
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and
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.Fn wctomb
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functions return nonzero if shift states are supported,
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zero otherwise.
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If
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.Fa mbchar
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is valid,
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then these functions return
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the number of bytes processed in
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.Fa mbchar ,
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or \-1 if no multibyte character
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could be recognized or converted.
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.Pp
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The
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.Fn mbstowcs
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function returns the number of wide characters converted,
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not counting any terminating null wide character.
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The
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.Fn wcstombs
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function returns the number of bytes converted,
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not counting any terminating null byte.
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If any invalid multibyte characters are encountered,
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both functions return \-1.
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.Sh "SEE ALSO
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.Xr mbrune 3 ,
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.Xr rune 3 ,
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.Xr setlocale 3 ,
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.Xr euc 4 ,
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.Xr utf2 4
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.Sh STANDARDS
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The
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.Fn mblen ,
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.Fn mbstowcs ,
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.Fn mbtowc ,
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.Fn wcstombs
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and
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.Fn wctomb
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functions conform to
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.St -ansiC .
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.Sh BUGS
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The current implementation does not support shift states.
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