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MBRLEN(3) Library Functions Manual MBRLEN(3)

mbrlen — get number of bytes in a multibyte character (restartable)

#include <wchar.h>

size_t
mbrlen(const char * restrict s, size_t n, mbstate_t * restrict ps);

The () 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.

() is equivalent to the following call (except ps is evaluated only once):

mbrtowc(NULL, s, n, (ps != NULL) ? ps : &internal);

Here, internal is an internal state object.

In state-dependent encodings, s may point to the special sequence bytes to change the shift-state. Although such sequence bytes corresponds to no individual wide-character code, these affect the conversion state object pointed to by ps, and the () treats the special sequence bytes as if these are a part of the subsequent multibyte character.

Unlike mblen(3), () may accept the byte sequence when it is not a complete character but possibly contains part of a valid character. In this case, this function will accept all such bytes and save 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 the () is affected by LC_CTYPE category of the current locale.

There are the special cases:

s == NULL
() sets the conversion state object pointed to by ps to an initial 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, () ignores n.

n == 0
In this case, the first n bytes of the array pointed to by 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 ps mentioned in this manual page.

Calling any other functions in never change the internal state of (), except for calling setlocale(3) with a changing LC_CTYPE category of the current locale. Such setlocale(3) calls cause the internal state of this function to be indeterminate. This internal state is initialized at startup time of the program.

The mbrlen() returns:

0
s points to a null byte (‘\0’).
positive
The value returned is a number of bytes for the valid multibyte character pointed to by s. There are no cases where this value is greater than n or the value of the MB_CUR_MAX macro.
(size_t)-2
s points to the byte sequence which possibly contains part of a valid multibyte character, but which is incomplete. When n is at least MB_CUR_MAX can only occur if the array pointed to by s contains a redundant shift sequence.
(size_t)-1
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 following cases:

[]
s points to an invalid multibyte character.
[]
ps points to an invalid or uninitialized mbstate_t object.

mblen(3), mbrtowc(3), setlocale(3)

The 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”).

June 5, 2013 OpenBSD-6.6