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.\" $Id: curs_util.3,v 1.7 2023/10/17 09:52:08 nicm Exp $
.TH curs_util 3 2023-08-19 "ncurses 6.4" "Library calls"
.ie \n(.g .ds `` \(lq
.el       .ds `` ``
.ie \n(.g .ds '' \(rq
.el       .ds '' ''
.de bP
.ie n  .IP \(bu 4
.el    .IP \(bu 2
..
.na
.hy 0
.SH NAME
\fBdelay_output\fP,
\fBfilter\fP,
\fBflushinp\fP,
\fBgetwin\fP,
\fBkey_name\fP,
\fBkeyname\fP,
\fBnofilter\fP,
\fBputwin\fP,
\fBunctrl\fP,
\fBuse_env\fP,
\fBuse_tioctl\fP,
\fBwunctrl\fP \- miscellaneous \fBcurses\fP utility routines
.ad
.hy
.SH SYNOPSIS
\fB#include <curses.h>\fP
.sp
\fBconst char *unctrl(chtype \fIc\fB);\fR
.br
\fBwchar_t *wunctrl(cchar_t *\fIc\fB);\fR
.sp
\fBconst char *keyname(int \fIc\fB);\fR
.br
\fBconst char *key_name(wchar_t \fIw\fB);\fR
.sp
\fBvoid filter(void);\fP
.sp
\fBvoid use_env(bool \fIf\fB);\fR
.sp
\fBint putwin(WINDOW *\fIwin\fB, FILE *\fIfilep\fB);\fR
.br
\fBWINDOW *getwin(FILE *\fIfilep\fB);\fR
.sp
\fBint delay_output(int \fIms\fB);\fR
.br
\fBint flushinp(void);\fP
.sp
/* extensions */
.br
\fBvoid nofilter(void);\fP
.br
\fBvoid use_tioctl(bool \fIf\fB);\fR
.SH DESCRIPTION
.SS unctrl
The \fBunctrl\fP routine returns a character string which is a printable
representation of the character \fIc\fP:
.bP
Printable characters are displayed as themselves,
e.g., a one-character string containing the key.
.bP
Control characters are displayed in the \fB^\fIX\fR notation.
.bP
Printing characters are displayed as is.
.bP
DEL (character 127) is displayed as \fB^?\fP.
.bP
Values above 128 are either meta characters
(if the screen has not been initialized,
or if \fBmeta\fP(3) has been called with a \fBTRUE\fP parameter),
shown in the \fBM\-\fIX\fR notation,
or are displayed as themselves.
In the latter case, the values may not be printable;
this follows the X/Open specification.
.PP
The corresponding \fBwunctrl\fP returns a printable representation of
a complex character \fIc\fP.
.PP
In both \fBunctrl\fP and \fBwunctrl\fP the attributes and color associated
with the character parameter are ignored.
.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 \fIw\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 \fBncurses\fP treats environment variables
when determining the screen size.
.bP
Normally \fBncurses\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),
\fBncurses\fP examines the \fBLINES\fP or \fBCOLUMNS\fP environment variables,
using a value in those to override the results
from the operating system or terminal database.
.IP
\fBNcurses\fP also updates the screen size in response to \fBSIGWINCH\fP,
unless overridden by the \fBLINES\fP or \fBCOLUMNS\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,
\fBncurses\fP modifies the last step in its computation
of screen size as follows:
.bP
checks if the \fBLINES\fP and \fBCOLUMNS\fP environment variables
are set to a number greater than zero.
.bP
for each, \fBncurses\fP updates the corresponding environment variable
with the value that it has obtained via operating system call
or from the terminal database.
.bP
\fBncurses\fP re-fetches the value of the environment variables so that
it is still the environment variables which set the screen size.
.PP
The \fBuse_env\fP and \fBuse_tioctl\fP routines combine as
summarized here:
.PP
.TS
center tab(/);
l l l
_ _ _
lw7 lw7 lw40.
