MBRTOWC(3) Linux Programmer's Manual MBRTOWC(3)
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 are undefined.
A different case is when s is not NULL but pwc is NULL. In this case the mbrtowc function
behaves as above, excepts 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
memset(&a, 0, sizeof(a));
The mbrtowc function returns the number of bytes parsed from the multibyte sequence start-
ing 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 com-
plete multibyte character, meaning that n should be increased.
ISO/ANSI C, UNIX98
The behaviour of mbrtowc depends on the LC_CTYPE category of the current locale.
GNU 2001-11-22 MBRTOWC(3)