| MULTIBYTE(3) | Library Functions Manual | MULTIBYTE(3) |
multibyte —
multibyte and wide character manipulation
functions
Standard C Library (libc, -lc)
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_LEN_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. Some functions
(e.g., mblen(3),
mbtowc(3) and
wctomb(3)) maintain static shift state
internally, whereas others store it in an mbstate_t
object passed by the caller. Shift states are undefined after a call to
setlocale(3) 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 C library provides the following functions for dealing with multibyte characters:
| Function | Description |
| mblen(3) | get number of bytes in a character |
| mbrlen(3) | get number of bytes in a character (restartable) |
| mbrtowc(3) | convert a character to a wide-character code (restartable) |
| mbsrtowcs(3) | convert a character string to a wide-character string (restartable) |
| mbstowcs(3) | convert a character string to a wide-character string |
| mbtowc(3) | convert a character to a wide-character code |
| wcrtomb(3) | convert a wide-character code to a character (restartable) |
| wcstombs(3) | convert a wide-character string to a character string |
| wcsrtombs(3) | convert a wide-character string to a character string (restartable) |
| wctomb(3) | convert a wide-character code to a character |
mklocale(1), setlocale(3), stdio(3), big5(5), euc(5), gb18030(5), gb2312(5), gbk(5), mskanji(5), utf8(5)
These functions conform to ISO/IEC 9899:1999 (“ISO C99”).
| April 8, 2004 | macOS 15.0 |