add_wch(3NCURSES)

add_wch 💖 (3NCURSES) — library calls

okay bestie, gather round, because this one is a whole vibe 🫶. We're in curses.h territory, we're doing complex characters, and yes we're possibly moving the cursor while we do it. no cap.

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✨ NAME ✨

add_wch, wadd_wch, mvadd_wch, mvwadd_wch, echo_wchar, wecho_wchar — drop a curses complex character into a window, and possibly scoot the cursor along like the little main character it is 🎀

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🌸 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);

/* (integer) constants */
/* ... */ WACS_BLOCK;
/* ... */ WACS_BOARD;
/* ... */ WACS_BTEE;
/* ... */ WACS_BULLET;
/* ... */ WACS_CKBOARD;
/* ... */ WACS_DARROW;
/* ... */ WACS_DEGREE;
/* ... */ WACS_DIAMOND;
/* ... */ WACS_HLINE;
/* ... */ WACS_LANTERN;
/* ... */ WACS_LARROW;
/* ... */ WACS_LLCORNER;
/* ... */ WACS_LRCORNER;
/* ... */ WACS_LTEE;
/* ... */ WACS_PLMINUS;
/* ... */ WACS_PLUS;
/* ... */ WACS_RARROW;
/* ... */ WACS_RTEE;
/* ... */ WACS_S1;
/* ... */ WACS_S9;
/* ... */ WACS_TTEE;
/* ... */ WACS_UARROW;
/* ... */ WACS_ULCORNER;
/* ... */ WACS_URCORNER;
/* ... */ WACS_VLINE;
/* extensions */
/* ... */ WACS_GEQUAL;
/* ... */ WACS_LEQUAL;
/* ... */ WACS_NEQUAL;
/* ... */ WACS_PI;
/* ... */ WACS_S3;
/* ... */ WACS_S7;
/* ... */ WACS_STERLING;
/* extensions for thick lines */
/* ... */ WACS_T_BTEE;
/* ... */ WACS_T_HLINE;
/* ... */ WACS_T_LLCORNER;
/* ... */ WACS_T_LRCORNER;
/* ... */ WACS_T_LTEE;
/* ... */ WACS_T_PLUS;
/* ... */ WACS_T_RTEE;
/* ... */ WACS_T_TTEE;
/* ... */ WACS_T_ULCORNER;
/* ... */ WACS_T_URCORNER;
/* ... */ WACS_T_VLINE;
/* extensions for double lines */
/* ... */ WACS_D_BTEE;
/* ... */ WACS_D_HLINE;
/* ... */ WACS_D_LLCORNER;
/* ... */ WACS_D_LRCORNER;
/* ... */ WACS_D_LTEE;
/* ... */ WACS_D_PLUS;
/* ... */ WACS_D_RTEE;
/* ... */ WACS_D_TTEE;
/* ... */ WACS_D_ULCORNER;
/* ... */ WACS_D_URCORNER;
/* ... */ WACS_D_VLINE;

🦋 fr fr, all of those WACS_* constants go in the synopsis like that, and every single one is staying right here where it belongs. We are not skipping a single line, bestie, not even one 💅

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that's the setup, the vibe check passed, and there is so much more coming — descriptions, options, return values, the whole little saga 🌈. hold on tight 🧚

🌈 DESCRIPTION (part 2, bestie we're still going) 🌈

💖 wadd_wch

Okay so wadd_wch writes the curses complex character wch to the window win, and then it may advance the cursor position — exactly analogously to how the standard C library's putwchar(3) does it. ncurses(3NCURSES) is where you go to read about the variants of this function, iykyk.

To build a curses complex character out of a wchar_t, you use setcchar(3NCURSES). And a cchar_t can be copied from place to place with win_wch(3NCURSES) and wadd_wch. curses defines constants to help you manipulate character attributes; peep attr(3NCURSES) for those. Also: a complex character whose only character component is a wide space, and whose only attribute is WA_NORMAL, is a blank character, which means it combines with the window's background character — see bkgrnd(3NCURSES) for that whole situation. ✨

Honestly so much of the behavior depends on whether the wide characters in wch are spacing or non-spacing; see the subsection “Complex Characters” below. But here's the tea:

• If wch contains a spacing character, then any character sitting at the cursor is first removed. The complex character wch, along with its attributes and color pair identifier, becomes the base of the active complex character.
• If wch contains only non-spacing characters, they get combined with the active complex character. curses ignores its attributes and color pair identifier, and does not advance the cursor.

