Ubuntu Manpage: getcchar, setcchar - Get a wide character string and rendition from a cchar

Provided by: ncurses-doc_6.2-0ubuntu2.1_all

NAME

       getcchar,  setcchar  -  Get  a wide character string and rendition from a cchar_t or set a
       cchar_t from a wide-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 nonspacing characters may follow.  Additional nonspacing characters
           are ignored.

           The string may  contain  a  single  control  character  instead.   In  that  case,  no
           nonspacing characters are allowed.

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.

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.

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.

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.