libc/locale/mbrlen.3

.\" $OpenBSD: mbrlen.3,v 1.4 2013/06/05 03:39:22 tedu Exp $
.\" $NetBSD: mbrlen.3,v 1.5 2003/09/08 17:54:31 wiz Exp $
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.Dd $Mdocdate: June 5 2013 $
.Dt MBRLEN 3
.Os
.\" ----------------------------------------------------------------------
.Sh NAME
.Nm mbrlen
.Nd get number of bytes in a multibyte character (restartable)
.\" ----------------------------------------------------------------------
.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 usually determines the number of bytes in
a multibyte character pointed to by
.Fa s
and returns it.
This function shall only examine max n bytes of the array beginning from
.Fa s .
.Pp
.Fn mbrlen
is equivalent to the following call (except
.Fa ps
is evaluated only once):
.Bd -literal -offset indent
mbrtowc(NULL, s, n, (ps != NULL) ? ps : &internal);
.Ed
.Pp
Here,
.Fa internal
is an internal state object.
.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, these affect the conversion state object pointed to by
.Fa ps ,
and the
.Fn mbrlen
treats the special sequence bytes
as if these are a part of the subsequent multibyte character.
.Pp
Unlike
.Xr mblen 3 ,
.Fn mbrlen
may accept the byte sequence when it is not a complete character
but possibly contains part of a valid character.
In this case, this function will accept all such bytes
and save them into the conversion state object pointed to by
.Fa ps .
They will be used on subsequent calls of this function to restart
the conversion suspended.
.Pp
The behaviour of the
.Fn mbrlen
is affected by
.Dv LC_CTYPE
category of the current locale.
.Pp
There are the special cases:
.Bl -tag -width 0123456789
.It "s == NULL"
.Fn mbrlen
sets the conversion state object pointed to by
.Fa ps
to an initial state and always returns 0.
Unlike
.Xr mblen 3 ,
the value returned does not indicate whether the current encoding of
the locale is state-dependent.
.Pp
In this case,
.Fn mbrlen
ignores
.Fa n .
.It "n == 0"
In this case,
the first
.Fa n
bytes of the array pointed to by
.Fa s
never form a complete character.
Thus,
.Fn mbrlen
always returns (size_t)-2.
.It "ps == NULL"
.Fn mbrlen
uses its own internal state object to keep the conversion state,
instead of
.Fa ps
mentioned in this manual page.
.Pp
Calling any other functions in
.Em libc
never change the internal
state of
.Fn mbrlen ,
except for calling
.Xr setlocale 3
with a changing
.Dv LC_CTYPE
category of the current locale.
Such
.Xr setlocale 3
calls cause the internal state of this function to be indeterminate.
This internal state is initialized at startup time of the program.
.El
.\" ----------------------------------------------------------------------
.Sh RETURN VALUES
The
.Fn mbrlen
returns:
.Bl -tag -width 0123456789
.It "0"
.Fa s
points to a null byte
.Pq Sq \e0 .
.It "positive"
The value returned is
a number of bytes for the valid multibyte character pointed to by
.Fa s .
There are no cases where this value is greater than
.Fa n
or the value of the
.Dv MB_CUR_MAX
macro.
.It "(size_t)-2"
.Fa s
points to the byte sequence which possibly contains part of a valid
multibyte character, but which is incomplete.
When
.Fa n
is at least
.Dv MB_CUR_MAX
can only occur if the array pointed to by
.Fa s
contains a redundant shift sequence.
.It "(size_t)-1"
.Fa s
points to an illegal byte sequence which does not form a valid multibyte
character.
In this case,
.Fn mbrtowc
sets
.Va errno
to indicate the error.
.El
.\" ----------------------------------------------------------------------
.Sh ERRORS
.Fn mbrlen
may cause an error in the following cases:
.Bl -tag -width Er
.It Bq Er EILSEQ
.Fa s
points to an invalid multibyte character.
.It Bq Er EINVAL
.Fa ps
points to an invalid or uninitialized mbstate_t object.
.El
.\" ----------------------------------------------------------------------
.Sh SEE ALSO
.Xr mblen 3 ,
.Xr mbrtowc 3 ,
.Xr setlocale 3
.\" ----------------------------------------------------------------------
.Sh STANDARDS
The
.Fn mbrlen
function conforms to
.\" .St -isoC-amd1 .
ISO/IEC 9899/AMD1:1995
.Pq Dq ISO C90, Amendment 1 .
The restrict qualifier is added at
.\" .St -isoC99 .
ISO/IEC 9899/1999
.Pq Dq ISO C99 .