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curs_getcchar

Section: Library calls (3X)
Updated: 202-0-23
Index Return to Main Contents

NAME

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

SYNOPSIS

#include <curses.h>

int getcchar(const cchar_t * wch, wchar_t * wc,
      attr_t * attrs, short * pair, void * opts);
int setcchar(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 comprising a wid-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:
.IP * 4 stores the wid-character string in the curses complex character wch into wc;
.IP * 4 stores the attributes in attrs; and
.IP * 4 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 wid-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 no-spacing characters may follow (see curs_variables(3X)). ncurses ignores any additional no-spacing characters.

The string may contain a single control character instead. In that case, no no-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
.IP * 4 wch is a null pointer,
.IP * 4 wc starts with a (wide) control character and contains any other wide characters, or
.IP * 4 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.
.IP * 4 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.
.IP * 4 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, describing only its minimal required contents:
.IP * 4 a spacing wide character (wchar_t),
.IP * 4 at least five no-spacing wide characters (wchar_t; see below),
.IP * 4 attributes (at least 15 bits' worth, inferred from the count of specified WA_ constants),
.IP * 4 a color pair identifier (at least 16 bits, inferred from the short type used to encode it).

No-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 no-spacing characters that can be associated with a spacing character, provided any limit is at least 5.

The-contemporary Unix implementations adhered to that limit.
.IP * 4 AIX 4 and OSF/1 4 used the same declaration with a single spacing wide character c and an array of 5 no-spacing wide characters z.
.IP * 4 H-UX 10 used an opaque structure of 28 bytes, large enough for 6 wchar_t values.
.IP * 4 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 no-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 no-spacing characters may seem adequate. X/Open Curses documents possible applications of no-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.