ncurses/man/curs_getcchar.3x

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.\" $Id: curs_getcchar.3x,v 1.57 2025/02/23 13:48:31 tom Exp $
.TH curs_getcchar 3X 2025-02-23 "ncurses @NCURSES_MAJOR@.@NCURSES_MINOR@" "Library calls"
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.SH NAME
\fB\%getcchar\fP,
\fB\%setcchar\fP \-
convert between a wide-character string and a \fIcurses\fR complex character
.SH SYNOPSIS
.nf
\fB#include <curses.h>
.PP
\fBint getcchar(const cchar_t * \fIwch\fP, wchar_t * \fIwc\fP,
      attr_t * \fIattrs\fP, short * \fIpair\fP, void * \fIopts\fP);
\fBint setcchar(cchar_t * \fIwch\fP, const wchar_t * \fIwc\fP,
      const attr_t \fIattrs\fP, short \fIpair\fP, const void * \fIopts\fP);
.fi
.SH DESCRIPTION
The
.I curses
complex character data type
.I \%cchar_t
is a structure type comprising
a wide-character string,
a set of attributes,
and
a color pair identifier.
The
.I \%cchar_t
structure is opaque;
do not attempt to access its members directly.
The library provides functions to manipulate this type.
.SS getcchar
.B \%getcchar
destructures a
.I \%cchar_t
into its components.
.PP
If
.I wc
is not a null pointer,
.BR \%getcchar :
.bP
stores the wide-character string in the
.I curses
complex character
.I wch
into
.IR wc ;
.bP
stores the attributes in
.IR attrs ;
and
.bP
stores the color pair identifier in
.IR pair .
.PP
If
.I wc
is a null pointer,
.B \%getcchar
counts the
.I \%wchar_t
wide characters in
.IR wch ,
returns that value,
and leaves
.I attrs
and
.I pair
unchanged.
.SS setcchar
.B \%setcchar
constructs a
.I curses
complex character
.I wch
from the components
.IR wc ,
.IR attrs ,
and
.IR pair .
The wide-character string
.I wch
must be terminated with a null wide character
.B L\*'\e0\*'
and must contain at most one spacing character,
which,
if present,
must be the first wide character in the string.
.PP
Up to
.BR \%CCHARW_MAX\  \-\ 1
non-spacing characters may follow
(see \fB\%curs_variables\fP(3X)).
.I \%ncurses
ignores any additional non-spacing characters.
.PP
The string may contain a single control character instead.
In that case,
no non-spacing characters are allowed.
.SH RETURN VALUE
If
.B \%getcchar
is passed a null pointer as its
.I wc
argument,
it returns the number of wide characters for a given
.I wch
that it would store in
.IR wc ","
counting a trailing null wide character.
If
.B \%getcchar
is not passed a null pointer as its
.I wc
argument,
it returns
.B OK
on success and
.B ERR
on failure.
.PP
In
.IR \%ncurses ,
.B \%getcchar
returns
.B ERR
if either
.I attrs
or
.I pair
is a null pointer and
.I wc
is not.
.PP
.B \%setcchar
returns
.B OK
on success and
.B ERR
on failure.
.PP
In
.IR \%ncurses ,
.B \%setcchar
returns
.B ERR
if
.bP
.I wch
is a null pointer,
.bP
.I wc
starts with a (wide) control character
and contains any other wide characters,
or
.bP
.I pair
has a negative value.
.SH NOTES
.I wch
may be a value stored by
.B \%setcchar
or another
.I curses
function with a writable
.I \%cchar_t
argument.
If
.I wch
is constructed by any other means,
the library's behavior is unspecified.
.SH EXTENSIONS
X/Open Curses documents the
.I opts
argument as reserved for future use,
saying that it must be a null pointer.
The
.IR \%ncurses \ 6
ABI uses it with functions that have a color pair parameter
to support extended color pairs.
.bP
In functions that assign colors,
such as
.BR \%setcchar ","
if
.I opts
is not a null pointer,
.I \%ncurses
treats it as a pointer to
.IR int ","
and interprets it instead of the
.I short
.I pair
parameter as a color pair identifier.
.bP
In functions that retrieve colors,
such as
.BR \%getcchar ","
if
.I opts
is not a null pointer,
.I \%ncurses
treats it as a pointer to
.IR int ","
and stores the retrieved color pair identifier there
as well as in the
.I short
.I pair
parameter
(which may therefore undergo a narrowing conversion).
.SH PORTABILITY
Applications employing
.I \%ncurses
extensions should condition their use on the visibility of the
.B \%NCURSES_VERSION
preprocessor macro.
.PP
These functions are described in X/Open Curses Issue\ 4.
It specifies no error conditions for them.
.PP
X/Open Curses does not detail the layout of the
.I \%cchar_t
structure,
describing only its minimal required contents:
.bP
a spacing wide character
.RI \%( wchar_t ),
.bP
at least five non-spacing wide characters
.RI \%( wchar_t ;
see below),
.bP
attributes
(at least 15 bits' worth,
inferred from the count of specified
.I WA_
constants),
.\" See X/Open Curses Issue 7, p. 307.
.bP
a color pair identifier
(at least 16 bits,
inferred from the
.I short
type used to encode it).
.PP
Non-spacing characters are optional,
in the sense that zero or more may be stored in a
.IR \%cchar_t "."
XOpen/Curses specifies a limit:
.RS 4
.PP
Implementations may limit the number of non-spacing characters that can
be associated with a spacing character,
provided any limit is at least 5.
.RE
.PP
Then-contemporary Unix implementations adhered to that limit.
.bP
AIX\ 4 and OSF/1\ 4 used the same declaration with
a single spacing wide character
.I c
and an array of 5 non-spacing wide characters
.IR z "."
.bP
HP-UX\ 10 used an opaque structure of 28 bytes,
large enough for 6
.I \%wchar_t
values.
.bP
Solaris
.I xcurses
uses a single array of 6
.I \%wchar_t
values.
.PP
.I \%ncurses
defined its
.I \%cchar_t
in 1995 using 5 as the
.I total
of spacing and non-spacing characters
.RB \%( CCHARW_MAX ).
That was probably due to a misreading of the AIX\ 4 header files,
because the X/Open Curses document
was not generally available at that time.
Later (in 2002),
this detail was overlooked when work began to implement the functions
using the structure.
.PP
In practice,
a mere four non-spacing characters may seem adequate.
X/Open Curses documents possible applications of non-spacing characters,
including their use as ligatures
(a feature apparently not supported by any
.I curses
implementation).
Unicode does not limit the (analogous) number of combining characters
in a grapheme cluster;
some applications may be affected.
.I \%ncurses
can be compiled with a different
.B CCHARW_MAX
value;
doing so alters the library's ABI.
.SH HISTORY
X/Open Curses Issue\ 4 (1995) initially specified these functions.
.SH SEE ALSO
\fB\%curses\fP(3X),
\fB\%curs_attr\fP(3X),
\fB\%curs_color\fP(3X),
\fB\%wcwidth\fP(3)