.\"	$NetBSD: c32rtomb.3,v 1.11 2024/08/20 20:36:30 riastradh Exp $
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.Dd August 14, 2024
.Dt C32RTOMB 3
.Os
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh NAME
.Nm c32rtomb
.Nd Restartable UTF-32 to multibyte conversion
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh LIBRARY
.Lb libc
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh SYNOPSIS
.
.In uchar.h
.
.Ft size_t
.Fo c32rtomb
.Fa "char * restrict s"
.Fa "char32_t c32"
.Fa "mbstate_t * restrict ps"
.Fc
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh DESCRIPTION
The
.Nm
function converts Unicode scalar values to multibyte characters in the
current locale, keeping state to remember incremental progress if
restarted.
.Pp
Each call to
.Nm
updates the conversion state
.Fa ps
with a UTF-32 code unit
.Fa c32 ,
writes up to
.Dv MB_CUR_MAX
bytes to
.Fa s ,
and returns either the number of bytes written to
.Fa s
or
.Li (size_t)-1
to denote error.
.Pp
The input
.Fa c32
is a UTF-32 code unit, representing a Unicode scalar value, i.e., a
Unicode code point that is not a surrogate code point \(em in other
words,
.Fa c32
is an integer either in [0,0xd7ff] or in [0xe000,0x10ffff].
.Pp
If
.Fa s
is a null pointer,
no output is produced and
.Fa ps
is reset to the initial conversion state, as if the call had been
.Fo c8rtomb
.Va buf ,
.Li 0 ,
.Fa ps
.Fc
for some internal buffer
.Va buf .
.Pp
If
.Fa c32
is zero,
.Nm
outputs a (possibly empty) shift sequence to restore the initial state
followed by a NUL byte and resets
.Fa ps
to the initial conversion state.
.Pp
If
.Fa ps
is a null pointer,
.Nm
uses an internal
.Vt mbstate_t
object with static storage duration, distinct from all other
.Vt mbstate_t
objects
.Po
including those used by other functions such as
.Xr mbrtoc32 3
.Pc ,
which is initialized at program startup to the initial conversion
state.
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.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 sequence of Unicode scalar values to a multibyte sequence,
NUL-terminate it (with any shift sequence needed to restore the initial
state), and print it:
.Bd -literal -offset indent
char32_t c32[] = { 0x1f4a9, 0x20ac, 0x21 };
char buf[(__arraycount(c32) + 1)*MB_LEN_MAX], *s = buf;
size_t i;
mbstate_t mbs = {0};    /* initial conversion state */

for (i = 0; i < __arraycount(c32); i++) {
        size_t len;

        len = c32rtomb(s, c32[i], &mbs);
        if (len == (size_t)-1)
                err(1, "c32rtomb");
        assert(len < sizeof(buf) - (s - buf));
        s += len;
}
len = c32rtomb(s, 0, &mbs);             /* NUL-terminate */
if (len == (size_t)-1)
        err(1, "c32rtomb");
assert(len <= sizeof(buf) - (s - buf));
printf("%s\en", buf);
.Ed
.Pp
To avoid a variable-length array, this code uses
.Dv MB_LEN_MAX ,
which is a constant upper bound on the locale-dependent
.Dv MB_CUR_MAX .
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh ERRORS
.Bl -tag -width Bq
.It Bq Er EILSEQ
.Fa c32
is not a Unicode scalar value, i.e., it is a surrogate code point in
the interval [0xd800,0xdfff] or it lies outside the Unicode codespace
[0,0x10ffff] altogether.
.It Bq Er EILSEQ
The input cannot be encoded as a multibyte sequence in the current
locale.
.It Bq Er EIO
An error occurred in loading the locale's character conversions.
.El
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh SEE ALSO
.Xr c16rtomb 3 ,
.Xr c8rtomb 3 ,
.Xr mbrtoc16 3 ,
.Xr mbrtoc32 3 ,
.Xr mbrtoc8 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
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh STANDARDS
The
.Nm
function conforms to
.St -isoC-2011 .
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh HISTORY
The
.Nm
function first appeared in
.Nx 11.0 .