mbrtowc.3c (2010 09)

m
mbrtowc(3C) mbrtowc(3C)
NAME
mbrtowc( ) - convert a character to a wide-character code (restartable)
SYNOPSIS
#include <wchar.h>
size_t mbrtowc(wchar_t *__restrict pwc, const char *__restrict s, size_t
n, mbstate_t *__restrict ps);
DESCRIPTION
If s is a null pointer, the
mbrtowc() function is equivalent to the call:
mbrtowc(NULL, "", 1, ps)
In this case, the values of the arguments pwc and n are ignored.
If s is not a null pointer, the
mbrtowc() function inspects at most n bytes beginning at the byte pointed
to by s to determine the number of bytes needed to complete the next character (including any shift
sequences). If the function determines that the next character is completed, it determines the value of
the corresponding wide-character and then, if pwc is not a null pointer, stores that value in the object
pointed to by pwc . If the corresponding wide-character is the null wide-character, the resulting state
described is the initial conversion state.
If ps is a null pointer, the
mbrtowc() function uses its own internal mbstate_t object, which is initial-
ized at program startup to the initial conversion state. Otherwise, the mbstate_t object pointed to by ps is
used to completely describe the current conversion state of the associated character sequence.
APPLICATION USAGE
The prototype of this function is available to applications if they are:
a.
c99 conformant.
b. Compiled with
-D_XOPEN_SOURCE
macro with a value >=500.
c. Compiled with
-D_POSIX_C_SOURCE
macro with a value >= 200112.
EXTERNAL INFLUENCES
Environment Variables
The behavior of this function is affected by the
LC_CTYPE category of the current locale.
RETURN VALUE
The
mbrtowc() function returns the first of the following that applies:
0 If the next n or fewer bytes complete the character that corresponds to the null wide-
character (which is the value stored).
Positive If the next n or fewer bytes complete a valid character (which is the value stored); the
value returned is the number of bytes that complete the character.
(size_t )-2 If the next n bytes contribute to an incomplete but potentially valid character, and all n
bytes have been processed (no value is stored). When n has at least the value of the
MB_CUR_MAX macro, this case can only occur if s points at a sequence of redundant
shift sequences (for implementations with state-dependent encodings).
(size_t )-1 If an encoding error occurs, in which case the next n or fewer bytes do not contribute to
a complete and valid character (no value is stored). In this case, [EILSEQ] is stored in
errno and the conversion state is undefined.
ERRORS
The
mbrtowc() function may fail if:
[EILSEQ] Invalid character sequence is detected.
[EINVAL] ps points to an object that contains an invalid conversion state.
WARNINGS
With the exception of ASCII characters, the code values of wide characters (type of
wchar_t) are specific
to the effective locale specified by the LC_CTYPE environment variable. These values may not be compa-
tible with values obtained by specifying other locales that are supported now, or which may be supported
in the future. It is recommended that wide character constants and wide string literals (see the C
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