https://invisible-island.net/ncurses/man/
curs_util(3x) Library calls curs_util(3x)
delay_output, filter, flushinp, getwin, key_name, keyname, nofilter,
putwin, unctrl, use_env, use_tioctl, wunctrl - miscellaneous curses
utility routines
#include <curses.h>
const char * unctrl(chtype ch);
wchar_t * wunctrl(cchar_t * wch);
const char * keyname(int c);
const char * key_name(wchar_t wc);
void filter(void);
/* extension */
void nofilter(void);
void use_env(bool bf);
/* extension */
void use_tioctl(bool bf);
int putwin(WINDOW * win, FILE * filep);
WINDOW * getwin(FILE * filep);
int delay_output(int ms);
int flushinp(void);
unctrl returns a null-terminated character string printably
representing the curses character ch, often one that originated in
keyboard input; see getch(3x).
o Printable characters represent themselves as a one-character
string.
o Control characters are expressed in ^X notation, where X is the
printable symbol of the control code's value plus 32 in the
ISO 646/"ASCII" character set.
o DEL (character code 127) is represented as ^?.
o A character code greater than 127 is represented in one of two
ways.
If the screen has not been initialized or is in meta mode (see
meta(3x)), it is expressed in M-X notation, where X is the
representation of the code's value minus 128, as described above.
If the screen is not in meta mode, the character code is assumed to
represent itself. It nevertheless may not be printable; this is
the case for character codes 128-159 in ISO 8859 encodings.
ncurses's use_legacy_coding(3x) function configures unctrl's
handling of these character codes.
wunctrl returns a null-terminated wide-character string printably
representing the curses complex character wch.
Both functions ignore the attributes and color pair selection of their
argument.
The keyname routine returns a character string corresponding to the key
c. Key codes are different from character codes.
o Key codes below 256 are characters. They are displayed using
unctrl.
o Values above 256 may be the codes for function keys. The function
key name is displayed.
o Otherwise (if there is no corresponding name and the key is not a
character) the function returns null, to denote an error. X/Open
also lists an "UNKNOWN KEY" return value, which some
implementations return rather than null.
The corresponding key_name returns a multibyte character string
corresponding to the wide-character value wc. The two functions
(keyname and key_name) do not return the same set of strings:
o keyname returns null where key_name would display a meta character.
o key_name does not return the name of a function key.
The filter routine, if used, must be called before initscr or newterm
are called. Calling filter causes these changes in initialization:
o LINES is set to 1;
o the capabilities clear, cud1, cud, cup, cuu1, cuu, vpa are
disabled;
o the capability ed is disabled if bce is set;
o 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 different device,
using a different value of $TERM. The limitation arises because the
filter routine modifies the in-memory copy of the terminal information.
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 determining
the screen size.
o 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.
o Then it asks for the screen size via operating system calls. If
successful, it overrides the values from the terminal database.
o 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 operating system or
terminal database.
curses also updates the screen size in response to SIGWINCH, unless
overridden by the LINES or COLUMNS environment variables,
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 modifies the
last step in its computation of screen size as follows:
o checks whether the LINES and COLUMNS environment variables are set
to a number greater than zero.
o for each, ncurses updates the corresponding environment variable
with the value that it has obtained via operating system call or
from the terminal database.
o ncurses re-fetches the value of the environment variables so that
it is still the environment variables that set the screen size.
The use_env and use_tioctl routines combine as follows.
use_env use_tioctl Summary
-----------------------------------------------------------------
TRUE FALSE ncurses uses operating system calls
unless overridden by LINES or COLUMNS
environment variables; default.
TRUE TRUE ncurses updates LINES and COLUMNS based
on operating system calls.
FALSE TRUE ncurses ignores LINES and COLUMNS, using
operating system calls to obtain size.
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:
o 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.
o the retrieved window is always created as a top-level window (or
pad), rather than a subwindow.
o 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 that have not been created in the application using
init_pair, they will not be colored when the window is refreshed.
The delay_output routine inserts an ms millisecond pause in output.
Employ this function judiciously when terminal output uses padding,
because ncurses transmits null characters (consuming CPU and I/O
resources) instead of sleeping and requesting resumption from the
operating system. Padding is used unless:
o the terminal description has npc (no_pad_char) capability, or
o the environment variable NCURSES_NO_PADDING is set.
