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mblen - determine number of bytes in next multibyte character
#include <stdlib.h> 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 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.
ISO/ANSI C, UNIX98
The behaviour of mblen depends on the LC_CTYPE category of the current locale. The function mbrlen provides a better interface to the same functionality.