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

Provided by: ncurses-doc_6.4+20240113-1ubuntu2_all

NAME

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

SYNOPSIS

       #include <curses.h>

       int getcchar(
               const cchar_t *wcval,
               wchar_t *wch,
               attr_t *attrs,
               short *color_pair,
               void *opts );

       int setcchar(
               cchar_t *wcval,
               const wchar_t *wch,
               const attr_t attrs,
               short color_pair,
               const void *opts );

DESCRIPTION

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

       •   Extracts information from a cchar_t value wcval

       •   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 wcval, into the array pointed to by wch.

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

       •   Obtains the number of wide characters pointed to by wcval

       •   Does not change the data referenced by attrs or color_pair

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

       •   The character attributes in attrs

       •   The color pair in color_pair

       •   The wide-character string pointed to by wch.  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.

RETURN VALUE

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

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

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

NOTES

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

EXTENSIONS

       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.

PORTABILITY

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.