curs_getcchar.3x - Man Page

#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);

The curses complex character data type cchar_t is a structure type comprising 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.

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.

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.

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).

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, describing 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:

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 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.

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) number 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.

These functions were initially specified by X/Open Curses Issue 4 (1995).

curses(3X), curs_attr(3X), curs_color(3X), wcwidth(3)

The man pages getcchar.3x(3), gettchar.3x(3), setcchar.3x(3) and settchar.3x(3) are aliases of curs_getcchar.3x(3).