curs_util(3x) — Linux manual page

NAME \| SYNOPSIS \| DESCRIPTION \| RETURN VALUE \| PORTABILITY \| SEE ALSO \| COLOPHON

curs_util(3X)                                              curs_util(3X)

NAME top

       delay_output, filter, flushinp, getwin, key_name, keyname,
       nofilter, putwin, unctrl, use_env, use_tioctl, wunctrl -
       miscellaneous curses utility routines

SYNOPSIS top

       #include <curses.h>

       const char *unctrl(chtype c);
       wchar_t *wunctrl(cchar_t *c);

       const char *keyname(int c);
       const char *key_name(wchar_t w);

       void filter(void);
       void nofilter(void);

       void use_env(bool f);
       void use_tioctl(bool f);

       int putwin(WINDOW *win, FILE *filep);
       WINDOW *getwin(FILE *filep);

       int delay_output(int ms);
       int flushinp(void);

DESCRIPTION top

unctrl
The unctrl routine returns a character string which is a print‐
able representation of the character c, ignoring attributes.
Control characters are displayed in the ^X notation. Printing
characters are displayed as is.

The corresponding wunctrl returns a printable representation of a
wide character.

keyname/key_name
The keyname routine returns a character string corresponding to
the key c:

• Printable characters are displayed as themselves, e.g., a
one-character string containing the key.

• Control characters are displayed in the ^X notation.

• DEL (character 127) is displayed as ^?.

• Values above 128 are either meta characters (if the screen
has not been initialized, or if meta(3X) has been called with
a TRUE parameter), shown in the M-X notation, or are dis‐
played as themselves. In the latter case, the values may not
be printable; this follows the X/Open specification.

• Values above 256 may be the names of the names of function
keys.

• Otherwise (if there is no corresponding name) the function
returns null, to denote an error. X/Open also lists an “UN‐
KNOWN KEY” return value, which some implementations return
rather than null.

The corresponding key_name returns a character string correspond‐
ing to the wide-character value w. The two functions do not re‐
turn the same set of strings; the latter returns null where the
former would display a meta character.

filter/nofilter
The filter routine, if used, must be called before initscr or
newterm are called. Calling filter causes these changes in ini‐
tialization:

• LINES is set to 1;

• the capabilities clear, cud1, cud, cup, cuu1, cuu, vpa are
disabled;

• the capability ed is disabled if bce is set;

• and the home string is set to the value of cr.

The nofilter routine cancels the effect of a preceding filter
call. That allows the caller to initialize a screen on a differ‐
ent device, using a different value of $TERM. The limitation
arises because the filter routine modifies the in-memory copy of
the terminal information.

use_env
The use_env routine, if used, should be called before initscr or
newterm are called (because those compute the screen size). It
modifies the way ncurses treats environment variables when deter‐
mining the screen size.

• Normally ncurses looks first at the terminal database for the
screen size.

If use_env was called with FALSE for parameter, it stops here
unless use_tioctl was also called with TRUE for parameter.

• Then it asks for the screen size via operating system calls.
If successful, it overrides the values from the terminal
database.

• Finally (unless use_env was called with FALSE parameter),
ncurses examines the LINES or COLUMNS environment variables,
using a value in those to override the results from the oper‐
ating system or terminal database.

Ncurses also updates the screen size in response to SIGWINCH,
unless overridden by the LINES or COLUMNS environment vari‐
ables,

use_tioctl
The use_tioctl routine, if used, should be called before initscr
or newterm are called (because those compute the screen size).
After use_tioctl is called with TRUE as an argument, ncurses mod‐
ifies the last step in its computation of screen size as follows:

• checks if the LINES and COLUMNS environment variables are set
to a number greater than zero.

• for each, ncurses updates the corresponding environment vari‐
able with the value that it has obtained via operating system
call or from the terminal database.

• ncurses re-fetches the value of the environment variables so
that it is still the environment variables which set the
screen size.

The use_env and use_tioctl routines combine as summarized here:
use_env use_tioctl Summary
────────────────────────────────────────────────────────────────
TRUE FALSE This is the default behavior. ncurses
uses operating system calls unless over‐
ridden by $LINES or $COLUMNS environment
variables.
TRUE TRUE ncurses updates $LINES and $COLUMNS
based on operating system calls.
FALSE TRUE ncurses ignores $LINES and $COLUMNS, us‐
es operating system calls to obtain
size.
FALSE FALSE ncurses relies on the terminal database
to determine size.

putwin/getwin
The putwin routine writes all data associated with window (or
pad) win into the file to which filep points. This information
can be later retrieved using the getwin function.

The getwin routine reads window related data stored in the file
by putwin. The routine then creates and initializes a new window
using that data. It returns a pointer to the new window. There
are a few caveats:

• the data written is a copy of the WINDOW structure, and its
associated character cells. The format differs between the
wide-character (ncursesw) and non-wide (ncurses) libraries.
You can transfer data between the two, however.

• the retrieved window is always created as a top-level window
(or pad), rather than a subwindow.

• the window's character cells contain the color pair value,
but not the actual color numbers. If cells in the retrieved
window use color pairs which have not been created in the ap‐
plication using init_pair, they will not be colored when the
window is refreshed.

delay_output
The delay_output routine inserts an ms millisecond pause in out‐
put. This routine should not be used extensively because padding
characters are used rather than a CPU pause. If no padding char‐
acter is specified, this uses napms to perform the delay.

flushinp
The flushinp routine throws away any typeahead that has been
typed by the user and has not yet been read by the program.

