mblen - determine number of bytes in next multibyte character
s is not NULL, 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 known only 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.
n bytes starting at
s do not contain a complete multibyte character, mblen() returns -1. This can happen even if
n is greater than or equal to
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.
s is NULL, the mblen() function resets the shift state, known to only this function, to the initial state, and returns nonzero if the encoding has nontrivial shift state, or zero if the encoding is stateless.
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.
POSIX.1-2001, POSIX.1-2008, C99.
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