get number of bytes in a multibyte
char * restrict s, size_t
n, mbstate_t * restrict
function returns the number of bytes in the first multibyte character of the
multibyte string s. It examines at most the first
n bytes of s.
is equivalent to the following call, except that ps is
evaluated only once:
mbrtowc(NULL, s, n, (ps != NULL) ? ps : &internal);
Here, internal is an internal state object automatically initialized to the initial conversion state at startup time of the program.
In state-dependent encodings,
s may point to special sequence bytes changing the
shift state. Although such sequence bytes correspond to no wide character,
they affect the conversion state object pointed to by
treats the special sequence bytes as if they were part of the subsequent
accepts the byte sequence if it is not a complete character but the initial
part of some valid character. In this case, this function accepts all such
bytes and saves them into the conversion state object pointed to by
ps. They will be used on subsequent calls of this
function to restart the conversion suspended.
The behaviour of
is affected by the
LC_CTYPE category of the current
There are the special cases:
- s == NULL
mbrlen() sets the conversion state object pointed to by ps to the initial conversion state and always returns 0. Unlike mblen(3), the value returned does not indicate whether the current encoding of the locale is state-dependent.
In this case,
mbrlen() ignores n.
- n == 0
- In this case, the first n bytes of
s never form a complete character. Thus,
mbrlen() always returns (size_t)-2.
- ps == NULL
mbrlen() uses its own internal state object to keep the conversion state instead of the ps argument.
Calling any other function in libc never changes the internal state of
mbrlen(), except for calling setlocale(3) with an
LC_CTYPEthat differs from the current locale. Such setlocale(3) calls cause the internal state of this function to become indeterminate.
mbrlen() function returns:
- s points to a NUL byte (‘\0’).
- The value returned is the number of bytes in the valid multibyte character
pointed to by s. There are no cases where this value
is greater than n or the value of the
- The first n bytes of s contain
an incomplete multibyte character that can potentially be completed by
reading more bytes. When n is at least
MB_CUR_MAX, this can only occur if s contains a redundant shift sequence.
- s points to an illegal byte sequence which does not
form a valid multibyte character. In this case,
mbrtowc() sets errno to indicate the error.
mbrlen() may cause an error in the
- s points to an invalid multibyte character.
- ps points to an invalid or uninitialized mbstate_t object.
mblen(3), mbrtowc(3), setlocale(3)
mbrlen() function conforms to ISO/IEC
9899/AMD1:1995 (“ISO C90, Amendment 1”). The restrict
qualifier is added at ISO/IEC 9899/1999 (“ISO C99”).