MULTIBYTE(3)

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 to MB_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
euc(4), mbrune(3), rune(3), setlocale(3), utf2(4)

STANDARDS
The mblen(), mbstowcs(), mbtowc(), wcstombs() and wctomb() functions conform to ansiC.

BUGS
The current implementation does not support shift states.