filter(3ncurses)
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> char *unctrl(chtype c); wchar_t *wunctrl(cchar_t *c); char *keyname(int c); char *key_name(wchar_t w); void filter(void); void nofilter(void); void use_env(bool f); void use_tioctl(bool f); int putwin(WINDOW *win, FILE *filep); WINDOW *getwin(FILE *filep); int delay_output(int ms); int flushinp(void);
DESCRIPTION
unctrl
The unctrl routine returns a character string which is a printable
representation of the character c, ignoring attributes. Control
characters are displayed in the ^X notation. Printing characters are
displayed as is. The corresponding wunctrl returns a printable
representation of a wide character.
keyname/key_name
The keyname routine returns a character string corresponding to the key
c:
* Printable characters are displayed as themselves, e.g., a one-
character string containing the key.
* Control characters are displayed in the ^X notation.
* DEL (character 127) is displayed as ^?.
* Values above 128 are either meta characters (if the screen has not
been initialized, or if meta has been called with a TRUE
parameter), shown in the M-X notation, or are displayed as
themselves. In the latter case, the values may not be printable;
this follows the X/Open specification.
* Values above 256 may be the names of the names of function keys.
* Otherwise (if there is no corresponding name) 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 character string corresponding to
the wide-character value w. The two functions do not return the same
set of strings; the latter returns null where the former would display
a meta character.
filter/nofilter
The filter routine, if used, must be called before initscr or newterm
are called. The effect is that, during those calls, LINES is set to 1;
the capabilities clear, cup, cud, cud1, cuu1, cuu, vpa are disabled;
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 If 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.
Ncurses 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 if 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 which set the screen size.
The use_env and use_tioctl routines combine as summarized here:
use_env use_tioctl Summary
TRUE FALSE This is the default behavior. ncurses
uses operating system calls unless
overridden by $LINES or $COLUMNS
environment variables.
TRUE TRUE ncurses updates $LINES and $COLUMNS
based on operating system calls.
FALSE TRUE ncurses ignores $LINES and $COLUMNS,
uses operating system calls to obtain
size.
FALSE FALSE ncurses relies on the terminal database
to determine 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 which 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.
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 napms to perform the delay.
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, routines that return an integer return ERR upon
failure and OK (SVr4 specifies only "an integer value other than ERR")
upon successful completion.
Routines that return pointers return NULL on error.
X/Open does not define any error conditions. In this implementation
flushinp
returns an error if the terminal was not initialized.
meta returns an error if the terminal was not initialized.
putwin
returns an error if the associated fwrite calls return an
error.
PORTABILITY
filter
The SVr4 documentation describes the action of filter only in the
vaguest terms. The description here is adapted from the XSI Curses
standard (which erroneously fails to describe the disabling of cuu).
keyname
The keyname function may return the names of user-defined string
capabilities which are defined in the terminfo entry via the -x option
of tic. 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 use_extended_names 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
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 and PDCurses, as well as
older ncurses versions. This implementation (as well as the X/Open
variant of Solaris curses, dated 1995) uses textual dumps.
The implementations which use binary dumps use block-I/O (the
fwrite and fread 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
The XSI Curses standard, Issue 4 describes these functions. It states
that unctrl and wunctrl will return a null pointer if unsuccessful, but
does not define any error conditions. 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 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 function allows the caller to
change the output of unctrl.
Likewise, the meta 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 and meta
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.
SEE ALSO
legacy_coding(3NCURSES), ncurses(3NCURSES), initscr(3NCURSES), kernel(3NCURSES), scr_dump(3NCURSES), curses_variables(3NCURSES), legacy_coding(3NCURSES). util(3NCURSES)
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