.\" Copyright (c) 2002 Tim J. Robbins
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.Dd November 11, 2002
.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 determines the number of bytes constituting the
multibyte character sequence pointed to by
.Fa s ,
examining at most
.Fa n
bytes.
.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.
.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 first
.Fa n
or fewer bytes of
.Fa s
represent the null wide character
.Pq Li "L'\e0'" .
.It >0
The first
.Fa n
or fewer bytes of
.Fa s
represent a valid character,
.Fn mbrtowc
returns the length (in bytes) of the multibyte sequence.
.It Po Vt size_t Pc Ns \-2
The first
.Fa n
bytes of
.Fa s
are an incomplete multibyte sequence.
.It Po Vt size_t Pc Ns \-1
The byte sequence pointed to by
.Fa s
is an invalid multibyte sequence.
.El
.Sh EXAMPLES
A function which 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 EINVAL
.\"Invalid argument.
.It Bq Er EILSEQ
An invalid multibyte sequence was detected.
.El
.Sh SEE ALSO
.Xr mblen 3 ,
.Xr mbrtowc 3
.Sh STANDARDS
The
.Fn mbrlen
function conforms to
.St -isoC-99 .
.Sh BUGS
The current implementation does not support shift states.