143 lines
4.9 KiB
Groff
143 lines
4.9 KiB
Groff
.\" Copyright (c) 2002-2004 Tim J. Robbins. All rights reserved.
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.\" 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. 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 September 9, 2019
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.Dt MULTIBYTE 3
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.Os
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.Sh NAME
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.Nm multibyte
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.Nd multibyte and wide character manipulation functions
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In limits.h
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.In stdlib.h
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.In wchar.h
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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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.Vt 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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wide characters and
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multibyte 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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.Vt 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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.Vt char Ns s .
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Individual basic elements may map into one or more
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(up to
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.Dv MB_LEN_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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.Vt 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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Some functions (e.g.,
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.Xr mblen 3 ,
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.Xr mbtowc 3
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and
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.Xr wctomb 3 )
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maintain static shift state internally, whereas
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others store it in an
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.Vt mbstate_t
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object passed by the caller.
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Shift states are undefined after a call to
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.Xr setlocale 3
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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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(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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(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 C library provides the following functions for dealing with
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multibyte characters:
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.Bl -column "Description"
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.It Sy "Function Description"
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.It Xr mblen 3 Ta "get number of bytes in a character"
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.It Xr mbrlen 3 Ta "get number of bytes in a character (restartable)"
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.It Xr mbrtowc 3 Ta "convert a character to a wide-character code (restartable)"
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.It Xr mbsrtowcs 3 Ta "convert a character string to a wide-character string (restartable)"
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.It Xr mbstowcs 3 Ta "convert a character string to a wide-character string"
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.It Xr mbtowc 3 Ta "convert a character to a wide-character code"
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.It Xr wcrtomb 3 Ta "convert a wide-character code to a character (restartable)"
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.It Xr wcstombs 3 Ta "convert a wide-character string to a character string"
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.It Xr wcsrtombs 3 Ta "convert a wide-character string to a character string (restartable)"
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.It Xr wctomb 3 Ta "convert a wide-character code to a character"
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.El
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.Sh SEE ALSO
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.Xr localedef 1 ,
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.Xr setlocale 3 ,
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.Xr stdio 3 ,
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.Xr big5 5 ,
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.Xr euc 5 ,
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.Xr gb18030 5 ,
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.Xr gb2312 5 ,
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.Xr gbk 5 ,
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.Xr mskanji 5 ,
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.Xr utf8 5
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.Sh STANDARDS
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These functions conform to
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.St -isoC-99 .
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