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.
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(3X) 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
• 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.
The filter routine, if used, must be called before initscr or
newterm are called. Calling filter causes these changes in
• LINES is set to 1;
• the capabilities clear, cud1, cud, cup, cuu1, cuu, vpa are
• 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.
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
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
• 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
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
• 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
The use_env and use_tioctl routines combine as summarized here:
TRUE FALSE This is the default behavior. ncurses
uses operating system calls unless
overridden by $LINES or $COLUMNS
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
FALSE FALSE ncurses relies on the terminal database
to determine size.
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.
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
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, 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
returns an error if the terminal was not initialized.
returns an error if the associated fwrite calls return an
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).
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(3X) function controls whether this data is
loaded when the terminal description is read by the library.
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.
The putwin and getwin functions have several issues with
• 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
• 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.
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(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' <curses.h> includes <unctrl.h>,
matching the behavior of SVr4 curses. Other implementations may
not do that.
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 implementation
This page is part of the ncurses (new curses) project.
Information about the project can be found at
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