curs_add_wch(3X)

NAME
add_wch, wadd_wch, mvadd_wch, mvwadd_wch, echo_wchar, wecho_wchar - add a curses complex character to a window, possibly advancing the cursor

SYNOPSIS
#include <curses.h>

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

  wadd_wch
wadd_wch writes the complex character wch to the window win, then may advance the cursor position, analogously to the standard C library's putwchar(3). ncurses(3X) describes the variants of this function.

Much behavior depends on whether the wide characters in wch are spacing or non-spacing; see subsection “Complex Characters” below. If wch contains a spacing character, then any character at the cursor is first removed. The complex character wch, with its attributes and color pair identifier, becomes the base of the active complex character. If wch contains only non-spacing characters, they are combined with the active complex character. curses ignores its attributes and color pair identifier, and does not advance the cursor.

Further non-spacing characters added with wadd_wch are not written at the new cursor position but combine with the active complex character until another spacing character is written to the window or the cursor is moved.

If advancement occurs at the right margin, the cursor automatically wraps to the beginning of the next line, then, if it was at the bottom of the scrolling region, and if scrollok(3X) is enabled for win, the scrolling region scrolls up one line.

If wch is a backspace, carriage return, line feed, or tab, the cursor moves appropriately within the window. Backspace moves the cursor one character left; at the left margin of a window, it does nothing. Carriage return moves the cursor to the left margin on the same line of the window. Line feed does a clrtoeol(3X), then advances as if from the right margin. Tab advances the cursor to the next tab stop (possibly on the next line); these are placed at every eighth column by default. Alter the tab interval with the TABSIZE extension; see curs_variables(3X).

If wch is any other nonprintable character, it is drawn in printable form using the same convention as wunctrl(3X). Calling win_wch(3X) on the location of a nonprintable character does not return the character itself, but its wunctrl(3X) representation.

A cchar_t can be copied from place to place using win_wch(3X) and wadd_wch.

  wecho_wchar
echo_wchar and wecho_wchar are equivalent to calling (w)add_wch followed by (w)refresh. curses interprets these functions as a hint that only a single (complex) character is being output; for non-control characters, a considerable performance gain may be enjoyed by employing them.

  Forms-Drawing Characters
curses defines macros starting with WACS_ that can be used with wadd_wch to write line-drawing and other special characters to the screen. ncurses terms these forms-drawing characters. The ACS default listed below is used if the acs_chars (acsc) terminfo capability does not define a terminal-specific replacement for it, or if the terminal and locale configuration requires Unicode to access these characters but the library is unable to use Unicode. The “acsc char” column corresponds to how the characters are specified in the acs_chars (acsc) string capability, and the characters in it may appear on the screen if the terminal type's database entry incorrectly advertises ACS support. The name “ACS” originates in the Alternate Character Set feature of the DEC VT100 terminal.

 | Unicode | ACS | acsc |
Symbol | Default | Default | char | Glyph Name
WACS_BLOCK | 0x25ae | # | 0 | solid square block
WACS_BOARD | 0x2592 | # | h | board of squares
WACS_BTEE | 0x2534 | + | v | bottom tee
WACS_BULLET | 0x00b7 | o | ~ | bullet
WACS_CKBOARD | 0x2592 | : | a | checker board (stipple)
WACS_DARROW | 0x2193 | v | . | arrow pointing down
WACS_DEGREE | 0x00b0 | ' | f | degree symbol
WACS_DIAMOND | 0x25c6 | + | ` | diamond
WACS_GEQUAL | 0x2265 | > | > | greater-than-or-equal-to
WACS_HLINE | 0x2500 | - | q | horizontal line
WACS_LANTERN | 0x2603 | # | i | lantern symbol
WACS_LARROW | 0x2190 | < | , | arrow pointing left
WACS_LEQUAL | 0x2264 | < | y | less-than-or-equal-to
WACS_LLCORNER | 0x2514 | + | m | lower left-hand corner
WACS_LRCORNER | 0x2518 | + | j | lower right-hand corner
WACS_LTEE | 0x2524 | + | t | left tee
WACS_NEQUAL | 0x2260 | ! | | | not-equal
WACS_PI | 0x03c0 | * | { | greek pi
WACS_PLMINUS | 0x00b1 | # | g | plus/minus
WACS_PLUS | 0x253c | + | n | plus
WACS_RARROW | 0x2192 | > | + | arrow pointing right
WACS_RTEE | 0x251c | + | u | right tee
WACS_S1 | 0x23ba | - | o | scan line 1
WACS_S3 | 0x23bb | - | p | scan line 3
WACS_S7 | 0x23bc | - | r | scan line 7
WACS_S9 | 0x23bd |  | s | scan line 9
WACS_STERLING | 0x00a3 | f | } | pound-sterling symbol
WACS_TTEE | 0x252c | + | w | top tee
WACS_UARROW | 0x2191 | ^ | - | arrow pointing up
WACS_ULCORNER | 0x250c | + | l | upper left-hand corner
WACS_URCORNER | 0x2510 | + | k | upper right-hand corner
WACS_VLINE | 0x2502 | | | x | vertical line

