ncurses/man/curs_util.3x

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.\" $Id: curs_util.3x,v 1.151 2025/11/12 01:06:36 tom Exp $
.TH curs_util 3X 2025-11-11 "ncurses @NCURSES_MAJOR@.@NCURSES_MINOR@" "Library calls"
.ie \n(.g \{\
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.SH NAME
\fB\%delay_output\fP,
\fB\%filter\fP,
\fB\%flushinp\fP,
\fB\%getwin\fP,
\fB\%key_name\fP,
\fB\%keyname\fP,
\fB\%nofilter\fP,
\fB\%putwin\fP,
\fB\%unctrl\fP,
\fB\%use_env\fP,
\fB\%use_tioctl\fP,
\fB\%wunctrl\fP \-
miscellaneous \fIcurses\fR utility routines
.SH SYNOPSIS
.nf
\fB#include <curses.h>
.PP
\fBconst char * unctrl(chtype \fIch\fP);
\fBwchar_t * wunctrl(cchar_t * \fIwch\fP);
.PP
\fBconst char * keyname(int \fIc\fP);
\fBconst char * key_name(wchar_t \fIwc\fP);
.PP
\fBvoid filter(void);
\fI/* extension */
\fBvoid nofilter(void);
.PP
\fBvoid use_env(bool \fIbf\fP);
\fI/* extension */
\fBvoid use_tioctl(bool \fIbf\fP);
.PP
\fBint putwin(WINDOW * \fIwin\fP, FILE * \fIfilep\fP);
\fBWINDOW * getwin(FILE * \fIfilep\fP);
.PP
\fBint delay_output(int \fIms\fP);
.PP
\fBint flushinp(void);
.fi
.SH DESCRIPTION
.SS "unctrl, wunctrl"
.B unctrl
returns a null-terminated character string printably representing the
.I curses
character
.IR ch ,
often one that originated in keyboard input;
see \fBgetch\fP(3X).
.bP
Printable characters represent themselves as a one-character string.
.bP
Control characters are expressed in
.BI \*^ X
notation,
where
.I X
is the printable symbol of the control code's value plus 32
in the ISO\ 646/\*(``ASCII\*('' character set.
.bP
DEL
(character code 127)
is represented as
.BR \*^? .
.bP
A character code greater than 127 is represented in one of two ways.
.IP
If the screen has not been initialized or is in meta mode
(see \fBmeta\fP(3X)),
it is expressed in
.BI M- X
notation,
where X
is the representation of the code's value minus 128,
as described above.
.IP
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.
.IP
.IR \%ncurses 's
\fB\%use_legacy_coding\fP(3X)
function configures
.BR \%unctrl 's
handling of these character codes.
.PP
.B \%wunctrl
returns a null-terminated wide-character string printably representing
the
.I curses
complex character
.IR wch .
.PP
Both functions ignore the attributes and color pair selection
of their argument.
.SS "keyname, key_name"
The \fBkeyname\fP routine returns a character string
corresponding to the key \fIc\fP.
Key codes are different from character codes.
.bP
Key codes below 256 are characters.
They are displayed using \fBunctrl\fP.
.bP
Values above 256 may be the codes for function keys.
The function key name is displayed.
.bP
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.
.LP
The corresponding \fBkey_name\fP returns
a multibyte character string corresponding
to the wide-character value \fIwc\fP.
The two functions
(\fBkeyname\fP and \fBkey_name\fP)
do not return the same set of strings:
.bP
\fBkeyname\fP returns null where \fBkey_name\fP
would display a meta character.
.bP
\fBkey_name\fP does not return the name of a function key.
.SS "filter, nofilter"
The \fBfilter\fP routine,
if used,
must be called before \fBinitscr\fP or
\fBnewterm\fP are called.
