converts a multibyte character to a
wide character (restartable)
* restrict wc, const char
* restrict s, size_t
n, mbstate_t * restrict
function examines at most n bytes of the multibyte
character byte string pointed to by s, converts those
bytes to a wide character, and stores the wide character in the wchar_t
object pointed to by wc if wc is
NULL and s points to a
Conversion happens in accordance with the
conversion state described by the mbstate_t object pointed to by
mbs. The mbstate_t object must be initialized to zero
before the application's first call to
If the previous call to
mbrtowc() did not return
(size_t)-1, the mbstate_t object can safely be reused without
The behaviour of
is affected by the
LC_CTYPE category of the current
locale. If the locale is changed without reinitialization of the mbstate_t
object pointed to by mbs, the behaviour of
mbrtowc() is undefined.
will accept an incomplete byte sequence pointed to by
s which does not form a complete character but is
potentially part of a valid character. In this case,
mbrtowc() consumes all such bytes. The conversion
state saved in the mbstate_t object pointed to by mbs
will be used to restart the suspended conversion during the next call to
In state-dependent encodings,
s may point to a special sequence of bytes called a
“shift sequence”. Shift sequences switch between character
code sets available within an encoding scheme. One encoding scheme using
shift sequences is ISO/IEC 2022-JP, which can switch e.g. from ASCII (which
uses one byte per character) to JIS X 0208 (which uses two bytes per
character). Shift sequence bytes correspond to no individual wide character,
treats them as if they were part of the subsequent multibyte character.
Therefore they do contribute to the number of bytes in the multibyte
Special cases in interpretation of arguments are as follows:
- wc == NULL
- The conversion from a multibyte character to a wide character is performed
and the conversion state may be affected, but the resulting wide character
This can be used to find out how many bytes are contained in the multibyte character pointed to by s.
- s == NULL
mbrtowc() ignores wc and n, and behaves equivalent to
mbrtowc(NULL, "", 1, mbs);
which attempts to use the mbstate_t object pointed to by mbs to start or continue conversion using the empty string as input, and discards the conversion result.
If conversion succeeds, this call always returns zero. Unlike mbtowc(3), the value returned does not indicate whether the current encoding of the locale is state-dependent, i.e. uses shift sequences.
- mbs == NULL
mbrtowc() uses its own internal state object to keep the conversion state, instead of an mbstate_t object pointed to by mbs. This internal conversion state is initialized once at program startup. It is not safe to call
mbrtowc() again with a
NULLmbs argument if
mbrtowc() returned (size_t)-1 because at this point the internal conversion state is undefined.
Calling any other functions in libc never changes the internal conversion state object of
- The bytes pointed to by s form a terminating NUL
character. If wc is not
NULL, a NUL wide character has been stored in the wchar_t object pointed to by wc.
- s points to a valid character, and the value
returned is the number of bytes completing the character. If
wc is not
NULL, the corresponding wide character has been stored in the wchar_t object pointed to by wc.
- s points to an illegal byte sequence which does not
form a valid multibyte character in the current locale.
mbrtowc() sets errno to EILSEQ. The conversion state object pointed to by mbs is left in an undefined state and must be reinitialized before being used again.
Because applications using
mbrtowc() are shielded from the specifics of the multibyte character encoding scheme, it is impossible to repair byte sequences containing encoding errors. Such byte sequences must be treated as invalid and potentially malicious input. Applications must stop processing the byte string pointed to by s and either discard any wide characters already converted, or cope with truncated input.
- s points to an incomplete byte sequence of length
n which has been consumed and contains part of a
valid multibyte character. The character may be completed by calling
mbrtowc() again with s pointing to one or more subsequent bytes of the multibyte character and mbs pointing to the conversion state object used during conversion of the incomplete byte sequence.
mbrtowc() function may cause an error
in the following cases:
- s points to an invalid multibyte character.
- mbs points to an invalid or uninitialized mbstate_t object.
mbrlen(3), mbtowc(3), setlocale(3)
mbrtowc() function conforms to ISO/IEC
9899/AMD1:1995 (“ISO C90, Amendment 1”). The restrict
qualifier is added at ISO/IEC 9899:1999 (“ISO C99”).
mbrtowc() is not suitable for programs
that care about internals of the character encoding scheme used by the byte
string pointed to by s.
It is possible that
because of locale configuration errors. An “invalid” character
sequence may simply be encoded in a different encoding than that of the
The special cases for s == NULL and
mbs == NULL do not make any sense. Instead of passing
NULL for mbs,
mbtowc(3) can be used.
Earlier versions of this man page implied that calling
mbrtowc() with a
s argument would always set mbs
to the initial conversion state. But this is true only if the previous call
mbrtowc() using mbs did not
return (size_t)-1 or (size_t)-2. It is recommended to zero the mbstate_t