getcchar(3NCURSES) Library calls getcchar(3NCURSES)
NAME
getcchar, setcchar - convert between a wide-character string and a
curses complex character
SYNOPSIS
#include <curses.h>
int gettchar(const cchar_t * wch, wchar_t * wc,
attr_t * attrs, short * pair, void * opts);
int settchar(cchar_t * wch, const wchar_t * wc,
const attr_t attrs, short pair, const void * opts);
DESCRIPTION
The curses complex character data type cchar_t is a structure type com-
prising a wide-character string, a set of attributes, and a color pair
identifier. The cchar_t structure is opaque; do not attempt to access
its members directly. The library provides functions to manipulate this
type.
getcchar
getcchar destructures a cchar_t into its components.
If wc is not a null pointer, getcchar:
• stores the wide-character string in the curses complex character wch
into wc;
• stores the attributes in attrs; and
• stores the color pair identifier in pair.
If wc is a null pointer, getcchar counts the wchar_t wide characters in
wch, returns that value, and leaves attrs and pair unchanged.
setcchar
setcchar constructs a curses complex character wch from the components
wc, attrs, and pair. The wide-character string wch must be terminated
with a null wide character L'\0' and must contain at most one spacing
character, which, if present, must be the first wide character in the
string.
Up to CCHARW_MAX - 1 non-spacing characters may follow (see
curses_variables(3NCURSES)). ncurses ignores any additional non-spacing
characters.
The string may contain a single control character instead. In that
case, no non-spacing characters are allowed.
RETURN VALUE
If getcchar is passed a null pointer as its wc argument, it returns the
number of wide characters for a given wch that it would store in wc,
counting a trailing null wide character. If getcchar is not passed a
null pointer as its wc argument, it returns OK on success and ERR on
failure.
In ncurses, getcchar returns ERR if either attrs or pair is a null
pointer and wc is not.
setcchar returns OK on success and ERR on failure.
In ncurses, setcchar returns ERR if
• wch is a null pointer,
• wc starts with a (wide) control character and contains any other
wide characters, or
• pair has a negative value.
NOTES
wch may be a value stored by setcchar or another curses function with a
writable cchar_t argument. If wch is constructed by any other means,
the library's behavior is unspecified.
EXTENSIONS
X/Open Curses documents the opts argument as reserved for future use,
saying that it must be a null pointer. The ncurses 6 ABI uses it with
functions that have a color pair parameter to support extended color
pairs.
• In functions that assign colors, such as setcchar, if opts is not a
null pointer, ncurses treats it as a pointer to int, and interprets
it instead of the short pair parameter as a color pair identifier.
• In functions that retrieve colors, such as getcchar, if opts is not
a null pointer, ncurses treats it as a pointer to int, and stores
the retrieved color pair identifier there as well as in the short
pair parameter (which may therefore undergo a narrowing conversion).
PORTABILITY
Applications employing ncurses extensions should condition their use on
the visibility of the NCURSES_VERSION preprocessor macro.
These functions are described in X/Open Curses Issue 4. It specifies no
error conditions for them.
X/Open Curses does not detail the layout of the cchar_t structure, de-
scribing only its minimal required contents:
• a spacing wide character (wchar_t),
• at least five non-spacing wide characters (wchar_t; see below),
• attributes (at least 15 bits' worth, inferred from the count of
specified WA_ constants),
• a color pair identifier (at least 16 bits, inferred from the short
type used to encode it).
Non-spacing characters are optional, in the sense that zero or more may
be stored in a cchar_t. XOpen/Curses specifies a limit:
Implementations may limit the number of non-spacing characters that
can be associated with a spacing character, provided any limit is at
least 5.
Then-contemporary Unix implementations adhered to that limit.
• AIX 4 and OSF/1 4 used the same declaration with a single spacing
wide character c and an array of 5 non-spacing wide characters z.
• HP-UX 10 used an opaque structure of 28 bytes, large enough for 6
wchar_t values.
• Solaris xcurses uses a single array of 6 wchar_t values.
ncurses defined its cchar_t in 1995 using 5 as the total of spacing and
non-spacing characters (CCHARW_MAX). That was probably due to a mis-
reading 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.
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 curses implementation). Unicode does not limit the (analogous) num-
ber of combining characters in a grapheme cluster; some applications may
be affected. ncurses can be compiled with a different CCHARW_MAX value;
doing so alters the library's ABI.
HISTORY
X/Open Curses Issue 4 (1995) initially specified these functions.
SEE ALSO
ncurses(3NCURSES), attr(3NCURSES), color(3NCURSES), wcwidth(3)
ncurses 6.5 2025-02-01 getcchar(3NCURSES)
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