by Eric S. Raymond and Zeyd M. Ben-Halim
updates since release 1.9.9e by Thomas Dickey
This document is an introduction to programming with
curses. It is not an exhaustive reference for the
curses Application Programming Interface (API); that role is
filled by the curses manual pages. Rather, it is
intended to help C programmers ease into using the package.
This document is aimed at C applications programmers not yet
specifically familiar with ncurses. If you are already an
experienced curses programmer, you should
nevertheless read the sections on Mouse
Interfacing, Debugging, Compatibility with Older Versions, and Hints, Tips, and Tricks. These will bring you up to
speed on the special features and quirks of the
ncurses implementation. If you are not so
experienced, keep reading.
The curses package is a subroutine library for
terminal-independent screen-painting and input-event handling
which presents a high level screen model to the programmer,
hiding differences between terminal types and doing automatic
optimization of output to change one screen full of text into
another. Curses uses terminfo, which is a database
format that can describe the capabilities of thousands of
different terminals.
The curses API may seem something of an archaism
on UNIX desktops increasingly dominated by X, Motif, and Tcl/Tk.
Nevertheless, UNIX still supports tty lines and X supports
xterm(1); the curses API has the advantage
of (a) back-portability to character-cell terminals, and (b)
simplicity. For an application that does not require bit-mapped
graphics and multiple fonts, an interface implementation using
curses will typically be a great deal simpler and
less expensive than one using an X toolkit.
Historically, the first ancestor of curses was
the routines written to provide screen-handling for the
vi editor; these used the termcap
database facility (both released in 3BSD) for describing terminal
capabilities. These routines were abstracted into a documented
library and first released with the early BSD UNIX versions. All
of this work was done by students at the University of California
(Berkeley campus). The curses library was first published in
4.0BSD, a year after 3BSD (i.e., late 1980).
After graduation, one of those students went to work at
AT&T Bell Labs, and made an improved termcap
library called terminfo (i.e.,
“libterm”), and adapted the curses library to use
this. That was subsequently released in System V Release 2 (early
1984). Thereafter, other developers added to the curses and
terminfo libraries. For instance, a student at Cornell University
wrote an improved terminfo library as well as a tool
(tic) to compile the terminal descriptions. As a
general rule, AT&T did not identify the developers in the
source-code or documentation; the tic and
infocmp programs are the exceptions.
System V Release 3 (System III UNIX) from Bell Labs featured a
rewritten and much-improved curses library, along
with the tic program (late 1986).
To recap, terminfo is based on Berkeley's termcap database,
but contains a number of improvements and extensions.
Parameterized capabilities strings were introduced, making it
possible to describe multiple video attributes, and colors and to
handle far more unusual terminals than possible with termcap. In
the later AT&T System V releases, curses evolved
to use more facilities and offer more capabilities, going far
beyond BSD curses in power and flexibility.
This document describes ncurses, a free
implementation of the System V curses API with some
clearly marked extensions. It includes the following System V
curses features:
Also, this package makes use of the insert and delete line and character features of terminals so equipped, and determines how to optimally use these features with no help from the programmer. It allows arbitrary combinations of video attributes to be displayed, even on terminals that leave “magic cookies” on the screen to mark changes in attributes.
The ncurses package can also capture and use
event reports from a mouse in some environments (notably, xterm
under the X window system). This document includes tips for using
the mouse.
The ncurses package was originated by Pavel
Curtis. The original maintainer of this package is Zeyd Ben-Halim
<zmbenhal@netcom.com>. Eric S. Raymond
<esr@snark.thyrsus.com> wrote many of the new features in
versions after 1.8.1 and wrote most of this introduction.
Jürgen Pfeifer wrote all of the menu and forms code as well
as the Ada95 binding.
Ongoing work is being done by Thomas Dickey
(maintainer). Contact the current maintainers at bug-ncurses@gnu.org.
This document also describes the panels extension library, similarly modeled on the SVr4 panels facility. This library allows you to associate backing store with each of a stack or deck of overlapping windows, and provides operations for moving windows around in the stack that change their visibility in the natural way (handling window overlaps).
Finally, this document describes in detail the menus and forms extension libraries, also cloned from System V, which support easy construction and sequences of menus and fill-in forms.
