curs_util(3X) Library calls curs_util(3X)
NAME
delay_output, filter, flushinp, getwin, key_name, keyname, nofilter,
putwin, unctrl, use_env, use_tioctl, wunctrl - miscellaneous curses
utility routines
SYNOPSIS
#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);
DESCRIPTION
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).
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.
keyname, key_name
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.
filter, nofilter
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.
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.
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,
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:
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.
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:
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.
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:
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.
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
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.
NOTES
wunctrl is part of ncurses's wide-character API, and is not available in
its non-wide-character configuration.
PORTABILITY
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.
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.
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:
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.
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:
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.
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.
HISTORY
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.
SEE ALSO
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 6.6 2025-11-11 curs_util(3X)