MBLEN(3) Linux Programmer's Manual MBLEN(3)
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
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.
GNU 1999-07-25 MBLEN(3)