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

 | Unicode | ASCII | acsc |
ACS Name | Default | Default | Char | Glyph Name
WACS_T_BTEE | 0x253b | + | V | thick tee pointing up
WACS_T_HLINE | 0x2501 | - | Q | thick horizontal line
WACS_T_LLCORNER | 0x2517 | + | M | thick lower left corner
WACS_T_LRCORNER | 0x251b | + | J | thick lower right corner
WACS_T_LTEE | 0x252b | + | T | thick tee pointing right
WACS_T_PLUS | 0x254b | + | N | thick large plus
WACS_T_RTEE | 0x2523 | + | U | thick tee pointing left
WACS_T_TTEE | 0x2533 | + | W | thick tee pointing down
WACS_T_ULCORNER | 0x250f | + | L | thick upper left corner
WACS_T_URCORNER | 0x2513 | + | K | thick upper right corner
WACS_T_VLINE | 0x2503 | | | X | thick vertical line

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

 | Unicode | ASCII | acsc |
ACS Name | Default | Default | Char | Glyph Name
WACS_D_BTEE | 0x2569 | + | H | double tee pointing up
WACS_D_HLINE | 0x2550 | - | R | double horizontal line
WACS_D_LLCORNER | 0x255a | + | D | double lower left corner
WACS_D_LRCORNER | 0x255d | + | A | double lower right corner
WACS_D_LTEE | 0x2560 | + | F | double tee pointing right
WACS_D_PLUS | 0x256c | + | E | double large plus
WACS_D_RTEE | 0x2563 | + | G | double tee pointing left
WACS_D_TTEE | 0x2566 | + | I | double tee pointing down
WACS_D_ULCORNER | 0x2554 | + | C | double upper left corner
WACS_D_URCORNER | 0x2557 | + | B | double upper right corner
WACS_D_VLINE | 0x2551 | | | Y | double vertical line

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
These functions return OK on success and ERR on failure. In ncurses, wadd_wch returns ERR if win is NULL, wrapping to a new line is impossible because scrollok(3X) has not been called on win when writing to its bottom right location is attempted, or it is not possible to add a complete character at the cursor position.

Functions prefixed with “mv” first perform cursor movement and fail if the position (y, x) is outside the window boundaries.

NOTES
add_wch, mvadd_wch, mvwadd_wch, and echo_wchar may be implemented as macros.

EXTENSIONS

  TABSIZE
The TABSIZE variable is implemented in SVr4 and other versions of curses, but is not specified by X/Open Curses (see curs_variables(3X)).

PORTABILITY
These functions are described in X/Open Curses, Issue 4. It specifies no error conditions for them.

The defaults specified for forms-drawing characters apply in the POSIX locale. 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 specify 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 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). X/Open Curses does not mention this possibility, specifying behavior only where wch is a single character, either spacing or non-spacing.

ncurses assumes that wch is constructed using setcchar(3X), and in turn that the result contains at most one spacing character at the beginning of its list of wide characters, and zero or more non-spacing characters, or holds one non-spacing character.

In the latter case, ncurses adds the non-spacing character to the active complex character.

HISTORY
These functions were initially specified by X/Open Curses, Issue 4. The System V Interface Definition, Version 4 (1995), specified functions named waddwch and wechowchar (and the usual variants). These were later additions to SVr4.x, not appearing in the first SVr4 (1989). They differed from X/Open's later wadd_wch and wecho_wchar in that they each took an argument of type wchar_t instead of cchar_t.

SEE ALSO
curs_addch(3X) describes comparable functions of the ncurses library in its non-wide-character configuration.

curses(3X), curs_addwstr(3X), curs_add_wchstr(3X), curs_attr(3X), curs_clear(3X), curs_getcchar(3X), curs_outopts(3X), curs_refresh(3X), curs_variables(3X), putwc(3)