In this document, the following terminology is used with reasonable consistency:
stdscr, is automatically provided for the
programmer.In order to use the library, it is necessary to have certain types and variables defined. Therefore, the programmer must have a line:
#include <curses.h>
at the top of the program source. The screen package uses the
Standard I/O library, so <curses.h> includes
<stdio.h>. <curses.h> also
includes <termios.h>,
<termio.h>, or <sgtty.h>
depending on your system. It is redundant (but harmless) for the
programmer to do these includes, too. In linking with
curses you need to have -lncurses in
your LDFLAGS or on the command line. There is no need for any
other libraries.
In order to update the screen optimally, it is necessary for
the routines to know what the screen currently looks like and
what the programmer wants it to look like next. For this purpose,
a data type (structure) named WINDOW is defined which describes a
window image to the routines, including its starting position on
the screen (the (y, x) coordinates of the upper left hand corner)
and its size. One of these (called curscr, for
current screen) is a screen image of what the terminal currently
looks like. Another screen (called stdscr, for
standard screen) is provided by default to make changes on.
A window is a purely internal representation. It is used to build and store a potential image of a portion of the terminal. It does not bear any necessary relation to what is really on the terminal screen; it is more like a scratchpad or write buffer.
To make the section of physical screen corresponding to a
window reflect the contents of the window structure, the routine
refresh() (or wrefresh() if the window
is not stdscr) is called.
A given physical screen section may be within the scope of any number of overlapping windows. Also, changes can be made to windows in any order, without regard to motion efficiency. Then, at will, the programmer can effectively say “make it look like this,” and let the package implementation determine the most efficient way to repaint the screen.
As hinted above, the routines can use several windows, but two
are automatically given: curscr, which knows what
the terminal looks like, and stdscr, which is what
the programmer wants the terminal to look like next. The user
should never actually access curscr directly.
Changes should be made to through the API, and then the routine
refresh() (or wrefresh()) called.
Many functions are defined to use stdscr as a
default screen. For example, to add a character to
stdscr, one calls addch() with the
desired character as argument. To write to a different window.
use the routine waddch() (for
window-specific addch()) is provided. This
convention of prepending function names with a “w”
when they are to be applied to specific windows is consistent.
The only routines which do not follow it are those for which a
window must always be specified.
In order to move the current (y, x) coordinates from one point
to another, the routines move() and
wmove() are provided. However, it is often desirable
to first move and then perform some I/O operation. In order to
avoid clumsiness, most I/O routines can be preceded by the prefix
“mv” and the desired (y, x) coordinates prepended to
the arguments to the function. For example, the calls
move(y, x);
addch(ch);
can be replaced by
mvaddch(y, x, ch);
and
wmove(win, y, x);
waddch(win, ch);
can be replaced by
mvwaddch(win, y, x, ch);
Note that the window description pointer (win) comes before the added (y, x) coordinates. If a function requires a window pointer, it is always the first parameter passed.
The curses library sets some variables describing
the terminal capabilities.
type name description
------------------------------------------------------------------
int LINES number of lines on the terminal
int COLS number of columns on the terminal
The curses.h also introduces some
#define constants and types of general
usefulness:
bool
bool doneit;)TRUE
FALSE
ERR
OK
Now we describe how to actually use the screen package. In it,
we assume all updating, reading, etc. is applied to
stdscr. These instructions will work on any window,
providing you change the function names and parameters as
mentioned above.
Here is a sample program to motivate the discussion:
#include <stdlib.h>
#include <curses.h>
#include <signal.h>
static void finish(int sig);
int
main(int argc, char *argv[])
{
int num = 0;
/* initialize your non-curses data structures here */
(void) signal(SIGINT, finish); /* arrange interrupts to terminate */
(void) initscr(); /* initialize the curses library */
keypad(stdscr, TRUE); /* enable keyboard mapping */
(void) nonl(); /* tell curses not to do NL->CR/NL on output */
(void) cbreak(); /* take input chars one at a time, no wait for \n */
(void) echo(); /* echo input - in color */
if (has_colors())
{
start_color();
/*
* Simple color assignment, often all we need. Color pair 0 cannot
* be redefined. This example uses the same value for the color
* pair as for the foreground color, though of course that is not
* necessary:
*/
init_pair(1, COLOR_RED, COLOR_BLACK);
init_pair(2, COLOR_GREEN, COLOR_BLACK);
init_pair(3, COLOR_YELLOW, COLOR_BLACK);
init_pair(4, COLOR_BLUE, COLOR_BLACK);
init_pair(5, COLOR_CYAN, COLOR_BLACK);
init_pair(6, COLOR_MAGENTA, COLOR_BLACK);
init_pair(7, COLOR_WHITE, COLOR_BLACK);
}
for (;;)
{
int c = getch(); /* refresh, accept single keystroke of input */
attrset(COLOR_PAIR(num % 8));
num++;
/* process the command keystroke */
}
finish(0); /* we are done */
}
static void finish(int sig)
{
endwin();
/* do your non-curses wrapup here */
exit(0);
}
In order to use the screen package, the routines must know
about terminal characteristics, and the space for
curscr and stdscr must be allocated.
