.\" $NetBSD: mblen.3,v 1.7 2024/02/03 10:55:38 rillig Exp $
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.Dd February 3, 2024
.Dt MBLEN 3
.Os
.\" ----------------------------------------------------------------------
.Sh NAME
.Nm mblen
.Nd get number of bytes in a multibyte character
.\" ----------------------------------------------------------------------
.Sh LIBRARY
.Lb libc
.\" ----------------------------------------------------------------------
.Sh SYNOPSIS
.In stdlib.h
.Ft int
.Fn mblen "const char *s" "size_t n"
.\" ----------------------------------------------------------------------
.Sh DESCRIPTION
The
.Fn mblen
function usually determines the number of bytes in
a multibyte character pointed to by
.Fa s
and returns it.
This function examines at most
.Fa n
bytes of the array beginning from
.Fa s .
.Pp
In state-dependent encodings,
.Fa s
may point to the special sequence bytes to change the shift-state.
Although such sequence bytes corresponds to no individual
wide-character code,
the
.Fn mblen
function changes its own state by them and treats them
as if they were part of the subsequent multibyte character.
.Pp
Unlike
.Xr mbrlen 3 ,
the first
.Fa n
bytes pointed to 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:
.Bd -literal -offset indent
mbtowc(NULL, s, n);
.Ed
.Pp
Calling any other functions in
.Lb libc
never changes the internal
state of
.Fn mblen ,
except for calling
.Xr setlocale 3
with the
.Dv LC_CTYPE
category changed to that of the current locale.
Such
.Xr setlocale 3
calls cause the internal state of this function to be indeterminate.
.Pp
The behaviour of
.Fn mblen
is affected by the
.Dv LC_CTYPE
category of the current locale.
.Pp
These are the special cases:
.Bl -tag -width 0123456789
.It "s == NULL"
.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"
The first
.Fa n
bytes of the array pointed to by
.Fa s
never form a complete character.
Thus,
.Fn mblen
always fails.
.El
.\" ----------------------------------------------------------------------
.Sh RETURN VALUES
Normally,
.Fn mblen
returns:
.Bl -tag -width 0123456789
.It "0"
.Fa s
points to a nul byte
.Pq Sq \e0 .
.It "positive"
The value returned is
the number of bytes for the valid multibyte character pointed to by
.Fa s .
The value returned is at most
.Fa n ,
and at most the value of the
.Dv MB_CUR_MAX
macro.
.It "-1"
.Fa s
points to an invalid or incomplete multibyte character.
The
.Fn mblen
function also sets
.Va errno
to indicate the error.
.El
.Pp
When
.Fa s
is equal to
.Dv NULL ,
the
.Fn mblen
function 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
.Fn mblen
may cause an error in the following case:
.Bl -tag -width Er
.It Bq Er EILSEQ
.Fa s
points to 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 .