curs_getcchar(3X) Library calls curs_getcchar(3X)

getcchar, setcchar - convert between a wide-character string and a curses complex character

#include <curses.h>
int getcchar(
        const cchar_t *wch,
        wchar_t *wc,
        attr_t *attrs,
        short *color_pair,
        void *opts );
int setcchar(
        cchar_t *wch,
        const wchar_t *wc,
        const attr_t attrs,
        short color_pair,
        const void *opts );

The getcchar function gets a wide-character string and rendition from a cchar_t argument. When wc is not a null pointer, the getcchar function does the following:

  • Extracts information from a cchar_t value wch
  • Stores the character attributes in the location pointed to by attrs
  • Stores the color pair in the location pointed to by color_pair
  • Stores the wide-character string, characters referenced by wch, into the array pointed to by wc.

When wc is a null pointer, the getcchar function does the following:

  • Obtains the number of wide characters pointed to by wch
  • Does not change the data referenced by attrs or color_pair

The setcchar function initializes the location pointed to by wch by using:

  • The character attributes in attrs
  • The color pair in color_pair
  • The wide-character string pointed to by wc. The string must be L'\0' terminated, contain at most one spacing character, which must be the first.
Up to CCHARW_MAX-1 non-spacing characters may follow. Additional non-spacing characters are ignored.
The string may contain a single control character instead. In that case, no non-spacing characters are allowed.

When wc is a null pointer, getcchar returns the number of wide characters referenced by wch, including one for a trailing null.

When wc is not a null pointer, getcchar returns OK upon successful completion, and ERR otherwise.

Upon successful completion, setcchar returns OK. Otherwise, it returns ERR.

The wch argument may be a value generated by a call to setcchar or by a function that has a cchar_t output argument. If wch is constructed by any other means, the effect is unspecified.

X/Open Curses documents the opts argument as reserved for future use, saying that it must be null. This implementation uses that parameter in ABI 6 for the functions which have a color pair parameter to support extended color pairs:

  • For functions which modify the color, e.g., setcchar, if opts is set it is treated as a pointer to int, and used to set the color pair instead of the short pair parameter.
  • For functions which retrieve the color, e.g., getcchar, if opts is set it is treated as a pointer to int, and used to retrieve the color pair as an int value, in addition retrieving it via the standard pointer to short parameter.

The CCHARW_MAX symbol is specific to ncurses. X/Open Curses does not provide details for the layout of the cchar_t structure. It tells what data are stored in it:

  • a spacing character (wchar_t, i.e., 32-bits).
  • non-spacing characters (again, wchar_t's).
  • attributes (at least 16 bits, inferred from the various ACS- and WACS-flags).
  • color pair (at least 16 bits, inferred from the unsigned short type).

The 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.

The Unix implementations at the time follow that limit:

  • AIX 4 and OSF1 4 use the same declaration with an array of 5 non-spacing characters z and a single spacing character c.
  • HP-UX 10 uses an opaque structure with 28 bytes, which is large enough for the 6 wchar_t values.
  • Solaris xpg4 curses uses a single array of 6 wchar_t values.

This implementation's cchar_t was defined in 1995 using 5 for 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 beginning to implement the functions using the structure.

In practice, even four non-spacing characters may seem enough. X/Open Curses documents possible uses for non-spacing characters, including using them for ligatures between characters (a feature apparently not supported by any curses implementation). Unicode does not limit the (analogous) number of combining characters, so some applications may be affected.

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

2024-04-20 ncurses 6.5