.\" Copyright (c) 2002-2004 Tim J. Robbins
.\" All rights reserved.
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.\" $FreeBSD: src/lib/libc/locale/mbrlen.3,v 1.8 2004/06/30 19:32:41 ru Exp $
.\"
.Dd April 7, 2004
.Dt MBRLEN 3
.Os
.Sh NAME
.Nm mbrlen
.Nd "get number of bytes in a character (restartable)"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In wchar.h
.Ft size_t
.Fn mbrlen "const char * restrict s" "size_t n" "mbstate_t * restrict ps"
.Sh DESCRIPTION
The
.Fn mbrlen
function inspects at most
.Fa n
bytes pointed to by
.Fa s
to determine the number of bytes needed to complete the next
multibyte character.
.Pp
The
.Vt mbstate_t
argument,
.Fa ps ,
is used to keep track of the shift state.
If it is
.Dv NULL ,
.Fn mbrlen
uses an internal, static
.Vt mbstate_t
object, which is initialized to the initial conversion state
at program startup.
.Pp
It is equivalent to:
.Pp
.Dl "mbrtowc(NULL, s, n, ps);"
.Pp
Except that when
.Fa ps
is a
.Dv NULL
pointer,
.Fn mbrlen
uses its own static, internal
.Vt mbstate_t
object to keep track of the shift state.
.Sh RETURN VALUES
The
.Fn mbrlen
functions returns:
.Bl -tag -width indent
.It 0
The next
.Fa n
or fewer bytes
represent the null wide character
.Pq Li "L'\e0'" .
.It >0
The next
.Fa n
or fewer bytes
represent a valid character,
.Fn mbrlen
returns the number of bytes used to complete the multibyte character.
.It Po Vt size_t Pc Ns \-2
The next
.Fa n
contribute to, but do not complete, a valid multibyte character sequence,
and all
.Fa n
bytes have been processed.
.It Po Vt size_t Pc Ns \-1
An encoding error has occurred.
The next
.Fa n
or fewer bytes do not contribute to a valid multibyte character.
.El
.Sh EXAMPLES
A function that calculates the number of characters in a multibyte
character string:
.Bd -literal -offset indent
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);
}
.Ed
.Sh ERRORS
The
.Fn mbrlen
function will fail if:
.Bl -tag -width Er
.It Bq Er EILSEQ
An invalid multibyte sequence was detected.
.It Bq Er EINVAL
The conversion state is invalid.
.El
.Sh SEE ALSO
.Xr mblen 3 ,
.Xr mbrtowc 3 ,
.Xr multibyte 3
.Sh STANDARDS
The
.Fn mbrlen
function conforms to
.St -isoC-99 .