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mblen - determine number of bytes in next multibyte character
int mblen (const char *s, size_t n);
If s is not a NULL pointer, the mblen function inspects at most n bytes
of the multibyte string starting at s and extracts the next complete
multibyte character. It uses a static anonymous shift state only known
to the mblen function. 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 returns 0.
If the n bytes starting at s do not contain a complete multibyte
character, mblen returns -1. 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, mblen also returns -1.
If s is a NULL pointer, the mblen function resets the shift state, only
known to this function, to the initial state, and returns non-zero if
the encoding has non-trivial shift state, or zero if the encoding is
The mblen 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 -1, if an invalid multibyte sequence was encountered or if it
couldn't parse a complete multibyte character.
ISO/ANSI C, UNIX98
The behaviour of mblen depends on the LC_CTYPE category of the current
The function mbrlen provides a better interface to the same