Calling \fBfilter\fP causes these changes in initialization:
.bP
\fBLINES\fP is set to 1;
.bP
the capabilities
\fBclear\fP,
\fBcud1\fP,
\fBcud\fP,
\fBcup\fP,
\fBcuu1\fP,
\fBcuu\fP,
\fBvpa\fP
are disabled;
.bP
the capability \fBed\fP is disabled if \fBbce\fP is set;
.bP
and the \fBhome\fP string is set to the value of \fBcr\fP.
.PP
The \fBnofilter\fP routine cancels the effect
of a preceding \fBfilter\fP call.
That allows the caller to initialize a screen on a different device,
using a different value of \fB$TERM\fP.
The limitation arises because the \fBfilter\fP routine modifies the
in-memory copy of the terminal information.
.SS use_env
The \fBuse_env\fP routine,
if used,
should be called before \fBinitscr\fP or
\fBnewterm\fP are called
(because those compute the screen size).
It modifies the way \fI\%ncurses\fP treats environment variables
when determining the screen size.
.bP
Normally \fI\%ncurses\fP looks first at the terminal database for the
screen size.
.IP
If \fBuse_env\fP was called with \fBFALSE\fP for parameter,
it stops here unless
\fBuse_tioctl\fP was also called with \fBTRUE\fP for parameter.
.bP
Then it asks for the screen size via operating system calls.
If successful,
it overrides the values from the terminal database.
.bP
Finally
(unless \fBuse_env\fP was called with \fBFALSE\fP parameter),
\fI\%ncurses\fP examines the \fILINES\fP or \fI\%COLUMNS\fP environment
variables,
using a value in those to override the results
from the operating system or terminal database.
.IP
.I curses
also updates the screen size in response to
.IR \%SIGWINCH ","
unless overridden by the \fILINES\fP or \fI\%COLUMNS\fP environment
variables,
.SS use_tioctl
The \fBuse_tioctl\fP routine,
if used,
should be called before \fBinitscr\fP or \fBnewterm\fP are called
(because those compute the screen size).
After \fBuse_tioctl\fP is called with \fBTRUE\fP as an argument,
\fI\%ncurses\fP modifies the last step in its computation
of screen size as follows:
.bP
checks whether the \fILINES\fP and \fI\%COLUMNS\fP environment variables
are set to a number greater than zero.
.bP
for each,
\fI\%ncurses\fP updates the corresponding environment variable
with the value that it has obtained via operating system call
or from the terminal database.
.bP
\fI\%ncurses\fP re-fetches the value of the environment variables so
that it is still the environment variables that set the screen size.
.PP
The \fB\%use_env\fP and \fB\%use_tioctl\fP routines combine as follows.
.IP
.TS
Lb Lb Lb
Lb Lb Lw(29n)x.
use_env	use_tioctl	Summary
_
TRUE	FALSE	T{
\fI\%ncurses\fP uses operating system calls
unless overridden by \fILINES\fP or \fI\%COLUMNS\fP environment
variables;
default.
T}
TRUE	TRUE	T{
\fI\%ncurses\fP updates \fILINES\fP and \fI\%COLUMNS\fP based on
operating system calls.
T}
FALSE	TRUE	T{
\fI\%ncurses\fP ignores \fILINES\fP and \fI\%COLUMNS\fP,
using operating system calls to obtain size.
T}
.TE
.SS "putwin, getwin"
The \fBputwin\fP routine writes all data associated
with window
(or pad)
\fIwin\fP into
the file to which \fIfilep\fP points.
This information can be later retrieved
using the \fBgetwin\fP function.
.PP
The \fBgetwin\fP routine reads window related data stored in the file by
\fBputwin\fP.
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:
.bP
the data written is a copy of the \fI\%WINDOW\fP structure,
and its associated character cells.
The format differs between the wide-character \%(\fIncursesw\fP) and
non-wide \%(\fIncurses\fP) libraries.
You can transfer data between the two,
however.
.bP
the retrieved window is always created as a top-level window
(or pad),
rather than a subwindow.
