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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | PORTABILITY | SEE ALSO | COLOPHON |
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curs_addch(3X) curs_addch(3X)
addch, waddch, mvaddch, mvwaddch, echochar, wechochar - add a
character (with attributes) to a curses window, then advance the
cursor
#include <curses.h>
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);
Adding characters
The addch, waddch, mvaddch and mvwaddch routines put the
character ch into the given window at its current window
position, which is then advanced. They are analogous to
putchar(3) in stdio(3). If the advance is at the right margin:
• The cursor automatically wraps to the beginning of the next
line.
• At the bottom of the current scrolling region, and if
scrollok(3X) is enabled, the scrolling region is scrolled up
one line.
• 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 ch is a tab, newline, carriage return or backspace, the cursor
is moved appropriately within the window:
• Backspace moves the cursor one character left; at the left
edge of a window it does nothing.
• Carriage return moves the cursor to the window left margin on
the current line.
• Newline does a clrtoeol, then moves the cursor to the window
left margin on the next line, scrolling the window if on the
last line.
• Tabs are considered to be at every eighth column. The tab
interval may be altered by setting the TABSIZE variable.
If ch is any other nonprintable character, it is drawn in
printable form, using the same convention as unctrl(3X):
• Control characters are displayed in the ^X notation.
• Values above 128 are either meta characters (if the screen
has not been initialized, or if meta(3X) has been called with
a TRUE E parameter), shown in the M-X notation, or are
displayed as themselves. In the latter case, the values may
not be printable; this follows the X/Open specification.
Calling winch after adding a nonprintable character does not
return the character itself, but instead returns the printable
representation of the character.
Video attributes can be combined with a character argument passed
to addch or related functions by logical-ORing them into the
character. (Thus, text, including attributes, can be copied from
one place to another using inch(3X) and addch.) See the
curs_attr(3X) page for values of predefined video attribute
constants that can be usefully OR'ed into characters.
Echoing characters
The echochar and wechochar routines are equivalent to a call to
addch followed by a call to refresh(3X), or a call to waddch
followed by a call to wrefresh. The knowledge that only a single
character is being output is used and, for non-control
characters, a considerable performance gain may be seen by using
these routines instead of their equivalents.
Line Graphics
The following variables may be used to add line drawing
characters to the screen with routines of the addch family. The
default character listed below is used if the acsc capability
does not define a terminal-specific replacement for it, or if the
terminal and locale configuration requires Unicode but the
library is unable to use Unicode.
The names are taken from VT100 nomenclature.
ACS ACS acsc Glyph
Name Default char 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
All routines return the integer ERR upon failure and OK on
success (the SVr4 manuals specify only “an integer value other
than ERR”) upon successful completion, unless otherwise noted in
the preceding routine descriptions.
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.
If it is not possible to add a complete character, an error is
returned:
• 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.
Note that addch, mvaddch, mvwaddch, and echochar may be macros.
All these functions are described in the XSI Curses standard,
Issue 4. 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. For the wide-character implementation (see
curs_add_wch), there are analogous WACS_ definitions which are
cchar_t constants. Some implementations are problematic:
• Some implementations define the ACS symbols to a constant
(such as Solaris), while others define those to entries in an
array.
This implementation uses an array acs_map, as done in SVr4
curses. NetBSD also uses an array, actually named _acs_char,
with a #define for compatibility.
• HPUX 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 (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
the various implementations use i (lowercase).
None of the terminal descriptions on Unix platforms use
uppercase-I, except for Solaris (i.e., screen's terminal
description, apparently based on the X/Open documentation
around 1995). On the other hand, the terminal description
gs6300 (AT&T PC6300 with EMOTS Terminal Emulator) uses
lowercase-i.
Some ACS symbols (ACS_S3, ACS_S7, ACS_LEQUAL, ACS_GEQUAL, ACS_PI,
ACS_NEQUAL, ACS_STERLING) were not documented in any publicly
released System V. However, many publicly available terminfos
include acsc strings in which their key characters (pryz{|}) are
embedded, and a second-hand list of their character descriptions
has come to light. The ACS-prefixed names for them were invented
for ncurses(3X).
The displayed values for the ACS_ and WACS_ constants depend on
• the library configuration, i.e., ncurses versus ncursesw,
where the latter is capable of displaying Unicode while the
former is not, and
• whether the locale uses UTF-8 encoding.
In certain cases, the terminal is unable to display line-drawing
characters except by using UTF-8 (see the discussion of
NCURSES_NO_UTF8_ACS in ncurses(3X)).
Character Set
X/Open Curses assumes that the parameter passed to waddch
contains a single character. As discussed in curs_attr(3X), that
character may have been more than eight bits in an SVr3 or SVr4
implementation, but in the X/Open Curses model, the details are
not given. The important distinction between SVr4 curses and
X/Open Curses is that the non-character information (attributes
and color) was separated from the character information which is
packed in a chtype to pass to waddch.
In this implementation, chtype holds an eight-bit character. But
ncurses allows multibyte characters to be passed in a succession
of calls to waddch. The other implementations do not do this; a
call to waddch passes exactly one character which may be rendered
as one or more cells on the screen depending on whether it is
printable.
Depending on the locale settings, ncurses will inspect the byte
passed in each call to waddch, and check if the latest call will
continue a multibyte sequence. When a character is complete,
ncurses displays the character and moves to the next position in
the screen.
If the calling application interrupts the succession of bytes in
a multibyte character by moving the current location (e.g., using
wmove), ncurses discards the partially built character, starting
over again.
For portability to other implementations, do not rely upon this
behavior:
• check if a character can be represented as a single byte in
the current locale before attempting call waddch, and
• call wadd_wch for characters which cannot be handled by
waddch.
TABSIZE
The TABSIZE variable is implemented in SVr4 and other versions of
curses, but is not part of X/Open curses (see curs_variables(3X)
for more details).
If ch is a carriage return, the cursor is moved to the beginning
of the current row of the window. This is true of other
implementations, but is not documented.
curses(3X), curs_attr(3X), curs_clear(3X), curs_inch(3X),
curs_outopts(3X), curs_refresh(3X), curs_variables(3X), putc(3).
Comparable functions in the wide-character (ncursesw) library are
described in curs_add_wch(3X).
This page is part of the ncurses (new curses) project.
Information about the project can be found at
⟨https://www.gnu.org/software/ncurses/ncurses.html⟩. If you have
a bug report for this manual page, send it to
[email protected]. This page was obtained from the
project's upstream Git mirror of the CVS repository
⟨https://github.com/mirror/ncurses.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2023-03-12.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
curs_addch(3X)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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