curs_addch(3x) — Linux manual page


curs_addch(3X)                                            curs_addch(3X)

NAME         top

       addch, waddch, mvaddch, mvwaddch, echochar, wechochar - add a
       character (with attributes) to a curses window, then advance the

SYNOPSIS         top

       #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);

DESCRIPTION         top

   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

       •   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

RETURN VALUE         top

       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

       •   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.

NOTES         top

       Note that addch, mvaddch, mvwaddch, and echochar may be macros.

PORTABILITY         top

       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

           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

       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

       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

       •   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

       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.

SEE ALSO         top

       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).

COLOPHON         top

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