MBRLEN(3) Library Functions Manual MBRLEN(3)

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

Standard C Library (libc, -lc)

#include <wchar.h>

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

#include <wchar.h>
#include <xlocale.h>

size_t
mbrlen_l(const char *restrict s, size_t n, mbstate_t *restrict ps, locale_t loc);

The () function inspects at most n bytes, pointed to by s, to determine the number of bytes needed to complete the next multibyte character.

The mbstate_t argument, ps, is used to keep track of the shift state. If it is NULL, () uses an internal, static mbstate_t object, which is initialized to the initial conversion state at program startup.

It is equivalent to:

mbrtowc(NULL, s, n, ps);

Except that, when ps is a NULL pointer, () uses its own static, internal mbstate_t object to keep track of the shift state.

Although the () function uses the current locale, the () function may be passed a locale directly. See xlocale(3) for more information.

The mbrlen() functions returns:

0
The next n or fewer bytes represent the null wide character (L'\0').
>0
The next n or fewer bytes represent a valid character, mbrlen() returns the number of bytes used to complete the multibyte character.
(size_t)-2
The next n contribute to, but do not complete, a valid multibyte character sequence, and all n bytes have been processed.
(size_t)-1
An encoding error has occurred. The next n or fewer bytes do not contribute to a valid multibyte character.

A function that calculates the number of characters in a multibyte character string:

size_t
nchars(const char *s)
{
	size_t charlen, chars;
	mbstate_t mbs;

	chars = 0;
	memset(&mbs, 0, sizeof(mbs));
	while ((charlen = mbrlen(s, MB_CUR_MAX, &mbs)) != 0 &&
	    charlen != (size_t)-1 && charlen != (size_t)-2) {
		s += charlen;
		chars++;
	}

	return (chars);
}

The mbrlen() function will fail if:

[]
An invalid multibyte sequence was detected.
[]
The conversion state is invalid.

mblen(3), mbrtowc(3), multibyte(3), xlocale(3)

The mbrlen() function conforms to ISO/IEC 9899:1999 (“ISO C99”).

April 7, 2004 macOS 15.2