These function initscr() does both these things.
Since it must allocate space for the windows, it can overflow
memory when attempting to do so. On the rare occasions this
happens, initscr() will terminate the program with
an error message. initscr() must always be called
before any of the routines which affect windows are used. If it
is not, the program will core dump as soon as either
curscr or stdscr are referenced.
However, it is usually best to wait to call it until after you
are sure you will need it, like after checking for startup
errors. Terminal status changing routines like nl()
and cbreak() should be called after
initscr().
Once the screen windows have been allocated, you can set them
up for your program. If you want to, say, allow a screen to
scroll, use scrollok(). If you want the cursor to be
left in place after the last change, use leaveok().
If this is not done, refresh() will move the cursor
to the window's current (y, x) coordinates after updating it.
You can create new windows of your own using the functions
newwin(), derwin(), and
subwin(). The routine delwin() will
allow you to get rid of old windows. All the options described
above can be applied to any window.
Now that we have set things up, we will want to actually
update the terminal. The basic functions used to change what will
go on a window are addch() and move().
addch() adds a character at the current (y, x)
coordinates. move() changes the current (y, x)
coordinates to whatever you want them to be. It returns
ERR if you try to move off the window. As mentioned
above, you can combine the two into mvaddch() to do
both things at once.
The other output functions, such as addstr() and
printw(), all call addch() to add
characters to the window.
After you have put on the window what you want there, when you
want the portion of the terminal covered by the window to be made
to look like it, you must call refresh(). In order
to optimize finding changes, refresh() assumes that
any part of the window not changed since the last
refresh() of that window has not been changed on the
terminal, i.e., that you have not refreshed a portion of the
terminal with an overlapping window. If this is not the case, the
routine touchwin() is provided to make it look like
the entire window has been changed, thus making
refresh() check the whole subsection of the terminal
for changes.
If you call wrefresh() with curscr
as its argument, it will make the screen look like
curscr thinks it looks like. This is useful for
implementing a command which would redraw the screen in case it
get messed up.
The complementary function to addch() is
getch() which, if echo is set, will call
addch() to echo the character. Since the screen
package needs to know what is on the terminal at all times, if
characters are to be echoed, the tty must be in raw or cbreak
mode. Since initially the terminal has echoing enabled and is in
ordinary “cooked” mode, one or the other has to
changed before calling getch(); otherwise, the
program's output will be unpredictable.
When you need to accept line-oriented input in a window, the
functions wgetstr() and friends are available. There
is even a wscanw() function that can do
scanf()(3)-style multi-field parsing on window
input. These pseudo-line-oriented functions turn on echoing while
they execute.
The example code above uses the call keypad(stdscr,
TRUE) to enable support for function-key mapping. With
this feature, the getch() code watches the input
stream for character sequences that correspond to arrow and
function keys. These sequences are returned as pseudo-character
values. The #define values returned are listed in
the curses.h The mapping from sequences to
#define values is determined by key_
capabilities in the terminal's terminfo entry.
The addch() function (and some others, including
box() and border()) can accept some
pseudo-character arguments which are specially defined by
ncurses. These are #define values set
up in the curses.h header; see there for a complete
list (look for the prefix ACS_).
The most useful of the ACS defines are the forms-drawing
characters. You can use these to draw boxes and simple graphs on
the screen. If the terminal does not have such characters,
curses.h will map them to a recognizable (though
ugly) set of ASCII defaults.
The ncurses package supports screen highlights
including standout, reverse-video, underline, and blink. It also
supports color, which is treated as another kind of
highlight.
Highlights are encoded, internally, as high bits of the
pseudo-character type (chtype) that
curses.h uses to represent the contents of a screen
cell. See the curses.h header file for a complete
list of highlight mask values (look for the prefix
A_).
