.\" $NetBSD: mblen.3,v 1.2 2002/03/18 07:56:28 wiz Exp $
.\"
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.Dd February 3, 2002
.Dt MBLEN 3
.Os
.\" ----------------------------------------------------------------------
.Sh NAME
.Nm mblen
.Nd get number of bytes consisting a multibyte character
.\" ----------------------------------------------------------------------
.Sh LIBRARY
.Lb libc
.\" ----------------------------------------------------------------------
.Sh SYNOPSIS
.Fd #include \*[Lt]stdlib.h\*[Gt]
.Ft int
.Fn mblen "const char *s" "size_t n"
.\" ----------------------------------------------------------------------
.Sh DESCRIPTION
The
.Fn mblen
function usually determines the number of bytes consisting in
a multibyte character pointed by
.Fa s
and return it.
This function shall only examine max n bytes of the array beginning from
.Fa s .
.Pp
In state-dependent encodings,
.Fa s
may point the special sequence bytes to change the shift-state.
Although such sequence bytes corresponds to no individual
wide-character code,
the
.Fn mblen
changes the own state by them and treats them
as if they are a part of the subsequence multibyte character.
.Pp
Unlike
.Xr mbrlen 3 ,
the first
.Fa n
bytes pointed by
.Fa s
need to form an entire multibyte character.
Otherwise, this function causes an error.
.Pp
.Fn mblen
is equivalent to the following call, except the internal state of the
.Xr mbtowc 3
function is not affected:
.Pp
.Bd -literal
mbtowc(NULL, s, n);
.Ed
.Pp
Calling any other functions in the
.Lb libc
never change the internal
state of the
.Fn mblen ,
except for calling
.Xr setlocale 3
with changing LC_CTYPE category of the current locale.
Such
.Xr setlocale 3
call causes the internal state of this function to be indeterminate.
.Pp
The behaviour of the
.Fn mblen
is affected by LC_CTYPE category of the current locale.
.Pp
There are special cases:
.Bl -tag -width 0123456789
.It "s == NULL"
The
.Fn 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.
.It "n == 0"
In this case,
the first
.Fa n
bytes of the array pointed by
.Fa s
never form a complete character.  Thus, the
.Fn mblen
always fails.
.El
.\" ----------------------------------------------------------------------
.Sh RETURN VALUES
In the usual cases, the
.Fn mblen
returns:
.Bl -tag -width 0123456789
.It "0"
.Fa s
points a null byte (\'\\0\').
.It "positive"
The value returned is
a number of bytes for the valid multibyte character pointed by
.Fa s .
There is no cases that this value is greater than
.Fa n
or the value of MB_CUR_MAX macro.
.It "-1"
.Fa s
points an invalid or incomplete multibyte character.
The
.Fn mblen
also sets errno to indicate the error.
.El
.Pp
In the case that
.Fa s
is equal to NULL, the
.Fn mblen
returns:
.Bl -tag -width 0123456789
.It "0"
The current encoding is state-independent.
.It "non-zero"
The current encoding is state-dependent.
.El
.\" ----------------------------------------------------------------------
.Sh ERRORS
The
.Fn mblen
may causes an error in the following case:
.Bl -tag -width Er
.It Bq Er EILSEQ
.Fa s
points an invalid or incomplete multibyte character.
.El
.\" ----------------------------------------------------------------------
.Sh SEE ALSO
.Xr mbrlen 3 ,
.Xr mbtowc 3 ,
.Xr setlocale 3
.\" ----------------------------------------------------------------------
.Sh STANDARDS
The
.Fn mblen
function conforms to
.St -ansiC .