And like, further non-spacing characters added with wadd_wch are not written at the new cursor position — they combine with the active complex character until another spacing character is written to the window, or until the cursor is moved. Periodt. 💅

If wch is a backspace, carriage return, line feed, or tab, the cursor moves appropriately within the window. Like:

• Backspace moves the cursor one character left; at the left margin of a window, it does absolutely nothing. tragic but true.
• Carriage return moves the cursor to the left margin on the same line of the window.
• Line feed does a clrtoeol(3NCURSES), 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.

Wanna change that tab interval? Use the TABSIZE extension; see curses_variables(3NCURSES). 🎀

If wch is any other nonprintable character, curses draws it in printable form using the same convention as wunctrl(3NCURSES). So heads up: calling win_wch(3NCURSES) on the location of a nonprintable character does not retrieve the character itself — you get its wunctrl(3NCURSES) representation instead. not me getting fooled by that 😭

Adding spacing characters with wadd_wch causes it to wrap at the right margin of the window:

• If the cursor is not at the bottom of the scrolling region and advancement occurs at the right margin, the cursor automatically wraps to the beginning of the next line. slay.
• If the cursor is at the bottom of the scrolling region when advancement occurs at the right margin, and scrollok(3NCURSES) is enabled for win, the scrolling region scrolls up one line and the cursor wraps as above. Otherwise, advancement and scrolling do not occur, and wadd_wch returns ERR. 💀

A window's margins may coincide with the screen boundaries. This may be a problem when ncurses updates the screen to match the curses window. When their right and bottom margins coincide, ncurses uses different strategies to handle the variations of scrolling and wrapping at the lower-right corner, depending on the terminal capabilities:

• If the terminal does not automatically wrap as characters are added at the right margin (i.e., auto right margins), ncurses writes the character directly.
• If the terminal has auto right margins, but also has capabilities for turning auto margins off and on, ncurses turns the auto margin feature off temporarily when writing to the lower-right corner.
• If the terminal has an insertion mode which can be turned off and on, ncurses writes the character just before the lower-right corner, and then inserts a character to push the update into the corner.

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🦋 wecho_wchar

echo_wchar and wecho_wchar are equivalent to calling (w)add_wch followed by (w)refresh on stdscr or the specified window. curses reads these functions as a hint that only a single (complex) character is being output — and for non-control characters, you may enjoy a considerable performance gain by employing them. the way that's literally free speed 👑

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🎀 Forms-Drawing Characters

curses defines macros starting with WACS_ that you can use with wadd_wch to write line-drawing and other symbols to the screen. ncurses calls these forms-drawing characters. curses uses the ACS default listed below when:

• the terminal type lacks the acs_chars (acsc) capability;
• that capability does not define a replacement for the character; or
• the terminal type and locale configuration require 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. Fun fact: the name “ACS” originates in the Alternate Character Set feature of the DEC VT100 terminal. ⭐

Here's the whole lineup, each one with its Unicode default, ACS default, acsc char, and glyph name:

