NAME
mblen, mbstowcs,
mbtowc, wcstombs,
wctomb —
multibyte character support for
C
SYNOPSIS
#include
<stdlib.h>
int
mblen(const
char *mbchar, int
nbytes);
size_t
mbstowcs(wchar_t
*wcstring, const char
*mbstring, size_t
nwchars);
int
mbtowc(wchar_t
*wcharp, const char
*mbchar, size_t
nbytes);
size_t
wcstombs(char
*mbstring, const wchar_t
*wcstring, size_t
nbytes);
int
wctomb(char
*mbchar, wchar_t
wchar);
DESCRIPTION
The basic elements of some written natural languages such as Chinese cannot be represented uniquely with single C chars. The C standard supports two different ways of dealing with extended natural language encodings, wide characters and multibyte characters. Wide characters are an internal representation which allows each basic element to map to a single object of type wchar_t. Multibyte characters are used for input and output and code each basic element as a sequence of C chars. Individual basic elements may map into one or more (up toMB_CHAR_MAX) bytes in a
multibyte character.
The current locale
(setlocale(3)) governs the interpretation of wide and
multibyte characters. The locale category LC_CTYPE
specifically controls this interpretation. The wchar_t
type is wide enough to hold the largest value in the wide character
representations for all locales.
Multibyte strings may contain ‘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 ‘initial’ shift
state. The
mbstowcs()
and wcstombs() functions assume that multibyte
strings are interpreted starting from the initial shift state. The
mblen(), mbtowc() and
wctomb() functions maintain static shift state
internally. A call with a null 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
setlocale()
with the LC_CTYPE or LC_ALL
categories.
For convenience in processing, the wide character with value 0 (the null wide character) is recognized as the wide character string terminator, and the character with value 0 (the null byte) is recognized as the multibyte character string terminator. Null bytes are not permitted within multibyte characters.
The
mblen()
function computes the length in bytes of a multibyte character
mbchar. Up to nbytes bytes are
examined.
The
mbtowc()
function converts a multibyte character mbchar into a
wide character and stores the result in the object pointed to by
wcharp. Up to nbytes bytes are
examined.
The
wctomb()
function converts a wide character wchar into a
multibyte character and stores the result in mbchar.
The object pointed to by mbchar must be large enough
to accommodate the multibyte character.
The
mbstowcs()
function converts a multibyte character string
mbstring into a wide character string
wcstring. No more than nwchars
wide characters are stored. A terminating null wide character is appended if
there is room.
The
wcstombs()
function converts a wide character string wcstring
into a multibyte character string mbstring. Up to
nbytes bytes are stored in
mbstring. Partial multibyte characters at the end of
the string are not stored. The multibyte character string is null terminated
if there is room.
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.
If mbchar is NULL,
the mblen(), mbtowc() and
wctomb() functions return nonzero if shift states
are supported, zero otherwise. If mbchar is valid,
then these functions return the number of bytes processed in
mbchar, or -1 if no multibyte character could be
recognized or converted.
The mbstowcs() function returns the number
of wide characters converted, not counting any terminating null wide
character. The 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.
SEE ALSO
STANDARDS
The mblen(),
mbstowcs(), mbtowc(),
wcstombs() and wctomb()
functions conform to ANSI X3.159-1989
(“ANSI C89”).
BUGS
The current implementation does not support shift states.