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MBLEN(3) Library Functions Manual MBLEN(3)

mblen — get number of bytes in a multibyte character

#include <stdlib.h>

int
mblen(const char *s, size_t n);

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.

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 never change the internal state of the (), 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 () is affected by the LC_CTYPE category of the current locale.

There are special cases:

s == NULL
() 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.

Normally, mblen() 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 when this value is greater than n or the value of the MB_CUR_MAX macro.
-1
s points an invalid or incomplete multibyte character. The mblen() also sets errno to indicate the error.

When s is equal to NULL, mblen() returns:

0
The current encoding is state-independent.
non-zero
The current encoding is state-dependent.

The mblen() may causes an error in the following case:

[]
s points to an invalid or incomplete multibyte character.

mbrlen(3), mbtowc(3), setlocale(3)

The mblen() function conforms to ANSI X3.159-1989 (“ANSI C89”).

June 5, 2013 OpenBSD-7.0