|MBRTOWC(3)||Library Functions Manual||MBRTOWC(3)|
mbrtowc — converts
a multibyte character to a wide character (restartable)
* restrict wc, const char
* restrict s, size_t
n, mbstate_t * restrict
mbrtowc() 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 not
NULL and s points to a valid
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
mbrtowc(). If the previous call to
mbrtowc() did not return (size_t)-1, the mbstate_t
object can safely be reused without reinitialization.
The behaviour of
mbrtowc() is affected by
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.
mbrtowc() 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, so
mbrtowc() treats them
as if they were part of the subsequent multibyte character. Therefore they
do contribute to the number of bytes in the multibyte character.
Special cases in interpretation of arguments are as follows:
This can be used to find out how many bytes are contained in the multibyte character pointed to by s.
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.
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
NULL, a NUL wide character has been stored in the wchar_t object pointed to by wc.
NULL, the corresponding wide character has been stored in the wchar_t object pointed to by wc.
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
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.
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:
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
|February 8, 2016||OpenBSD-current|