.bP
the window's character cells contain the color pair \fIvalue\fP,
but not the actual color \fInumbers\fP.
If cells in the retrieved window use color pairs that have not been
created in the application using \fBinit_pair\fP,
they will not be colored when the window is refreshed.
.SS delay_output
The \fBdelay_output\fP routine inserts an \fIms\fP millisecond pause
in output.
Employ this function judiciously when terminal output uses padding,
because \fI\%ncurses\fP transmits null characters
(consuming CPU and I/O resources)
instead of sleeping and requesting resumption from the operating system.
Padding is used unless:
.bP
the terminal description has \fBnpc\fP (\fBno_pad_char\fP) capability,
or
.bP
the environment variable \fB\%NCURSES_NO_PADDING\fP is set.
.PP
If padding is not in use,
\fI\%ncurses\fP uses \fBnapms\fP to perform the delay.
If the value of \fIms\fP exceeds 30,000
(thirty seconds),
it is capped at that value.
.SS flushinp
The \fBflushinp\fP routine throws away any typeahead
that has been typed by the user
and has not yet been read by the program.
.SH RETURN VALUE
Except for
.BR \%flushinp ","
functions that return integers return
.B ERR
upon failure and
.B OK
upon success.
.PP
Functions that return pointers return a null pointer on failure.
.PP
In
.IR \%ncurses ","
.bP
.B \%flushinp
returns
.B ERR
if the terminal was not initialized,
and
.bP
.B \%putwin
returns
.B ERR
if its associated \fIwrite\fP(2) calls return
.BR ERR "."
.SH NOTES
.B \%wunctrl
is part of
.IR \%ncurses "'s"
wide-character API,
and is not available in its non-wide-character configuration.
.SH PORTABILITY
X/Open Curses Issue\ 4 describes these functions.
It specifies no error conditions for them.
.PP
SVr4 describes a successful return value only as
\*(``an integer value other than
.IR ERR \*(''. \" Courier roman in source; SVID 4, vol. 3, p. 542
.SS filter
The SVr4 documentation describes the action of \fBfilter\fP
only in the vaguest terms.
The description here is adapted from X/Open Curses
(which erroneously fails to describe the disabling of \fBcuu\fP).
.SS "delay_output padding"
The limitation to 30 seconds
and the use of \fBnapms\fP
differ from other implementations.
.bP
SVr4
.I curses
does not delay if no padding character is available.
.bP
NetBSD
.I curses
uses \fBnapms\fP when no padding character is available,
but does not take timing into account when using the padding character.
.PP
Neither limits the delay.
.SS keyname
The \fBkeyname\fP function may return the names of user-defined
string capabilities that are defined in the terminfo entry
via the \fB\-x\fP
option of \fB@TIC@\fP.
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 \fBuse_extended_names\fP(3X) function controls whether this data is
loaded when the terminal description is read by the library.
.SS "nofilter, use_tioctl"
The \fBnofilter\fP and \fBuse_tioctl\fP routines are specific to
\fI\%ncurses\fP.
They were not supported on Version 7,
BSD or System V implementations.
It is recommended that any code depending on \fI\%ncurses\fP extensions
be conditioned using \fBNCURSES_VERSION\fP.
.SS "putwin/getwin file-format"
The \fBputwin\fP and \fBgetwin\fP functions have several issues with
portability:
.bP
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.
.IP
Interestingly enough,
according to the copyright dates in Solaris source,
the functions
(along with \fBscr_init\fP,
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
.I curses
sources.
.bP
Most implementations simply dump the binary
.I \%WINDOW
structure
to the file.
These include SVr4
.IR curses ,
NetBSD
.IR curses ,
and
.IR \%PDCurses ,
as well as older \fI\%ncurses\fP versions.
This implementation
(as well as
.IR \%xcurses ","
the X/Open variant of Solaris
.IR curses ","
dated 1995)
uses textual dumps.
