--- name: "addch" section: "3ncurses" platform: "linux" package: "ncurses-doc" version: "6.5+20250216-2" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/addch/3ncurses" --- # addch(3ncurses) add a curses character to a window and advance the cursor ## NAME **addch**, **waddch**, **mvaddch**, **mvwaddch**, **echochar**, **wechochar** - add a *curses* character to a window and advance the cursor ## SYNOPSIS ``` #include ``` **int addch(const chtype** *ch***);** **int waddch(WINDOW \****win***, const chtype** *ch***);** **int mvaddch(int** *y***, int** *x***, const chtype** *ch***);** **int mvwaddch(WINDOW \****win***, int** *y***, int** *x***, const chtype** *ch***);** **int echochar(const chtype** *ch***);** **int wechochar(WINDOW \****win***, const chtype** *ch***);** */\* (integer) constants \*/* **/\*** *... \*/* **ACS\_BLOCK;** /\* *... \*/* **ACS\_BOARD;** /\* *... \*/* **ACS\_BTEE;** /\* *... \*/* **ACS\_BULLET;** /\* *... \*/* **ACS\_CKBOARD;** /\* *... \*/* **ACS\_DARROW;** /\* *... \*/* **ACS\_DEGREE;** /\* *... \*/* **ACS\_DIAMOND;** /\* *... \*/* **ACS\_HLINE;** /\* *... \*/* **ACS\_LANTERN;** /\* *... \*/* **ACS\_LARROW;** /\* *... \*/* **ACS\_LLCORNER;** /\* *... \*/* **ACS\_LRCORNER;** /\* *... \*/* **ACS\_LTEE;** /\* *... \*/* **ACS\_PLMINUS;** /\* *... \*/* **ACS\_PLUS;** /\* *... \*/* **ACS\_RARROW;** /\* *... \*/* **ACS\_RTEE;** /\* *... \*/* **ACS\_S1;** /\* *... \*/* **ACS\_S9;** /\* *... \*/* **ACS\_TTEE;** /\* *... \*/* **ACS\_UARROW;** /\* *... \*/* **ACS\_ULCORNER;** /\* *... \*/* **ACS\_URCORNER;** /\* *... \*/* **ACS\_VLINE;** */\* extensions \*/* /\* *... \*/* **ACS\_GEQUAL;** /\* *... \*/* **ACS\_LEQUAL;** /\* *... \*/* **ACS\_NEQUAL;** /\* *... \*/* **ACS\_PI;** /\* *... \*/* **ACS\_S3;** /\* *... \*/* **ACS\_S7;** /\* *... \*/* **ACS\_STERLING;** ## DESCRIPTION ### waddch **waddch** writes the *curses* character *ch* to the window *win*, then advances the cursor position, analogously to the standard C library's [*putchar*(3)](/putchar/3.md). **ncurses**(3NCURSES) describes the variants of this function. Construct a *curses* character from a *char* by assignment. Subsection “Video Attributes” of **attron**(3NCURSES) describes how to manipulate its attributes and color pair. (A color pair selection is not honored unless initialized; see **start\_color**(3NCURSES).) 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**(3NCURSES) is enabled for *win*, the scrolling region scrolls up one line. If *ch* 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**(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. Alter the tab interval with the **TABSIZE** extension; see **curses\_variables**(3NCURSES). If *ch* is any other nonprintable character, it is drawn in printable form using the same convention as **unctrl**(3NCURSES). Calling **winch**(3NCURSES) on the location of a nonprintable character does not return the character itself, but its **unctrl**(3NCURSES) representation. The object or expression *ch* may contain attributes and/or a color pair identifier. (A *chtype* can be copied from place to place using **winch**(3NCURSES) and **waddch**.) See **attr**(3NCURSES) for values of predefined constants that can be usefully “or”ed with characters. A *ch* whose character component is a space, and whose only attribute is **A\_NORMAL**, is a *blank character*, and therefore combines with the background character; see **bkgd**(3NCURSES). ### wechochar **echochar** and **wechochar** are equivalent to calling (**w**)**addch** followed by (**w**)**refresh** on **stdscr** or the specified window. *curses* interprets these functions as a hint to its optimizer that only a single character cell in the window is being altered between refreshes; for non-control characters, a considerable performance gain may be enjoyed by employing them. ### Forms-Drawing Characters *curses* defines macros starting with **ACS\_** that can be used with **waddch** to write line-drawing and other symbols 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. | | | | | | --- | --- | --- | --- | | | **ACS** | **acsc** | | | **Symbol** | **Default** | **char** | **Glyph Name** | | **ACS\_BLOCK** | # | 0 | solid square block | | **ACS\_BOARD** | # | h | board of squares | | **ACS\_BTEE** | + | v | bottom tee | | **ACS\_BULLET** | o | ~ | bullet | | **ACS\_CKBOARD** | : | a | checker board (stipple) | | **ACS\_DARROW** | v | | arrow pointing down | | **ACS\_DEGREE** | ' | f | degree symbol | | **ACS\_DIAMOND** | + | \` | diamond | | **ACS\_GEQUAL** | \> | \> | greater-than-or-equal-to | | **ACS\_HLINE** | - | q | horizontal line | | **ACS\_LANTERN** | # | i | lantern symbol | | **ACS\_LARROW** | \< | , | arrow pointing left | | **ACS\_LEQUAL** | \< | y | less-than-or-equal-to | | **ACS\_LLCORNER** | + | m | lower left-hand corner | | **ACS\_LRCORNER** | + | j | lower right-hand corner | | **ACS\_LTEE** | + | t | left tee | | **ACS\_NEQUAL** | ! | \| | not-equal | | **ACS\_PI** | \* | { | greek pi | | **ACS\_PLMINUS** | # | g | plus/minus | | **ACS\_PLUS** | + | n | plus | | **ACS\_RARROW** | \> | + | arrow pointing right | | **ACS\_RTEE** | + | u | right tee | | **ACS\_S1** | - | o | scan line 1 | | **ACS\_S3** | - | p | scan line 3 | | **ACS\_S7** | - | r | scan line 7 | | **ACS\_S9** | \_ | s | scan line 9 | | **ACS\_STERLING** | f | } | pound-sterling symbol | | **ACS\_TTEE** | + | w | top tee | | **ACS\_UARROW** | ^ | - | arrow pointing up | | **ACS\_ULCORNER** | + | l | upper left-hand corner | | **ACS\_URCORNER** | + | k | upper right-hand corner | | **ACS\_VLINE** | \| | x | vertical line | ## RETURN VALUE These functions return **OK** on success and **ERR** on failure. In *ncurses*, **waddch** and **wechochar** return **ERR** 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 a write to its bottom right location is attempted, or - • it is not possible to add a complete character at the cursor position. The last may be due to different causes: - • conversion of a wide character to a multibyte character sequence can fail, or - • at least one of the bytes resulting from wide character conversion to a multibyte character sequence cannot be added to the window. See section “PORTABILITY” below regarding the use of **waddch** with wide characters. Functions prefixed with “mv” first perform cursor movement and fail if the position (*y*, *x*) is outside the window boundaries. ## NOTES **addch**, **mvaddch**, **mvwaddch**, and **echochar** may be implemented as macros. ## EXTENSIONS The symbols (*ACS\_S3*, *ACS\_S7*, *ACS\_LEQUAL*, *ACS\_GEQUAL*, *ACS\_PI*, *ACS\_NEQUAL*, and *ACS\_STERLING*) were not documented in any publicly released System V and are not standard. However, many publicly available *terminfo* entries include *acs\_chars* (**acsc**) capabilities in which their key characters (**pryz{\|}**) are embedded, and a second-hand list of their character descriptions has come to light. The *ncurses* developers invented ACS-prefixed names for them. ## PORTABILITY Applications employing *ncurses* extensions should condition their use on the visibility of the **NCURSES\_VERSION** preprocessor macro. X/Open Curses Issue 4 describes these functions. It specifies no error conditions for them. SVr4 describes a successful return value only as “an integer value other than *ERR*”. The defaults specified for forms-drawing characters apply in the POSIX locale. ### ACS Symbols X/Open Curses states that the *ACS\_* definitions are *char* constants. Some implementations are problematic. - • Solaris *curses*, for example, defines the ACS symbols as constants; others define them as elements of an array. - SVr4 