get number of bytes in a multibyte
char *s, size_t
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
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
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.
is equivalent to the following call, except the internal state of the
mbtowc(3) function is not affected:
mbtowc(NULL, s, n);
Calling any other functions in
libc never change
the internal state of the
except for calling
setlocale(3) with the
changed to that of the current locale. Such
setlocale(3) calls cause the internal state of this function to be
The behaviour of
affected by the
LC_CTYPE category of the current
There are 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.
- s points to a null byte (‘\0’).
- The value returned is a number of bytes for the valid multibyte character
pointed to by s. There are no cases when this value
is greater than n or the value of the
- s points an invalid or incomplete multibyte
mblen() function also sets errno to indicate the error.
When s is equal to
- The current encoding is state-independent.
- The current encoding is state-dependent.
mblen() function may cause an error in
the following case:
- s points to an invalid or incomplete multibyte character.
mbrlen(3), mbtowc(3), setlocale(3)
mblen() function conforms to