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.\" $OpenBSD: mbtowc.3,v 1.3 2010/11/20 18:23:19 stsp Exp $
.\" $NetBSD: mbtowc.3,v 1.5 2003/09/08 17:54:31 wiz Exp $
.\"
.\" Copyright (c)2002 Citrus Project,
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd $Mdocdate: November 20 2010 $
.Dt MBTOWC 3
.Os
.\" ----------------------------------------------------------------------
.Sh NAME
.Nm mbtowc
.Nd converts a multibyte character to a wide character
.\" ----------------------------------------------------------------------
.Sh SYNOPSIS
.Fd #include <stdlib.h>
.Ft int
.Fn mbtowc "wchar_t * restrict pwc" "const char * restrict s" "size_t n"
.Sh DESCRIPTION
The
.Fn mbtowc
usually converts the multibyte character pointed to by
.Fa s
to a wide character, and stores it in the wchar_t object pointed to by
.Fa pwc
if
.Fa pwc
is non-null and
.Fa s
points to a valid character.
This function may inspect at most 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 correspond to no individual
wide-character code,
.Fn mbtowc
changes its own state by the sequence bytes and treats them
as if they are a part of the subsequence multibyte character.
.Pp
Unlike
.Xr mbrtowc 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
Calling any other functions in
.Em libc
never change the internal
state of the
.Fn mbtowc ,
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 mbtowc
is affected by the
.Dv LC_CTYPE
category of the current locale.
.Pp
These are the special cases:
.Bl -tag -width 012345678901
.It s == NULL
.Fn mbtowc
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.
In this case,
.Fa pwc
is completely ignored.
.It pwc == NULL
.Fn mbtowc
executes the conversion as if
.Fa pwc
is non-null, but a result of the conversion is discarded.
.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, the
.Fn mbtowc
always fails.
.El
.\" ----------------------------------------------------------------------
.Sh RETURN VALUES
Normally,
.Fn mbtowc
returns:
.Bl -tag -width 012345678901
.It 0
.Fa s
points to a null byte
.Pq Sq \e0 .
.It positive
Number of bytes for the valid multibyte character pointed to by
.Fa s .
There are no cases where the value returned is greater than
the value of the
.Dv MB_CUR_MAX
macro.
.It -1
.Fa s
points to an invalid or an incomplete multibyte character.
The
.Fn mbtowc
also sets errno to indicate the error.
.El
.Pp
When
.Fa s
is equal to NULL,
.Fn mbtowc
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 mbtowc
may cause an error in the following cases:
.Bl -tag -width Er
.It Bq Er EILSEQ
.Fa s
points to an invalid or incomplete multibyte character.
.El
.\" ----------------------------------------------------------------------
.Sh SEE ALSO
.Xr mblen 3 ,
.Xr mbrtowc 3 ,
.Xr setlocale 3
.\" ----------------------------------------------------------------------
.Sh STANDARDS
The
.Fn mbtowc
function conforms to
.St -ansiC .
The restrict qualifier is added at
.\" .St -isoC99 .
ISO/IEC 9899/1999
.Pq Dq ISO C99 .
.Sh CAVEATS
On error, callers of
.Fn mbtowc
cannot tell whether the multibyte character was invalid or incomplete.
To treat incomplete data differently from invalid data the
.Xr mbrtowc 3
function can be used instead.
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