multibyte.3

早期freebsd实现

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.\"	@(#)multibyte.3	8.1 (Berkeley) 6/4/93
.\"
.Dd "June 4, 1993"
.Dt MULTIBYTE 3
.Os
.Sh NAME
.Nm mblen ,
.Nm mbstowcs ,
.Nm mbtowc ,
.Nm wcstombs ,
.Nm wctomb
.Nd multibyte character support for C
.Sh SYNOPSIS
.Fd #include <stdlib.h>
.Ft int
.Fn mblen "const char *mbchar" "int nbytes"
.Ft size_t
.Fn mbstowcs "wchar_t *wcstring" "const char *mbstring" "size_t nwchars"
.Ft int
.Fn mbtowc "wchar_t *wcharp" "const char *mbchar" "size_t nbytes"
.Ft size_t
.Fn wcstombs "char *mbstring" "const wchar_t *wcstring" "size_t nbytes"
.Ft int
.Fn wctomb "char *mbchar" "wchar_t wchar"
.Sh DESCRIPTION
The basic elements of some written natural languages such as Chinese
cannot be represented uniquely with single C
.Va char Ns s .
The C standard supports two different ways of dealing with
extended natural language encodings,
.Em wide
characters and
.Em multibyte
characters.
Wide characters are an internal representation
which allows each basic element to map
to a single object of type
.Va wchar_t .
Multibyte characters are used for input and output
and code each basic element as a sequence of C
.Va char Ns s .
Individual basic elements may map into one or more
.Pq up to Dv MB_CHAR_MAX
bytes in a multibyte character.
.Pp
The current locale
.Pq Xr setlocale 3
governs the interpretation of wide and multibyte characters.
The locale category
.Dv LC_CTYPE
specifically controls this interpretation.
The
.Va wchar_t
type is wide enough to hold the largest value
in the wide character representations for all locales.
.Pp
Multibyte strings may contain
.Sq shift
indicators to switch to and from
particular modes within the given representation.
If explicit bytes are used to signal shifting,
these are not recognized as separate characters
but are lumped with a neighboring character.
There is always a distinguished
.Sq initial
shift state.
The
.Fn mbstowcs
and
.Fn wcstombs
functions assume that multibyte strings are interpreted
starting from the initial shift state.
The
.Fn mblen ,
.Fn mbtowc
and
.Fn wctomb
functions maintain static shift state internally.
A call with a null
.Fa mbchar
pointer returns nonzero if the current locale requires shift states,
zero otherwise;
if shift states are required, the shift state is reset to the initial state.
The internal shift states are undefined after a call to
.Fn setlocale
with the
.Dv LC_CTYPE
or
.Dv LC_ALL
categories.
.Pp
For convenience in processing,
the wide character with value 0
.Pq the null wide character
is recognized as the wide character string terminator,
and the character with value 0
.Pq the null byte
is recognized as the multibyte character string terminator.
Null bytes are not permitted within multibyte characters.
.Pp
The
.Fn mblen
function computes the length in bytes
of a multibyte character
.Fa mbchar .
Up to
.Fa nbytes
bytes are examined.
.Pp
The
.Fn mbtowc
function converts a multibyte character
.Fa mbchar
into a wide character and stores the result
in the object pointed to by
.Fa wcharp.
Up to
.Fa nbytes
bytes are examined.
.Pp
The
.Fn wctomb
function converts a wide character
.Fa wchar
into a multibyte character and stores
the result in
.Fa mbchar .
The object pointed to by
.Fa mbchar
must be large enough to accommodate the multibyte character.  
.Pp
The
.Fn mbstowcs
function converts a multibyte character string
.Fa mbstring
into a wide character string
.Fa wcstring .
No more than
.Fa nwchars
wide characters are stored.
A terminating null wide character is appended if there is room.
.Pp
The
.Fn wcstombs
function converts a wide character string
.Fa wcstring
into a multibyte character string
.Fa mbstring .
Up to
.Fa nbytes
bytes are stored in
.Fa mbstring .
Partial multibyte characters at the end of the string are not stored.
The multibyte character string is null terminated if there is room.
.Sh "RETURN VALUES
If multibyte characters are not supported in the current locale,
all of these functions will return \-1 if characters can be processed,
otherwise 0.
.Pp
If
.Fa mbchar
is
.Dv NULL ,
the
.Fn mblen ,
.Fn mbtowc
and
.Fn wctomb
functions return nonzero if shift states are supported,
zero otherwise.
If
.Fa mbchar
is valid,
then these functions return
the number of bytes processed in
.Fa mbchar ,
or \-1 if no multibyte character
could be recognized or converted.
.Pp
The
.Fn mbstowcs
function returns the number of wide characters converted,
not counting any terminating null wide character.
The
.Fn wcstombs
function returns the number of bytes converted,
not counting any terminating null byte.
If any invalid multibyte characters are encountered,
both functions return \-1.
.Sh "SEE ALSO
.Xr euc 4 ,
.Xr mbrune 3 ,
.Xr rune 3 ,
.Xr setlocale 3 ,
.Xr utf2 4
.Sh STANDARDS
The
.Fn mblen ,
.Fn mbstowcs ,
.Fn mbtowc ,
.Fn wcstombs
and
.Fn wctomb
functions conform to
.St -ansiC .
.Sh BUGS
The current implementation does not support shift states.