MBLEN(3)

NAME
mblen - get number of bytes in a multibyte character

SYNOPSIS
#include <stdlib.h>
int
mblen(const char *s, size_t n);

DESCRIPTION
The mblen() 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.

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 internal conversion state of the mblen() function, and are treated as if they were 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:

    mbtowc(NULL, s, n);

Calling any other function in libc never changes the internal state of mblen(), except for calling setlocale(3) with an LC_CTYPE that differs from the current locale. Such setlocale(3) calls cause the internal state of this function to become indeterminate.

The behaviour of mblen() is affected by the LC_CTYPE category of the current locale.

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.

RETURN VALUES
The mblen() function returns:

0   s points to a NUL byte (‘\0’).

positive
    The value returned is the number of bytes in 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 to an invalid or incomplete multibyte character. The mblen() function 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.

ERRORS
The mblen() function may cause an error in the following case:

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

SEE ALSO
mbrlen(3), mbtowc(3), setlocale(3)

STANDARDS
The mblen() function conforms to ansiC.