Copyright (c) 2024 The NetBSD Foundation, Inc.
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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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 August 14, 2024 .Dt C16RTOMB 3 .Os """"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh NAME .Nm c16rtomb .Nd Restartable UTF-16 code unit to multibyte conversion """"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh LIBRARY .Lb libc """"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh SYNOPSIS . n uchar.h . .Ft size_t .Fo c16rtomb .Fa "char * restrict s" .Fa "char16_t c16" .Fa "mbstate_t * restrict ps" .Fc """"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh DESCRIPTION The .Nm function attempts to encode Unicode input as a multibyte character sequence output at .Fa s in the current locale, writing anywhere between zero and .Dv MB_CUR_MAX bytes, inclusive, to .Fa s , depending on the inputs and conversion state .Fa ps .
p The input .Fa c16 is a UTF-16 code unit, which can be either: l -bullet t a Unicode scalar value in the Basic Multilingual Plane (BMP), that is, a 16-bit code unit outside the interval [0xd800,0xdfff]; or, t over the course of two consecutive calls to .Nm , the high and low surrogate code points of a Unicode scalar value outside the BMP. .El
p
If a low surrogate code point, that is, a value of
.Fa c16
in [0xdc00,0xdfff], is passed to
.Nm
without the preceding call to it with the same
.Fa ps
having been passed a high surrogate code point, that is, a value of
.Fa c16
in [0xd800,0xdbff], or if a high surrogate was passed in the previous
call and anything other than a low surrogate is passed, then
.Nm
will return
.Li (size_t)-1
to denote failure with
.Xr errno 2
set to
.Er EILSEQ .
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh RETURN VALUES
The
.Nm
function returns the number of bytes written to
.Fa s
on success, or sets
.Xr errno 2
and returns
.Li "(size_t)-1"
on failure.
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh EXAMPLES
Convert a UTF-16 code unit sequence to a multibyte string,
NUL-terminate it, and print it:
d -literal -offset indent char16_t c16[] = { 0xd83d, 0xdca9 };
char buf[__arraycount(c16)*MB_CUR_MAX + 1], *s = buf;
size_t i;
mbstate_t mbs = {0}; /* initial conversion state */
for (i = 0; i < __arraycount(c16); i++) {
size_t len;
len = c16rtomb(s, c16[i], &mbs);
if (len == (size_t)-1)
err(1, "c16rtomb");
assert(len < sizeof(buf) - (s - buf));
s += len;
}
*s = '\e0'; /* NUL-terminate */
printf("%s\en", buf);
.Ed
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh ERRORS
l -tag -width Bq t Bq Er EILSEQ A surrogate code point was passed as
.Fa c16
when it is inappropriate.
t Bq Er EILSEQ The Unicode scalar value requested cannot be encoded as a multibyte
sequence in the current locale.
t Bq Er EIO An error occurred in loading the locale's character conversions.
.El
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh SEE ALSO
.Xr c32rtomb 3 ,
.Xr mbrtoc16 3 ,
.Xr mbrtoc32 3 ,
.Xr uchar 3
.Rs
.%B The Unicode Standard
.%O Version 15.0 \(em Core Specification
.%Q The Unicode Consortium
.%D September 2022
.%U https://www.unicode.org/versions/Unicode15.0.0/UnicodeStandard-15.0.pdf
.Re
.Rs
.%A P. Hoffman
.%A F. Yergeau
.%T UTF-16, an encoding of ISO 10646
.%R RFC 2781
.%D February 2000
.%I Internet Engineering Task Force
.%U https://datatracker.ietf.org/doc/html/rfc2781
.Re
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh STANDARDS
The
.Nm
function conforms to
.St -isoC-2011 .
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh HISTORY
The
.Nm
function first appeared in
.Nx 11.0 .
""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh BUGS
It is not clear from the standard how
.Nm
is supposed to behave when given a high surrogate code point followed
by a NUL:
d -literal -offset indent c16rtomb(s, 0xd800, ps);
c16rtomb(s, L'\e0', ps);
.Ed
p Currently this fails with .Er EILSEQ which matches other implementations, but this is at odds with language in the standard which suggests that passing .Li L'\e0' should unconditionally store a null byte and reset .Fa ps to the initial conversion state: d -filled -offset indent If .Fa c16 is a null wide character, a null byte is stored, preceded by any shift sequence needed to restore the initial shift state; the resulting state described is the initial conversion state. .Ed
p However, it is unclear what else this should store besides a null byte. Should it discard the pending high surrogate, or convert it to something else and store that?
Indexes created Sun Oct 12 05:10:08 GMT 2025