'\" t
.\" Copyright (c) Bruno Haible <haible@clisp.cons.org>
.\"
.\" SPDX-License-Identifier: GPL-2.0-or-later
.\"
.\" References consulted:
.\"   GNU glibc-2 source code and manual
.\"   Dinkumware C library reference http://www.dinkumware.com/
.\"   OpenGroup's Single UNIX specification
.\"      http://www.UNIX-systems.org/online.html
.\"   ISO/IEC 9899:1999
.\"
.TH mbrtowc 3 2023-03-30 "Linux man-pages 6.04"
.SH NAME
mbrtowc \- convert a multibyte sequence to a wide character
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <wchar.h>
.PP
.BI "size_t mbrtowc(wchar_t *restrict " pwc ", const char " s "[restrict ." n ],
.BI "               size_t " n ", mbstate_t *restrict " ps );
.fi
.SH DESCRIPTION
The main case for this function is when
.I s
is not NULL and
.I pwc
is
not NULL.
In this case, the
.BR mbrtowc ()
function inspects at most
.I n
bytes of the multibyte string starting at
.IR s ,
extracts the next complete
multibyte character, converts it to a wide character and stores it at
.IR *pwc .
It updates the shift state
.IR *ps .
If the converted wide
character is not L\[aq]\e0\[aq] (the null wide character),
it returns the number of bytes that were consumed
from
.IR s .
If the converted wide character is L\[aq]\e0\[aq], it resets the shift
state
.I *ps
to the initial state and returns 0.
.PP
If the
.I n
bytes starting at
.I s
do not contain a complete multibyte
character,
.BR mbrtowc ()
returns
.IR "(size_t)\ \-2" .
This can happen even if
.I n
>=
.IR MB_CUR_MAX ,
if the multibyte string contains redundant shift
sequences.
.PP
If the multibyte string starting at
.I s
contains an invalid multibyte
sequence before the next complete character,
.BR mbrtowc ()
returns
.I (size_t)\ \-1
and sets
.I errno
to
.BR EILSEQ .
In this case,
the effects on
.I *ps
are undefined.
.PP
A different case is when
.I s
is not NULL but
.I pwc
is NULL.
In this case, the
.BR mbrtowc ()
function behaves as above, except that it does not
store the converted wide character in memory.
.PP
A third case is when
.I s
is NULL.
In this case,
.I pwc
and
.I n
are
ignored.
If the conversion state represented by
.I *ps
denotes an
incomplete multibyte character conversion, the
.BR mbrtowc ()
function
returns
.IR "(size_t)\ \-1" ,
sets
.I errno
to
.BR EILSEQ ,
and
leaves
.I *ps
in an undefined state.
Otherwise, the
.BR mbrtowc ()
function
puts
.I *ps
in the initial state and returns 0.
.PP
In all of the above cases, if
.I ps
is NULL, a static anonymous
state known only to the
.BR mbrtowc ()
function is used instead.
Otherwise,
.I *ps
must be a valid
.I mbstate_t
object.
An
.I mbstate_t
object
.I a
can be initialized to the initial state
by zeroing it, for example using
.PP
.in +4n
.EX
memset(&a, 0, sizeof(a));
.EE
.in
.SH RETURN VALUE
The
.BR mbrtowc ()
function returns the number of bytes parsed from the
multibyte sequence starting at
.IR s ,
if a non-L\[aq]\e0\[aq] wide character
was recognized.
It returns 0, if a L\[aq]\e0\[aq] wide character was recognized.
It returns
.I (size_t)\ \-1
and sets
.I errno
to
.BR EILSEQ ,
if an invalid multibyte sequence was
encountered.
It returns
.I "(size_t)\ \-2"
if it couldn't parse a complete multibyte
character, meaning that
.I n
should be increased.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR mbrtowc ()
T}	Thread safety	MT-Unsafe race:mbrtowc/!ps
.TE
.hy
.ad
.sp 1
.SH STANDARDS
C11, POSIX.1-2008.
.SH HISTORY
POSIX.1-2001, C99.
.SH NOTES
The behavior of
.BR mbrtowc ()
depends on the
.B LC_CTYPE
category of the
current locale.
.SH SEE ALSO
.BR mbsinit (3),
.BR mbsrtowcs (3)