There are two ways to make highlights. One is to logical-or
the value of the highlights you want into the character argument
of an addch() call, or any other output call that
takes a chtype argument.
The other is to set the current-highlight value. This is
logical-ORed with any highlight you specify the first
way. You do this with the functions attron(),
attroff(), and attrset(); see the
manual pages for details. Color is a special kind of highlight.
The package actually thinks in terms of color pairs, combinations
of foreground and background colors. The sample code above sets
up eight color pairs, all of the guaranteed-available colors on
black. Note that each color pair is, in effect, given the name of
its foreground color. Any other range of eight non-conflicting
values could have been used as the first arguments of the
init_pair() values.
Once you have done an init_pair() that creates
color-pair N, you can use COLOR_PAIR(N) as a
highlight that invokes that particular color combination. Note
that COLOR_PAIR(N), for constant N, is itself a
compile-time constant and can be used in initializers.
The ncurses library also provides a mouse
interface.
NOTE: this facility is specific to
ncurses, it is not part of either the XSI Curses
standard, nor of System V Release 4, nor BSD curses. System V
Release 4 curses contains code with similar interface
definitions, however it is not documented. Other than by
disassembling the library, we have no way to determine exactly
how that mouse code works. Thus, we recommend that you wrap
mouse-related code in an #ifdef using the feature macro
NCURSES_MOUSE_VERSION so it will not be compiled and linked on
non-ncurses systems.
Presently, mouse event reporting works in the following environments:
gpm(1),
Alessandro Rubini's mouse server.The mouse interface is very simple. To activate it, you use
the function mousemask(), passing it as first
argument a bit-mask that specifies what kinds of events you want
your program to be able to see. It will return the bit-mask of
events that actually become visible, which may differ from the
argument if the mouse device is not capable of reporting some of
the event types you specify.
Once the mouse is active, your application's command loop
should watch for a return value of KEY_MOUSE from
wgetch(). When you see this, a mouse event report
has been queued. To pick it off the queue, use the function
getmouse() (you must do this before the next
wgetch(), otherwise another mouse event might come
in and make the first one inaccessible).
Each call to getmouse() fills a structure (the
address of which you will pass it) with mouse event data. The
event data includes zero-origin, screen-relative character-cell
coordinates of the mouse pointer. It also includes an event mask.
Bits in this mask will be set, corresponding to the event type
being reported.
The mouse structure contains two additional fields which may be significant in the future as ncurses interfaces to new kinds of pointing device. In addition to x and y coordinates, there is a slot for a z coordinate; this might be useful with touch-screens that can return a pressure or duration parameter. There is also a device ID field, which could be used to distinguish between multiple pointing devices.
The class of visible events may be changed at any time via
mousemask(). Events that can be reported include
presses, releases, single-, double- and triple-clicks (you can
set the maximum button-down time for clicks). If you do not make
clicks visible, they will be reported as press-release pairs. In
some environments, the event mask may include bits reporting the
state of shift, alt, and ctrl keys on the keyboard during the
event.
A function to check whether a mouse event fell within a given window is also supplied. You can use this to see whether a given window should consider a mouse event relevant to it.
Because mouse event reporting will not be available in all
environments, it would be unwise to build ncurses
applications that require the use of a mouse. Rather,
you should use the mouse as a shortcut for point-and-shoot
commands your application would normally accept from the
keyboard. Two of the test games in the ncurses
distribution (bs and knight) contain
code that illustrates how this can be done.
See the manual page curs_mouse(3X) for full
details of the mouse-interface functions.
In order to clean up after the ncurses routines,
the routine endwin() is provided. It restores tty
modes to what they were when initscr() was first
called, and moves the cursor down to the lower-left corner. Thus,
anytime after the call to initscr, endwin() should
be called before exiting.
We describe the detailed behavior of some important curses functions here, as a supplement to the manual page descriptions.
initscr()
initscr(). This will determine the terminal type
and initialize curses data structures. initscr()
also arranges that the first call to refresh()
will clear the screen. If an error occurs a message is written
to standard error and the program exits. Otherwise it returns a
pointer to stdscr. A few functions may be called before initscr
(slk_init(), filter(),
ripoffline(), use_env(), and, if you
are using multiple terminals, newterm().)endwin()
endwin()
before exiting or shelling out of the program. This function
will restore tty modes, move the cursor to the lower left
corner of the screen, reset the terminal into the proper
non-visual mode. Calling refresh() or
doupdate() after a temporary escape from the
program will restore the ncurses screen from before the
escape.newterm(type, ofp, ifp)
newterm() instead of initscr().
newterm() should be called once for each terminal.
