man3/mbtowc.3

.\" Copyright (c) Bruno Haible <haible@clisp.cons.org>
.\"
.\" %%%LICENSE_START(GPLv2+_DOC_ONEPARA)
.\" This is free documentation; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License as
.\" published by the Free Software Foundation; either version 2 of
.\" the License, or (at your option) any later version.
.\" %%%LICENSE_END
.\"
.\" 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 MBTOWC 3  2021-03-22 "GNU" "Linux Programmer's Manual"
.SH NAME
mbtowc \- convert a multibyte sequence to a wide character
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.PP
.BI "int mbtowc(wchar_t *restrict " pwc ", const char *restrict " s \
", size_t " n );
.fi
.SH DESCRIPTION
The main case for this function is when
.IR s
is not NULL and
.I pwc
is
not NULL.
In this case, the
.BR mbtowc ()
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 an internal shift state known only to the
.BR mbtowc ()
function.
If
.I s
does not point to a null byte (\(aq\e0\(aq), it returns the number
of bytes that were consumed from
.IR s ,
otherwise it returns 0.
.PP
If the
.IR n
bytes starting at
.I s
do not contain a complete multibyte
character, or if they contain an invalid multibyte sequence,
.BR mbtowc ()
returns \-1.
This can happen even if
.I n
>=
.IR MB_CUR_MAX ,
if the multibyte string contains redundant shift sequences.
.PP
A different case is when
.IR s
is not NULL but
.I pwc
is NULL.
In this case, the
.BR mbtowc ()
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,
.IR pwc
and
.I n
are
ignored.
The
.BR mbtowc ()
function
.\" The Dinkumware doc and the Single UNIX specification say this, but
.\" glibc doesn't implement this.
resets the shift state, only known to this function,
to the initial state, and
returns nonzero if the encoding has nontrivial shift state, or zero if the
encoding is stateless.
.SH RETURN VALUE
If
.I s
is not NULL, the
.BR mbtowc ()
function returns the number of
consumed bytes starting at
.IR s ,
or 0 if
.I s
points to a null byte,
or \-1 upon failure.
.PP
If
.I s
is NULL, the
.BR mbtowc ()
function
returns nonzero if the encoding
has nontrivial shift state, or zero if the encoding is stateless.
.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 mbtowc ()
T}	Thread safety	MT-Unsafe race
.TE
.hy
.ad
.sp 1
.SH CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C99.
.SH NOTES
The behavior of
.BR mbtowc ()
depends on the
.B LC_CTYPE
category of the
current locale.
.PP
This function is not multithread safe.
The function
.BR mbrtowc (3)
provides
a better interface to the same functionality.
.SH SEE ALSO
.BR MB_CUR_MAX (3),
.BR mblen (3),
.BR mbrtowc (3),
.BR mbstowcs (3),
.BR wcstombs (3),
.BR wctomb (3)