The
mblen() function usually determines the number of bytes in a multibyte character pointed to by
s and returns it. This function shall only examine max n bytes of the array beginning from
s.
In state-dependent encodings,
s may point the special sequence bytes to change the shift-state. Although such sequence bytes corresponds to no individual wide-character code, the
mblen() changes the own state by them and treats them as if they are a part of the subsequent multibyte character.
Unlike
mbrlen(3), the first
n bytes pointed to by
s need to form an entire multibyte character. Otherwise, this function causes an error.
mblen() is equivalent to the following call, except the internal state of the
mbtowc(3) function is not affected:
Calling any other functions in
Standard C Library (libc, -lc) never changes the internal state of
mblen(), except for calling
setlocale(3) with the
LC_CTYPE category changed to that of the current locale. Such
setlocale(3) calls cause the internal state of this function to be indeterminate.
The behaviour of
mblen() is affected by the
LC_CTYPE category of the current locale.
These are the special cases:
s == NULL
mblen() initializes its own internal state to an initial state, and determines whether the current encoding is state-dependent. This function returns 0 if the encoding is state-independent, otherwise non-zero.
n == 0
In this case, the first n bytes of the array pointed to by s never form a complete character. Thus, mblen() always fails.