It returns a variable of type SCREEN * which
should be saved as a reference to that terminal. (NOTE: a
SCREEN variable is not a screen in the sense we are
describing in this introduction, but a collection of parameters
used to assist in optimizing the display.) The arguments are
the type of the terminal (a string) and FILE
pointers for the output and input of the terminal. If type is
NULL then the environment variable $TERM is used.
endwin() should called once at wrapup time for
each terminal opened using this function.set_term(new)
newterm(). The screen
reference for the new terminal is passed as the parameter. The
previous terminal is returned by the function. All other calls
affect only the current terminal.delscreen(sp)
newterm(); deallocates the data
structures associated with a given SCREEN
reference.refresh() and wrefresh(win)wrefresh() copies the named window to
the physical terminal screen, taking into account what is
already there in order to do optimizations.
refresh() does a refresh of stdscr.
Unless leaveok() has been enabled, the physical
cursor of the terminal is left at the location of the window's
cursor.doupdate() and
wnoutrefresh(win)wnoutrefresh()), and then calling the routine to
update the screen (doupdate()). If the programmer
wishes to output several windows at once, a series of calls to
wrefresh will result in alternating calls to
wnoutrefresh() and doupdate(),
causing several bursts of output to the screen. By calling
wnoutrefresh() for each window, it is then
possible to call doupdate() once, resulting in
only one burst of output, with fewer total characters
transmitted (this also avoids a visually annoying flicker at
each update).setupterm(term, filenum, errret)
term is
the character string representing the name of the terminal
being used. filenum is the UNIX file descriptor
of the terminal to be used for output. errret is
a pointer to an integer, in which a success or failure
indication is returned. The values returned can be 1 (all is
well), 0 (no such terminal), or -1 (some problem locating the
terminfo database).
The value of term can be given as NULL, which
will cause the value of TERM in the environment
to be used. The errret pointer can also be given
as NULL, meaning no error code is wanted. If
errret is defaulted, and something goes wrong,
setupterm() will print an appropriate error
message and exit, rather than returning. Thus, a simple
program can call setupterm(0, 1, 0) and not worry about
initialization errors.
After the call to setupterm(), the global
variable cur_term is set to point to the current
structure of terminal capabilities. By calling
setupterm() for each terminal, and saving and
restoring cur_term, it is possible for a program
to use two or more terminals at once.
Setupterm() also stores the names section of the
terminal description in the global character array
ttytype[]. Subsequent calls to
setupterm() will overwrite this array, so you
will have to save it yourself if need be.
NOTE: These functions are not part of the standard curses API!
trace()
TRACE_
defines in the curses.h file for details. (It is
also possible to set a trace level by assigning a trace level
value to the environment variable
NCURSES_TRACE)._tracef()
printf(), only it outputs a newline after the end
of arguments. The output goes to a file called
trace in the current directory.Trace logs can be difficult to interpret due to the sheer
volume of data dumped in them. There is a script called
tracemunch included with the
ncurses distribution that can alleviate this problem
somewhat; it compacts long sequences of similar operations into
more succinct single-line pseudo-operations. These pseudo-ops can
be distinguished by the fact that they are named in capital
letters.
The ncurses manual pages are a complete reference
for this library. In the remainder of this document, we discuss
various useful methods that may not be obvious from the manual
page descriptions.
If you find yourself thinking you need to use
noraw() or nocbreak(), think again and
move carefully. It is probably better design to use
getstr() or one of its relatives to simulate cooked
mode. The noraw() and nocbreak()
functions try to restore cooked mode, but they may end up
clobbering some control bits set before you started your
application. Also, they have always been poorly documented, and
are likely to hurt your application's usability with other curses
libraries.
Bear in mind that refresh() is a synonym for
wrefresh(stdscr). Do not try to mix use of
stdscr with use of windows declared by
newwin(); a refresh() call will blow
them off the screen. The right way to handle this is to use
subwin(), or not touch stdscr at all
and tile your screen with declared windows which you then
wnoutrefresh() somewhere in your program event loop,
with a single doupdate() call to trigger actual
repainting.
You are much less likely to run into problems if you design
your screen layouts to use tiled rather than overlapping windows.