used an array, *acs\_map*, as does *ncurses*. NetBSD *curses* also uses an array, actually named *\_acs\_char*, with a “#define” for compatibility. - • HP-UX *curses* equates some of the *ACS\_* symbols to the analogous *WACS\_* symbols as if the *ACS\_* symbols were wide characters (see **add\_wch**(3NCURSES)). The misdefined symbols are the arrows and others that are not used for line drawing. - • X/Open Curses (Issues 2 through 7) has a typographical error for the *ACS\_LANTERN* symbol, equating its “VT100+ Character” to “I” (capital I), while the header files for SVr4 *curses* and other implementations use “i” (small i). - None of the terminal descriptions on Unix platforms use uppercase I, except for Solaris (in its *terminfo* entry for [*screen*(1)](/screen/1.md), apparently based on the X/Open documentation around 1995). On the other hand, its **gs6300** (AT&T PC6300 with EMOTS Terminal Emulator) description uses lowercase i. The *displayed* values of *ACS\_* constants depend on - • the *ncurses* ABI—for example, wide-character versus non-wide-character configurations (the former is capable of displaying Unicode while the latter is not), and - • whether the locale uses UTF-8 encoding. In certain cases, the terminal is unable to display forms-drawing characters *except* by using UTF-8; see the discussion of the *NCURSES\_NO\_UTF8\_ACS* environment variable in **ncurses**(3NCURSES). ### Character Set X/Open Curses assumes that the parameter passed to *waddch* contains a single character. That character may have been more than eight bits wide in an SVr3 or SVr4 implementation, but X/Open Curses leaves the width of a non-wide character code unspecified. The standard further does not specify the internal structure of a *chtype*, though the use of bit operations to combine the character code with attributes and a color pair identifier into a *chtype* for passage to *waddch* is common. A portable application uses only the macros discussed in **attr**(3NCURSES) to manipulate a *chtype*. In *ncurses*, *chtype* holds an eight-bit character, but the library allows a multibyte character sequence to be passed via a succession of calls to *waddch*. Other implementations do not; a *waddch* call transmits exactly one character, which may be rendered in one or more screen locations depending on whether it is printable (see **unctrl**(3NCURSES)). Depending on the locale, *ncurses* inspects the byte passed in each *waddch* call and checks whether the latest call continues a multibyte character. When a character is *complete*, *ncurses* displays the character and advances the cursor. If the calling application interrupts the succession of bytes in a multibyte character sequence by changing the current location—for example, with **wmove**(3NCURSES)—*ncurses* discards the incomplete character. For portability to other implementations, do not rely upon the foregoing behavior. Check whether a character can be represented as a single byte in the current locale. - • If it can, call either *waddch* or *wadd\_wch*. - • If it cannot, use only *wadd\_wch*. ## HISTORY 4BSD (1980) introduced *waddch* and its variants. SVr3 (1987) added the *echochar* and *wechochar* functions and most of the *ACS\_* constants, except for *ACS\_GEQUAL*, *ACS\_LEQUAL*, *ACS\_NEQUAL*, *ACS\_PI*, *ACS\_S3*, *ACS\_S7*, and *ACS\_STERLING*. *ncurses* 1.9.6 (1995) furnished the remaining *ACS\_* constants. ## SEE ALSO **add\_wch**(3NCURSES) describes comparable functions of the *ncurses* library in its wide-character configuration (*ncursesw*). **ncurses**(3NCURSES), **addchstr**(3NCURSES), **addstr**(3NCURSES), **attr**(3NCURSES), **bkgd**(3NCURSES), **clear**(3NCURSES), **inch**(3NCURSES), **outopts**(3NCURSES), **refresh**(3NCURSES), **curses\_variables**(3NCURSES), [**putchar**(3)](/putchar/3.md)