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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 . n 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.
p 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.
p 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].
p 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 .
p 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.
p 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
o including those used by other functions such as .Xr mbrtoc32 3
c ,
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:
d -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
p
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
l -tag -width Bq t 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.
t Bq Er EILSEQ The input 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 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 .
Indexes created Sat Oct 11 14:09:46 GMT 2025