The basic elements of some written natural languages, such as Chinese,
cannot be represented uniquely with single C
Vt char Ns s .
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
Vt wchar_t .
Multibyte characters are used for input and output
and code each basic element as a sequence of C
Vt char Ns s .
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
Vt 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
Vt 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:
