curs_add_wch - add a curses complex character to a window and advance the cursor

NAME SYNOPSIS DESCRIPTION add_wch echo_wchar Line Graphics RETURN VALUE NOTES PORTABILITY WACS Symbols Complex Characters SEE ALSO

NAME

add_wch, wadd_wch, mvadd_wch, mvwadd_wch, echo_wchar, wecho_wchar − add a curses complex character to a window and advance the cursor

int add_wch(const cchar_t *wch);
int wadd_wch(WINDOW *win, const cchar_t *wch);
int mvadd_wch(int y, int x, const cchar_t *wch);
int mvwadd_wch(WINDOW *win, int y, int x, const cchar_t *wch);

int echo_wchar(const cchar_t *wch);
int wecho_wchar(WINDOW *win, const cchar_t *wch);

DESCRIPTION

add_wch

The add_wch, wadd_wch, mvadd_wch, and mvwadd_wch functions put the complex character wch into the given window at its current position, which is then advanced. These functions perform wrapping and special-character processing as follows:

•

If wch refers to a spacing character, then any previous character at that location is removed. A new character specified by wch is placed at that location with rendition specified by wch. The cursor then advances after this spacing character, to prepare for writing the next character on the screen.

The newly added spacing character is the base of the active complex character. Subsequent non-spacing characters can be combined with this base until another spacing character is written to the screen, or the cursor is moved, e.g., using wmove.

•

If wch refers to a non-spacing character, it is appended to the active complex character, retaining the previous characters at that location. The rendition specified by wch is ignored.

The cursor is not advanced after adding a non-spacing character. Subsequent calls to add non-spacing characters will update the same position.

•

If the character part of wch is a tab, newline, backspace or other control character, the window is updated and the cursor moves as if addch were called.

echo_wchar

The echo_wchar function is functionally equivalent to a call to add_wch followed by a call to refresh(3X). Similarly, the wecho_wchar is functionally equivalent to a call to wadd_wch followed by a call to wrefresh. The knowledge that only a single character is being output is taken into consideration and, for non-control characters, a considerable performance gain might be seen by using the *echo* functions instead of their equivalents.

Line Graphics

Like addch(3X), addch_wch accepts symbols which make it simple to draw lines and other frequently used special characters. These symbols correspond to the same VT100 line-drawing set as addch(3X).

The wide-character configuration of ncurses also defines symbols for thick lines (acsc “J” to “V”):

and for double-lines (acsc “A” to “I”):

Unicode’s descriptions for these characters differs slightly from ncurses, by introducing the term “light” (along with less important details). Here are its descriptions for the normal, thick, and double horizontal lines:

	•		U+2500 BOX DRAWINGS LIGHT HORIZONTAL
	•		U+2501 BOX DRAWINGS HEAVY HORIZONTAL
	•		U+2550 BOX DRAWINGS DOUBLE HORIZONTAL

RETURN VALUE

All routines return the integer ERR upon failure and OK on success.

X/Open does not define any error conditions. This implementation returns an error

	•		if the window pointer is null or
	•		if it is not possible to add a complete character in the window.

The latter may be due to different causes:

	•		If scrollok(3X) is not enabled, writing a character at the lower right margin succeeds. However, an error is returned because it is not possible to wrap to a new line
	•		If an error is detected when converting a multibyte character to a sequence of bytes, or if it is not possible to add all of the resulting bytes in the window, an error is returned.

Functions with a “mv” prefix first perform a cursor movement using wmove, and return an error if the position is outside the window, or if the window pointer is null.

NOTES

Note that add_wch, mvadd_wch, mvwadd_wch, and echo_wchar may be macros.

PORTABILITY

These functions are described in the XSI Curses standard, Issue 4. The defaults specified for line-drawing characters apply in the POSIX locale.

WACS Symbols

X/Open Curses makes it clear that the WACS_ symbols should be defined as a pointer to cchar_t data, e.g., in the discussion of border_set. A few implementations are problematic:

	•		NetBSD curses defines the symbols as a wchar_t within a cchar_t.
	•		HP-UX curses equates some of the ACS_ symbols to the analogous WACS_ symbols as if the ACS_ symbols were wide characters. The misdefined symbols are the arrows and other symbols which are not used for line-drawing.

X/Open Curses does not define symbols for thick- or double-lines. SVr4 curses implementations defined their line-drawing symbols in terms of intermediate symbols. This implementation extends those symbols, providing new definitions which are not in the SVr4 implementations.

Not all Unicode-capable terminals provide support for VT100-style alternate character sets (i.e., the acsc capability), with their corresponding line-drawing characters. X/Open Curses did not address the aspect of integrating Unicode with line-drawing characters. Existing implementations of Unix curses (AIX, HP-UX, Solaris) use only the acsc character-mapping to provide this feature. As a result, those implementations can only use single-byte line-drawing characters. Ncurses 5.3 (2002) provided a table of Unicode values to solve these problems. NetBSD curses incorporated that table in 2010.

In this implementation, the Unicode values are used instead of the terminal description’s acsc mapping as discussed in ncurses(3X) for the environment variable NCURSES_NO_UTF8_ACS. In contrast, for the same cases, the line-drawing characters described in curs_addch(3X) will use only the ASCII default values.

Having Unicode available does not solve all of the problems with line-drawing for curses:

	•		The closest Unicode equivalents to the VT100 graphics S1, S3, S7 and S9 frequently are not displayed at the regular intervals which the terminal used.
	•		The lantern is a special case. It originated with the AT&T 4410 terminal in the early 1980s. There is no accessible documentation depicting the lantern symbol on the AT&T terminal.

Lacking documentation, most readers assume that a storm lantern was intended. But there are several possibilities, all with problems.

Unicode 6.0 (2010) does provide two lantern symbols: U+1F383 and U+1F3EE. Those were not available in 2002, and are irrelevant since they lie outside the BMP and as a result are not generally available in terminals. They are not storm lanterns, in any case.

Most storm lanterns have a tapering glass chimney (to guard against tipping); some have a wire grid protecting the chimney.

For the tapering appearance, ☃ U+2603 was adequate. In use on a terminal, no one can tell what the image represents. Unicode calls it a snowman.

Others have suggested these alternatives: § U+00A7 (section mark), Θ U+0398 (theta), Φ U+03A6 (phi), δ U+03B4 (delta), ⌧ U+2327 (x in a rectangle), ╬ U+256C (forms double vertical and horizontal), and ☒ U+2612 (ballot box with x).

Complex Characters

The complex character type cchar_t can store more than one wide character (wchar_t). The X/Open Curses description does not mention this possibility, describing only the cases where wch is a spacing character or a non-spacing character.

This implementation assumes that wch is constructed using setcchar(3X), and in turn that the result

	•		contains at most one spacing character in the beginning of its list of wide characters, and zero or more non-spacing characters or
	•		may hold one non-spacing character.

In the latter case, ncurses adds the non-spacing character to the active (base) spacing character.