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mbrtowc - convert a multibyte sequence to a wide character
size_t mbrtowc(wchar_t *pwc, const char *s, size_t n, mbstate_t *ps);
The main case for this function is when s is not NULL and pwc is not
NULL. In this case, the mbrtowc() function inspects at most n bytes of
the multibyte string starting at s, extracts the next complete
multibyte character, converts it to a wide character and stores it at
*pwc. It updates the shift state *ps. If the converted wide character
is not L’\0’, it returns the number of bytes that were consumed from s.
If the converted wide character is L’\0’, it resets the shift state *ps
to the initial state and returns 0.
If the n bytes starting at s do not contain a complete multibyte
character, mbrtowc() returns (size_t) -2. This can happen even if n >=
MB_CUR_MAX, if the multibyte string contains redundant shift sequences.
If the multibyte string starting at s contains an invalid multibyte
sequence before the next complete character, mbrtowc() returns
(size_t) -1 and sets errno to EILSEQ. In this case, the effects on *ps
A different case is when s is not NULL but pwc is NULL. In this case
the mbrtowc() function behaves as above, except that it does not store
the converted wide character in memory.
A third case is when s is NULL. In this case, pwc and n are ignored.
If the conversion state represented by *ps denotes an incomplete
multibyte character conversion, the mbrtowc() function returns
(size_t) -1, sets errno to EILSEQ, and leaves *ps in an undefined
state. Otherwise, the mbrtowc() function puts *ps in the initial state
and returns 0.
In all of the above cases, if ps is a NULL pointer, a static anonymous
state only known to the mbrtowc function is used instead. Otherwise,
*ps must be a valid mbstate_t object. An mbstate_t object a can be
initialized to the initial state by zeroing it, for example using
memset(&a, 0, sizeof(a));
The mbrtowc() function returns the number of bytes parsed from the
multibyte sequence starting at s, if a non-L’\0’ wide character was
recognized. It returns 0, if a L’\0’ wide character was recognized.
It returns (size_t) -1 and sets errno to EILSEQ, if an invalid
multibyte sequence was encountered. It returns (size_t) -2 if it
couldn’t parse a complete multibyte character, meaning that n should be
The behavior of mbrtowc() depends on the LC_CTYPE category of the
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