.Dd 10 March 2024
.Dt RTOU8 3
.Os
.Sh NAME
.Nm rtou8
.Nd encode a rune to UTF-8
.Sh LIBRARY
.Lb mlib
.Sh SYNOPSIS
.In mbstring.h
.Ft int
.Fn rtou8 "char8_t *s" "size_t n" "rune ch"
.Sh DESCRIPTION
The
.Fn rtou8
function writes the rune
.Fa ch
to the UTF-8 encoded buffer
.Fa s
of length
.Fa n ,
returning the number of bytes required to UTF-8 encode
.Fa ch .
If
.Fa s
is too small,
no data is written to it but the number of bytes required to UTF-8 encode
.Fa ch
is still returned.
.Pp
An invalid rune is treated as if it were
.Dv RUNE_ERROR .
.Sh RETURN VALUES
The
.Fn rtou8
function returns the number of bytes required to write
.Fa ch
to the buffer
.Fa s .
.Sh EXAMPLES
The following call to
.Fn rtou8
is used to print a rune to the standard output.
.Bd -literal -offset indent
#include <rune.h> /* For PRIXRUNE; see rune(3) */

rune ch = U\(aqĦ\(aq;
char buf[U8_LEN_MAX];
int w = rtou8(buf, sizeof(buf), ch);

/* U+0126: ‘Ħ’ */
printf(\(dqU+%04\(dq PRIXRUNE \(dq: ‘%.*s’\en\(dq, ch, w, buf);
.Ed
.Sh SEE ALSO
.Xr rune 3 ,
.Xr u8tor 3 ,
.Xr RUNE_ERROR 3const ,
.Xr unicode 7 ,
.Xr utf\-8 7
.Sh STANDARDS
.Rs
.%A F. Yergeau
.%D November 2003
.%R RFC 3629
.%T UTF-8, a transformation format of ISO 10646
.Re
.Sh AUTHORS
.An Thomas Voss Aq Mt mail@thomasvoss.com