mbrlen - determine number of bytes in next multibyte character
s, size_t n, mbstate_t *ps);
The mbrlen function inspects at most n bytes
of the multibyte string starting at s and extracts
the next complete multibyte character. It updates the shift
state *ps. If the multibyte character is not the null
wide character, it returns the number of bytes that were
consumed from s. If the multibyte character is the
null wide character, 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, mbrlen 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, mbrlen returns (size_t)(-1) and
sets errno to EILSEQ. In this case, the
effects on *ps are undefined.
If ps is a NULL pointer, a static anonymous state
only known to the mbrlen function is used
The mbrlen function returns the number of bytes
parsed from the multibyte sequence starting at s, if
a non-null wide character was recognized. It returns 0, if a
null 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 increased.
ISO/ANSI C, UNIX98
The behaviour of mbrlen depends on the LC_CTYPE
category of the current locale.