• WACS_BLOCK — Unicode default U+25ae, ACS default #, acsc char 0, glyph name: solid square block
• WACS_BOARD — Unicode default U+2592, ACS default #, acsc char h, glyph name: board of squares
• WACS_BTEE — Unicode default U+2534, ACS default +, acsc char v, glyph name: bottom tee
• WACS_BULLET — Unicode default U+00b7, ACS default o, acsc char ~, glyph name: bullet
• WACS_CKBOARD — Unicode default U+2592, ACS default :, acsc char a, glyph name: checker board (stipple)
• WACS_DARROW — Unicode default U+2193, ACS default v, acsc char ., glyph name: arrow pointing down
• WACS_DEGREE — Unicode default U+00b0, ACS default ', acsc char f, glyph name: degree symbol
• WACS_DIAMOND — Unicode default U+25c6, ACS default +, acsc char `, glyph name: diamond
• WACS_GEQUAL — Unicode default U+2265, ACS default >, acsc char >, glyph name: greater-than-or-equal-to
• WACS_HLINE — Unicode default U+2500, ACS default -, acsc char q, glyph name: horizontal line
• WACS_LANTERN — Unicode default U+2603, ACS default #, acsc char i, glyph name: lantern symbol
• WACS_LARROW — Unicode default U+2190, ACS default <, acsc char ,, glyph name: arrow pointing left
• WACS_LEQUAL — Unicode default U+2264, ACS default <, acsc char y, glyph name: less-than-or-equal-to
• WACS_LLCORNER — Unicode default U+2514, ACS default +, acsc char m, glyph name: lower left-hand corner
• WACS_LRCORNER — Unicode default U+2518, ACS default +, acsc char j, glyph name: lower right-hand corner
• WACS_LTEE — Unicode default U+2524, ACS default +, acsc char t, glyph name: left tee
• WACS_NEQUAL — Unicode default U+2260, ACS default !, acsc char |, glyph name: not-equal
• WACS_PI — Unicode default U+03c0, ACS default *, acsc char {, glyph name: greek pi
• WACS_PLMINUS — Unicode default U+00b1, ACS default #, acsc char g, glyph name: plus/minus
• WACS_PLUS — Unicode default U+253c, ACS default +, acsc char n, glyph name: plus
• WACS_RARROW — Unicode default U+2192, ACS default >, acsc char +, glyph name: arrow pointing right
• WACS_RTEE — Unicode default U+251c, ACS default +, acsc char u, glyph name: right tee
• WACS_S1 — Unicode default U+23ba, ACS default -, acsc char o, glyph name: scan line 1
• WACS_S3 — Unicode default U+23bb, ACS default -, acsc char p, glyph name: scan line 3
• WACS_S7 — Unicode default U+23bc, ACS default -, acsc char r, glyph name: scan line 7
• WACS_S9 — Unicode default U+23bd, ACS default _, acsc char s, glyph name: scan line 9
• WACS_STERLING — Unicode default U+00a3, ACS default f, acsc char }, glyph name: pound-sterling symbol
• WACS_TTEE — Unicode default U+252c, ACS default +, acsc char w, glyph name: top tee
• WACS_UARROW — Unicode default U+2191, ACS default ^, acsc char -, glyph name: arrow pointing up
• WACS_ULCORNER — Unicode default U+250c, ACS default +, acsc char l, glyph name: upper left-hand corner
• WACS_URCORNER — Unicode default U+2510, ACS default +, acsc char k, glyph name: upper right-hand corner
• WACS_VLINE — Unicode default U+2502, ACS default |, acsc char x, glyph name: vertical line

The ncurses wide API also defines symbols for thick lines (acsc “J” through “N”, “T” through “X”, and “Q”):

• WACS_T_BTEE — Unicode default U+253b, ASCII default +, acsc char V, glyph name: thick tee pointing up
• WACS_T_HLINE — Unicode default U+2501, ASCII default -, acsc char Q, glyph name: thick horizontal line
• WACS_T_LLCORNER — Unicode default U+2517, ASCII default +, acsc char M, glyph name: thick lower left corner
• WACS_T_LRCORNER — Unicode default U+251b, ASCII default +, acsc char J, glyph name: thick lower right corner
• WACS_T_LTEE — Unicode default U+252b, ASCII default +, acsc char T, glyph name: thick tee pointing right
• WACS_T_PLUS — Unicode default U+254b, ASCII default +, acsc char N, glyph name: thick large plus
• WACS_T_RTEE — Unicode default U+2523, ASCII default +, acsc char U, glyph name: thick tee pointing left
• WACS_T_TTEE — Unicode default U+2533, ASCII default +, acsc char W, glyph name: thick tee pointing down
• WACS_T_ULCORNER — Unicode default U+250f, ASCII default +, acsc char L, glyph name: thick upper left corner
• WACS_T_URCORNER — Unicode default U+2513, ASCII default +, acsc char K, glyph name: thick upper right corner
• WACS_T_VLINE — Unicode default U+2503, ASCII default |, acsc char X, glyph name: thick vertical line

…and for double lines (acsc “A” through “I”, plus “R” and “Y”):

• WACS_D_BTEE — Unicode default U+2569, ASCII default +, acsc char H, glyph name: double tee pointing up
• WACS_D_HLINE — Unicode default U+2550, ASCII default -, acsc char R, glyph name: double horizontal line
• WACS_D_LLCORNER — Unicode default U+255a, ASCII default +, acsc char D, glyph name: double lower left corner
• WACS_D_LRCORNER — Unicode default U+255d, ASCII default +, acsc char A, glyph name: double lower right corner
• WACS_D_LTEE — Unicode default U+2560, ASCII default +, acsc char F, glyph name: double tee pointing right
• WACS_D_PLUS — Unicode default U+256c, ASCII default +, acsc char E, glyph name: double large plus
• WACS_D_RTEE — Unicode default U+2563, ASCII default +, acsc char G, glyph name: double tee pointing left
• WACS_D_TTEE — Unicode default U+2566, ASCII default +, acsc char I, glyph name: double tee pointing down
• WACS_D_ULCORNER — Unicode default U+2554, ASCII default +, acsc char C, glyph name: double upper left corner
• WACS_D_URCORNER — Unicode default U+2557, ASCII default +, acsc char B, glyph name: double upper right corner
• WACS_D_VLINE — Unicode default U+2551, ASCII default |, acsc char Y, glyph name: 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