RETURN VALUE top

       Except for flushinp, routines that return an integer return ERR
       upon failure and OK (SVr4 specifies only "an integer value other
       than ERR") upon successful completion.

       Routines that return pointers return NULL on error.

       X/Open does not define any error conditions.  In this implementa‐
       tion

          flushinp
               returns an error if the terminal was not initialized.

          putwin
               returns an error if the associated fwrite calls return an
               error.

PORTABILITY top

   filter
       The SVr4 documentation describes the action of filter only in the
       vaguest terms.  The description here is adapted from the XSI
       Curses standard (which erroneously fails to describe the dis‐
       abling of cuu).

   keyname
       The keyname function may return the names of user-defined string
       capabilities which are defined in the terminfo entry via the -x
       option of @TIC@.  This implementation automatically assigns at
       run-time keycodes to user-defined strings which begin with “k”.
       The keycodes start at KEY_MAX, but are not guaranteed to be the
       same value for different runs because user-defined codes are
       merged from all terminal descriptions which have been loaded.
       The use_extended_names(3X) function controls whether this data is
       loaded when the terminal description is read by the library.

   nofilter/use_tioctl
       The nofilter and use_tioctl routines are specific to ncurses.
       They were not supported on Version 7, BSD or System V implementa‐
       tions.  It is recommended that any code depending on ncurses ex‐
       tensions be conditioned using NCURSES_VERSION.

   putwin/getwin file-format
       The putwin and getwin functions have several issues with porta‐
       bility:

       •   The files written and read by these functions use an imple‐
           mentation-specific format.  Although the format is an obvious
           target for standardization, it has been overlooked.

           Interestingly enough, according to the copyright dates in So‐
           laris source, the functions (along with scr_init, etc.) orig‐
           inated with the University of California, Berkeley (in 1982)
           and were later (in 1988) incorporated into SVr4.  Oddly,
           there are no such functions in the 4.3BSD curses sources.

       •   Most implementations simply dump the binary WINDOW structure
           to the file.  These include SVr4 curses, NetBSD and PDCurses,
           as well as older ncurses versions.  This implementation (as
           well as the X/Open variant of Solaris curses, dated 1995) us‐
           es textual dumps.

           The implementations which use binary dumps use block-I/O (the
           fwrite and fread functions).  Those that use textual dumps
           use buffered-I/O.  A few applications may happen to write ex‐
           tra data in the file using these functions.  Doing that can
           run into problems mixing block- and buffered-I/O.  This im‐
           plementation reduces the problem on writes by flushing the
           output.  However, reading from a file written using mixed
           schemes may not be successful.

   unctrl/wunctrl
       The XSI Curses standard, Issue 4 describes these functions.  It
       states that unctrl and wunctrl will return a null pointer if un‐
       successful, but does not define any error conditions.  This im‐
       plementation checks for three cases:

       •   the parameter is a 7-bit US-ASCII code.  This is the case
           that X/Open Curses documented.

       •   the parameter is in the range 128-159, i.e., a C1 control
           code.  If use_legacy_coding(3X) has been called with a 2 pa‐
           rameter, unctrl returns the parameter, i.e., a one-character
           string with the parameter as the first character.  Otherwise,
           it returns “~@”, “~A”, etc., analogous to “^@”, “^A”, C0 con‐
           trols.

           X/Open Curses does not document whether unctrl can be called
           before initializing curses.  This implementation permits
           that, and returns the “~@”, etc., values in that case.

       •   parameter values outside the 0 to 255 range.  unctrl returns
           a null pointer.

       The strings returned by unctrl in this implementation are deter‐
       mined at compile time, showing C1 controls from the upper-128
       codes with a “~” prefix rather than “^”.  Other implementations
       have different conventions.  For example, they may show both sets
       of control characters with “^”, and strip the parameter to 7
       bits.  Or they may ignore C1 controls and treat all of the up‐
       per-128 codes as printable.  This implementation uses 8 bits but
       does not modify the string to reflect locale.  The use_lega‐
       cy_coding(3X) function allows the caller to change the output of
       unctrl.

       Likewise, the meta(3X) function allows the caller to change the
       output of keyname, i.e., it determines whether to use the “M-”
       prefix for “meta” keys (codes in the range 128 to 255).  Both
       use_legacy_coding(3X) and meta(3X) succeed only after curses is
       initialized.  X/Open Curses does not document the treatment of
       codes 128 to 159.  When treating them as “meta” keys (or if key‐
       name is called before initializing curses), this implementation
       returns strings “M-^@”, “M-^A”, etc.

       X/Open Curses documents unctrl as declared in <unctrl.h>, which
       ncurses does.  However, ncurses' <curses.h> includes <unctrl.h>,
       matching the behavior of SVr4 curses.  Other implementations may
       not do that.

   use_env/use_tioctl
       If ncurses is configured to provide the sp-functions extension,
       the state of use_env and use_tioctl may be updated before creat‐
       ing each screen rather than once only (curs_sp_funcs(3X)).  This
       feature of use_env is not provided by other implementation of
       curses.

COLOPHON top

       This page is part of the ncurses (new curses) project.  Informa‐
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       a bug report for this manual page, send it to
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       ⟨https://github.com/mirror/ncurses.git⟩ on 2024-06-14.  (At that
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                                                           curs_util(3X)