\fBuse_env\fP/\fBuse_tioctl\fP/\fBSummary\fP
TRUE/FALSE/T{
This is the default behavior.
\fBncurses\fP uses operating system calls
unless overridden by $LINES or $COLUMNS environment variables.
T}
TRUE/TRUE/T{
\fBncurses\fP updates $LINES and $COLUMNS based on operating system calls.
T}
FALSE/TRUE/T{
\fBncurses\fP ignores $LINES and $COLUMNS,
uses operating system calls to obtain size.
T}
FALSE/FALSE/T{
\fBncurses\fP relies on the terminal database to determine 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 \fBWINDOW\fP structure,
and its associated character cells.
The format differs between the wide-character (\fBncursesw\fP) and
non-wide (\fBncurses\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 which 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.
This routine should not be used extensively because
padding characters are used rather than a CPU pause.
If no padding character is specified,
this uses \fBnapms\fP to perform the delay.
.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 \fBflushinp\fP, routines that return an integer return \fBERR\fP
upon failure and \fBOK\fP (SVr4 specifies only "an integer value other than
\fBERR\fP") upon successful completion.
.PP
Routines that return pointers return \fBNULL\fP on error.
.PP
X/Open does not define any error conditions.
In this implementation
.RS 3
.TP 5
\fBflushinp\fP
returns an error if the terminal was not initialized.
.TP 5
\fBputwin\fP
returns an error if the associated \fBfwrite\fP calls return an error.
.RE
.SH PORTABILITY
.SS filter
The SVr4 documentation describes the action of \fBfilter\fP only in the vaguest
terms.
The description here is adapted from the XSI Curses standard (which
erroneously fails to describe the disabling of \fBcuu\fP).
.SS keyname
The \fBkeyname\fP function may return the names of user-defined
string capabilities which are defined in the terminfo entry via the \fB\-x\fP
option of \fBtic\fP.
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 \fBuse_extended_names\fP(3) 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 \fBncurses\fP.
They were not supported on Version 7, BSD or System V implementations.
It is recommended that any code depending on \fBncurses\fP extensions
be conditioned using NCURSES_VERSION.
.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 curses sources.
.bP
Most implementations simply dump the binary \fBWINDOW\fP structure to the file.
These include SVr4 curses, NetBSD and PDCurses,
as well as older \fBncurses\fP versions.
This implementation
(as well as the X/Open variant of Solaris curses, dated 1995)
uses textual dumps.
.IP
The implementations which use binary dumps use block-I/O
(the \fBfwrite\fP and \fBfread\fP 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
The XSI Curses standard, Issue 4 describes these functions.
It states that \fBunctrl\fP and \fBwunctrl\fP will return a null pointer if
unsuccessful, but does not define any error conditions.
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 \fBuse_legacy_coding\fP(3) 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 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 \fBuse_legacy_coding\fP(3) function allows the caller to
change the output of \fBunctrl\fP.
.PP
Likewise, the \fBmeta\fP(3) 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 \fBuse_legacy_coding\fP(3) and \fBmeta\fP(3) 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 \fBkeyname\fP is called before initializing curses),
this implementation returns strings \*(``M\-^@\*('', \*(``M\-^A\*('', etc.
.PP
X/Open Curses documents \fBunctrl\fP as declared in \fB<unctrl.h>\fP,
which \fBncurses\fP does.
However, \fBncurses\fP' \fB<curses.h>\fP includes \fB<unctrl.h>\fP,
matching the behavior of SVr4 curses.
Other implementations may not do that.
.SS use_env/use_tioctl
If \fBncurses\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(3)).
This feature of \fBuse_env\fP
is not provided by other implementations of curses.
.SH SEE ALSO
\fBcurses\fP(3),
\fBcurs_initscr\fP(3),
\fBcurs_inopts\fP(3),
\fBcurs_kernel\fP(3),
\fBcurs_scr_dump\fP(3),
\fBcurs_sp_funcs\fP(3),
\fBcurs_variables\fP(3),
\fBlegacy_coding\fP(3).