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✨ RETURN VALUE ✨

These functions return OK on success and ERR on failure. simple as that 🫶

In ncurses, these functions fail if:

• the curses screen has not been initialized,
• (for functions taking a WINDOW pointer argument) win is a null pointer,
• wrapping to a new line is impossible because scrollok(3NCURSES) has not been called on win (or stdscr, as applicable) 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. like, boundaries are boundaries bestie 🚫

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💜 NOTES

add_wch, mvadd_wch, mvwadd_wch, and echo_wchar may be implemented as macros. yes, macros — so don't go taking their address like it's nothing 🙈

💫 EXTENSIONS 💫

Okay bestie, so these symbols — WACS_S3, WACS_S7, WACS_LEQUAL, WACS_GEQUAL, WACS_PI, WACS_NEQUAL, and WACS_STERLING — are not standard. Not even a little. But here's the tea: soooo many publicly available terminfo entries ship with acs_chars (acsc) capabilities that literally have their key characters (pryz{|}) baked right in, and a second-hand list of their character descriptions came to light. So the ncurses devs just went ahead and invented WACS-prefixed names for them. Iconic behaviour honestly. 💅

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🌍 PORTABILITY 🌍

If your app is using ncurses extensions, you gotta gate that usage on whether the NCURSES_VERSION preprocessor macro is even visible. No macro, no party. 🎀

These functions are described in X/Open Curses Issue 4. And guess what it specifies for error conditions? Absolutely nothing. It says no error conditions. Cool cool cool.

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 — like, they literally say it in the discussion of border_set. But a few implementations are out here being 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. ncurses extends those symbols, providing new definitions not found in SVr4 implementations. We love an upgrade. ✨

Not all Unicode-capable terminals provide support for VT100-style alternate character sets (i.e., the acsc_chars (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 System V curses (AIX, HP-UX, Solaris) use only the acsc_chars (acsc) character-mapping to provide this feature. As a result, those implementations can use only 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. 🫶

ncurses uses the Unicode values instead of the terminal type description's acsc_chars (acsc) mapping as discussed in ncurses(3NCURSES) for the environment variable NCURSES_NO_UTF8_ACS. In contrast, for the same cases, the line-drawing characters described in addch(3NCURSES) will use only the ASCII default values.

Having Unicode available does not solve all of the problems with line-drawing for curses. Bestie, it's giving "we tried":

• 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 Basic Multilingual Plane and as a result are unavailable on many 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(3NCURSES), 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. Slay. 🔥

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📜 HISTORY 📜

X/Open Curses Issue 4 (1995) initially specified these functions. The System V Interface Definition (SVID) Version 4 of the same year specified functions named waddwch (and the usual variants), echowchar, and wechowchar. 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. SVID defined no WACS_ symbols. 💀

X/Open Curses Issue 4 also defined many of the WACS_ constants, excepting WACS_GEQUAL, WACS_LEQUAL, WACS_NEQUAL, WACS_PI, WACS_S3, WACS_S7, and WACS_STERLING; and those for drawing thick and double lines.

ncurses 5.3 (2002) furnished the remaining WACS_ constants. The glow-up was real. 👑

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👀 SEE ALSO 👀

• addch(3NCURSES) describes comparable functions of the ncurses library in its non-wide-character configuration.
• ncurses(3NCURSES), addwstr(3NCURSES), add_wchstr(3NCURSES), attr(3NCURSES), bkgrnd(3NCURSES), clear(3NCURSES), getcchar(3NCURSES), outopts(3NCURSES), refresh(3NCURSES), curses_variables(3NCURSES), putwc(3)

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And that's a wrap on add_wch(3NCURSES), bestie! This lil masterpiece came to you courtesy of ncurses 6.6, dated 2025-11-11. Go forth and draw them lines. 🦋✨💖