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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | PORTABILITY | HISTORY | SEE ALSO | COLOPHON |
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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, wunctrl
unctrl returns a null-terminated character string printably
representing the curses character ch, often one that originated in
keyboard input; see getch(3X).
• Printable characters represent themselves as a one-character
string.
• 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.
• DEL (character code 127) is represented as ^?.
• 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.
keyname, key_name
The keyname routine returns a character string corresponding to
the key c. Key codes are different from character codes.
• Key codes below 256 are characters. They are displayed using
unctrl.
• Values above 256 may be the codes for function keys. The
function key name is displayed.
• 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:
• keyname returns null where key_name would display a meta
character.
• key_name does not return the name of a function key.
filter, nofilter
The filter routine, if used, must be called before initscr or
newterm are called. Calling filter causes these changes in
initialization:
• 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
different 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
determining 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
operating system or terminal database.
curses also updates the screen size in response to SIGWINCH,
unless overridden by the LINES or COLUMNS environment
variables,
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
modifies the last step in its computation of screen size as
follows:
• checks whether the LINES and COLUMNS environment variables are
set to a number greater than zero.
• for each, ncurses updates the corresponding environment
variable 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 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.
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 that have not been created in the
application 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
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:
• the terminal description has npc (no_pad_char) capability, or
• 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.
flushinp
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,
• flushinp returns ERR if the terminal was not initialized, and
• 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”.
filter
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).
delay_output padding
The limitation to 30 seconds and the use of napms differ from
other implementations.
• SVr4 curses does not delay if no padding character is
available.
• 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.
keyname
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.
nofilter, use_tioctl
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.
putwin/getwin file-format
The putwin and getwin functions have several issues with
portability:
• 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.
• 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.
unctrl, wunctrl
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:
• 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
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.
• 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.
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 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)
This page is part of the ncurses (new curses) project.
Information about the project can be found at
⟨https://invisible-island.net/ncurses/ncurses.html⟩. If you have a
bug report for this manual page, send it to bug-ncurses@gnu.org.
This page was obtained from the tarball ncurses-6.6.tar.gz fetched
from ⟨https://ftp.gnu.org/gnu/ncurses/⟩ on 2026-01-16. 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 man-pages@man7.org
ncurses @NCURSES_MAJOR@.@NCU... 2025-11-11 curs_util(3X)
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HTML rendering created 2026-01-16 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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