.\"	$NetBSD: mbrtoc32.3,v 1.9 2024/08/23 12:59:49 riastradh Exp $
.\"
.\" 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 MBRTOC32 3
.Os
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh NAME
.Nm mbrtoc32
.Nd Restartable multibyte to UTF-32 conversion
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh LIBRARY
.Lb libc
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh SYNOPSIS
.
.In uchar.h
.
.Ft size_t
.Fo mbrtoc32
.Fa "char32_t * restrict pc32"
.Fa "const char * restrict s"
.Fa "size_t n"
.Fa "mbstate_t * restrict ps"
.Fc
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh DESCRIPTION
The
.Nm
function decodes multibyte characters in the current locale and
converts them to Unicode scalar values (i.e., to UTF-32), keeping state
so it can restart after incremental progress.
.Pp
Each call to
.Nm :
.Bl -enum -compact
.It
examines up to
.Fa n
bytes starting at
.Fa s ,
.It
yields a Unicode scalar value (i.e., a UTF-32 code unit) if available
by storing it at
.Li * Ns Fa pc32 ,
.It
saves state at
.Fa ps ,
and
.It
returns either the number of bytes consumed if any or a special return
value.
.El
.Pp
Specifically:
.Bl -bullet
.It
If the multibyte sequence at
.Fa s
is invalid after any previous input saved at
.Fa ps ,
or if an error occurs in decoding,
.Nm
returns
.Li (size_t)-1
and sets
.Xr errno 2
to indicate the error.
.It
If the multibyte sequence at
.Fa s
is still incomplete after
.Fa n
bytes, including any previous input saved in
.Fa ps ,
.Nm
saves its state in
.Fa ps
after all the input so far and returns
.Li "(size_t)-2".
.It
If
.Nm
decodes the null multibyte character, then it stores zero at
.Li * Ns Fa pc32
and returns zero.
.It
Otherwise,
.Nm
decodes a single multibyte character, stores its Unicode scalar value
at
.Li * Ns Fa pc32 ,
and returns the number of bytes consumed to decode the first multibyte
character.
.El
.Pp
If
.Fa pc32
is a null pointer, nothing is stored, but the effects on
.Fa ps
and the return value are unchanged.
.Pp
If
.Fa s
is a null pointer, the
.Nm
call is equivalent to:
.Bd -ragged -offset indent
.Fo mbrtoc32
.Li NULL ,
.Li \*q\*q ,
.Li 1 ,
.Fa ps
.Fc
.Ed
.Pp
This always returns zero, and has the effect of resetting
.Fa ps
to the initial conversion state, without writing to
.Fa pc32 ,
even if it is nonnull.
.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
.Xr mbrtoc8 3 ,
.Xr mbrtoc16 3 ,
.Xr c8rtomb 3 ,
.Xr c16rtomb 3 ,
and
.Xr c32rtomb 3
.Pc ,
which is initialized at program startup to the initial conversion
state.
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh RETURN VALUES
The
.Nm
function returns:
.Bl -tag -width Li
.It Li 0
.Bq null
if
.Nm
decoded a null multibyte character.
.It Ar i
.Bq scalar value
where
.Li 0
\*(Le
.Ar i
\*(Le
.Fa n ,
if
.Nm
consumed
.Ar i
bytes of input to decode the next multibyte character, yielding a
Unicode scalar value.
.It Li (size_t)-2
.Bq incomplete
if
.Nm
found only an incomplete multibyte sequence after all
.Fa n
bytes of input and any previous input, and saved its state to restart
in the next call with
.Fa ps .
.It Li (size_t)-1
.Bq error
if any encoding error was detected;
.Xr errno 2
is set to reflect the error.
.El
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh EXAMPLES
.Bd -literal -offset indent
char *s = ...;
size_t n = ...;
mbstate_t mbs = {0};    /* initial conversion state */

while (n) {
        char32_t c32;
        size_t len;

        len = mbrtoc32(&c32, s, n, &mbs);
        switch (len) {
        case 0:                 /* NUL terminator */
                assert(c32 == 0);
                goto out;
        default:                /* scalar value */
                printf("U+%04"PRIx32"\en", (uint32_t)c32);
                break;
        case (size_t)-2:        /* incomplete */
                printf("incomplete\en");
                goto readmore;
        case (size_t)-1:        /* error */
                printf("error: %d\en", errno);
                goto out;
        }
        s += len;
        n -= len;
}
.Ed
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh ERRORS
.Bl -tag -width Bq
.It Bq Er EILSEQ
The multibyte sequence cannot be decoded in the current locale as a
Unicode scalar value.
.It Bq Er EIO
An error occurred in loading the locale's character conversions.
.El
.\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.Sh SEE ALSO
.Xr c16rtomb 3 ,
.Xr c32rtomb 3 ,
.Xr c8rtomb 3 ,
.Xr mbrtoc16 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 .