If padding is not in use, ncurses uses napms to perform the delay. If
the value of ms exceeds 30,000 (thirty seconds), it is capped at that
value.
The flushinp routine throws away any typeahead that has been typed by
the user and has not yet been read by the program.
Except for flushinp, functions that return integers return ERR upon
failure and OK upon success.
Functions that return pointers return a null pointer on failure.
In ncurses,
o flushinp returns ERR if the terminal was not initialized, and
o putwin returns ERR if its associated write(2) calls return ERR.
wunctrl is part of ncurses's wide-character API, and is not available
in its non-wide-character configuration.
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 SVr4 documentation describes the action of filter only in the
vaguest terms. The description here is adapted from X/Open Curses
(which erroneously fails to describe the disabling of cuu).
The limitation to 30 seconds and the use of napms differ from other
implementations.
o SVr4 curses does not delay if no padding character is available.
o NetBSD curses uses napms when no padding character is available,
but does not take timing into account when using the padding
character.
Neither limits the delay.
The keyname function may return the names of user-defined string
capabilities that are defined in the terminfo entry via the -x option
of tic. This implementation automatically assigns at run-time key
codes to user-defined strings that begin with "k". The key codes 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 that have been loaded. The use_extended_names(3x)
function controls whether this data is loaded when the terminal
description is read by the library.
The nofilter and use_tioctl routines are specific to ncurses. They
were not supported on Version 7, BSD or System V implementations. It
is recommended that any code depending on ncurses extensions be
conditioned using NCURSES_VERSION.
The putwin and getwin functions have several issues with portability:
o The files written and read by these functions use an
implementation-specific format. Although the format is an obvious
target for standardization, it has been overlooked.
Interestingly enough, according to the copyright dates in Solaris
source, the functions (along with scr_init, etc.) originated 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.
o Most implementations simply dump the binary WINDOW structure to the
file. These include SVr4 curses, NetBSD curses, and PDCurses, as
well as older ncurses versions. This implementation (as well as
xcurses, the X/Open variant of Solaris curses, dated 1995) uses
textual dumps.
The implementations that use binary dumps use block I/O (write(2)
and read(2) functions). Those that use textual dumps use buffered
I/O. A few applications may happen to write extra data in the file
using these functions. Doing that can run into problems mixing
block and buffered I/O. This implementation reduces the problem on
writes by flushing the output. However, reading from a file
written using mixed schemes may not be successful.
X/Open Curses Issue 4 describes these functions. It specifies no error
conditions for them. It states that unctrl and wunctrl will return a
null pointer if unsuccessful. This implementation checks for three
cases:
o the parameter is a 7-bit US-ASCII code. This is the case that
X/Open Curses documented.
o 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 parameter, 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 controls.
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.
o parameter values outside the 0 to 255 range. unctrl returns a null
pointer.
The strings returned by unctrl in this implementation are determined 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 upper-128 codes as printable.
This implementation uses 8 bits but does not modify the string to
reflect locale. The use_legacy_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 keyname 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's curses.h includes unctrl.h, matching the
behavior of SVr4 curses. Other implementations may not do that.
If ncurses is configured to provide the sp-functions extension, the
state of use_env and use_tioctl may be updated before creating each
screen rather than once only (curs_sp_funcs(3x)). This feature of
use_env is not provided by other implementations of curses.
4BSD (1980) introduced unctrl, defining it as a macro in unctrl.h.
SVr2 (1984) added delay_output, flushinp, and keyname.
SVr3 (1987) supplied filter. Later that year, SVr3.1 brought getwin
and putwin, reading and writing window dumps with fread(3) and
fwrite(3), respectively.
SVr4 (1989) furnished use_env.
X/Open Curses Issue 4 (1995) specified key_name and wunctrl.
ncurses 5.6 (2006) added nofilter, and 6.0 (2015) use_tioctl.
curses(3x), curs_initscr(3x), curs_inopts(3x), curs_kernel(3x),
curs_scr_dump(3x), curs_sp_funcs(3x), curs_variables(3x),
legacy_coding(3x)
ncurses 6.5 2025-10-04 curs_util(3x)