.IP
The implementations that use binary dumps use block I/O
(\fIwrite\fP(2) and \fIread\fP(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.
.SS "unctrl, wunctrl"
X/Open Curses Issue\ 4 describes these functions.
It specifies no error conditions for them.
It states that \fBunctrl\fP and \fBwunctrl\fP will return a null pointer
if unsuccessful.
This implementation checks for three cases:
.bP
the parameter is a 7-bit US\-ASCII code.
This is the case that X/Open Curses documented.
.bP
the parameter is in the range 128\-159,
i.e.,
a C1 control code.
If \fB\%use_legacy_coding\fP(3X) has been called with a \fB2\fP parameter,
\fBunctrl\fP 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.
.IP
X/Open Curses does not document whether \fBunctrl\fP can be called
before initializing
.IR curses "."
This implementation permits that,
and returns the \*(``\*~@\*('',
etc.,
values in that case.
.bP
parameter values outside the 0 to 255 range.
\fBunctrl\fP returns a null pointer.
.PP
The strings returned by \fBunctrl\fP 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 \fB\%use_legacy_coding\fP(3X) function allows the caller to
change the output of \fBunctrl\fP.
.PP
Likewise,
the \fBmeta\fP(3X) function allows the caller to change the output
of \fBkeyname\fP,
i.e.,
it determines whether to use the \*(``M\-\*('' prefix
for \*(``meta\*('' keys (codes in the range 128 to 255).
Both \fB\%use_legacy_coding\fP(3X) and \fBmeta\fP(3X) succeed only after
.I curses
is initialized.
X/Open Curses does not document the treatment of codes 128 to 159.
When treating them as \*(``meta\*('' keys
(or if \fBkeyname\fP is called before initializing
.IR curses "),"
this implementation returns strings \*(``M\-\*^@\*('',
\*(``M\-\*^A\*('',
etc.
.PP
X/Open Curses documents
.I \%unctrl
as declared in
.IR \%unctrl.h ","
which
.I \%ncurses
does.
However,
.IR \%ncurses 's
.I \%curses.h
includes
.IR \%unctrl.h ","
matching the behavior of SVr4
.IR curses "."
Other implementations may not do that.
.SS "use_env, use_tioctl"
If \fI\%ncurses\fP is configured to provide the sp-functions extension,
the state of \fBuse_env\fP and \fBuse_tioctl\fP may be updated before
creating each \fIscreen\fP rather than once only
(\fBcurs_sp_funcs\fP(3X)).
This feature of \fBuse_env\fP
is not provided by other implementations of
.IR curses "."
.SH HISTORY
4BSD (1980)
introduced
.IR \%unctrl ","
defining it as a macro
in
.IR \%unctrl.h "."
.PP
SVr2 (1984)
added
.IR \%delay_output ","
.IR \%flushinp ","
and
.IR \%keyname "."
.PP
SVr3 (1987) supplied
.IR \%filter "."
Later that year,
SVr3.1 brought
.I \%getwin
and
.IR \%putwin ","
reading and writing window dumps
with \fI\%fread\fP(3) and \fI\%fwrite\fP(3),
respectively.
.PP
SVr4 (1989) furnished
.IR \%use_env "."
.PP
X/Open Curses Issue\ 4 (1995) specified
.I \%key_name
and
.IR \%wunctrl "."
.PP
.I \%ncurses
5.6 (2006) added
.IR \%nofilter "," \" 20060107
and 6.0 (2015)
.IR \%use_tioctl "." \" 20120714
.SH SEE ALSO
.na
\fB\%curses\fP(3X),
\fB\%curs_initscr\fP(3X),
\fB\%curs_inopts\fP(3X),
\fB\%curs_kernel\fP(3X),
\fB\%curs_scr_dump\fP(3X),
\fB\%curs_sp_funcs\fP(3X),
\fB\%curs_variables\fP(3X),
\fB\%legacy_coding\fP(3X)
.ad