Historically, curses support for overlapping windows has been
weak, fragile, and poorly documented. The ncurses
library is not yet an exception to this rule.
There is a panels library included in the ncurses
distribution that does a pretty good job of strengthening the
overlapping-windows facilities.
Try to avoid using the global variables LINES and COLS. Use
getmaxyx() on the stdscr context
instead. Reason: your code may be ported to run in an environment
with window resizes, in which case several screens could be open
with different sizes.
Sometimes you will want to write a program that spends most of
its time in screen mode, but occasionally returns to ordinary
“cooked” mode. A common reason for this is to support
shell-out. This behavior is simple to arrange in
ncurses.
To leave ncurses mode, call endwin()
as you would if you were intending to terminate the program. This
will take the screen back to cooked mode; you can do your
shell-out. When you want to return to ncurses mode,
simply call refresh() or doupdate().
This will repaint the screen.
There is a boolean function, isendwin(), which
code can use to test whether ncurses screen mode is
active. It returns TRUE in the interval between an
endwin() call and the following
refresh(), FALSE otherwise.
Here is some sample code for shellout:
addstr("Shelling out...");
def_prog_mode(); /* save current tty modes */
endwin(); /* restore original tty modes */
system("sh"); /* run shell */
addstr("returned.\n"); /* prepare return message */
refresh(); /* restore save modes, repaint screen */
A resize operation in X sends SIGWINCH to the
application running under xterm. The easiest way to handle
SIGWINCH is to do an endwin, followed
by an refresh and a screen repaint you code
yourself. The refresh will pick up the new screen
size from the xterm's environment.
That is the standard way, of course (it even works with some
vendor's curses implementations). Its drawback is that it clears
the screen to reinitialize the display, and does not resize
subwindows which must be shrunk. Ncurses provides an
extension which works better, the resizeterm
function. That function ensures that all windows are limited to
the new screen dimensions, and pads stdscr with
blanks if the screen is larger.
The ncurses library provides a SIGWINCH signal
handler, which pushes a KEY_RESIZE via the wgetch()
calls. When ncurses returns that code, it calls
resizeterm to update the size of the standard
screen's window, repainting that (filling with blanks or
truncating as needed). It also resizes other windows, but its
effect may be less satisfactory because it cannot know how you
want the screen re-painted. You will usually have to write
special-purpose code to handle KEY_RESIZE
yourself.
The initscr() function actually calls a function
named newterm() to do most of its work. If you are
writing a program that opens multiple terminals, use
newterm() directly.
For each call, you will have to specify a terminal type and a
pair of file pointers; each call will return a screen reference,
and stdscr will be set to the last one allocated.
You will switch between screens with the set_term
call. Note that you will also have to call
def_shell_mode and def_prog_mode on
each tty yourself.
Sometimes you may want to write programs that test for the
presence of various capabilities before deciding whether to go
into ncurses mode. An easy way to do this is to call
setupterm(), then use the functions
tigetflag(), tigetnum(), and
tigetstr() to do your testing.
A particularly useful case of this often comes up when you
want to test whether a given terminal type should be treated as
“smart” (cursor-addressable) or “stupid”.
The right way to test this is to see if the return value of
tigetstr("cup") is non-NULL. Alternatively, you can
include the term.h file and test the value of the
macro cursor_address.
Use the addchstr() family of functions for fast
screen-painting of text when you know the text does not contain
any control characters. Try to make attribute changes infrequent
on your screens. Do not use the immedok()
option!
The wresize() function allows you to resize a
window in place. The associated resizeterm()
function simplifies the construction of SIGWINCH handlers, for resizing all windows.
The define_key() function allows you to define at
runtime function-key control sequences which are not in the
terminal description. The keyok() function allows
you to temporarily enable or disable interpretation of any
function-key control sequence.
The use_default_colors() function allows you to
construct applications which can use the terminal's default
foreground and background colors as an additional "default"
color. Several terminal emulators support this feature, which is
based on ISO 6429.
Ncurses supports up 16 colors, unlike SVr4 curses which defines only 8. While most terminals which provide color allow only 8 colors, about a quarter (including XFree86 xterm) support 16 colors.
Despite our best efforts, there are some differences between
ncurses and the (undocumented!) behavior of older
curses implementations. These arise from ambiguities or omissions
in the documentation of the API.
If you define two windows A and B that overlap, and then
alternately scribble on and refresh them, the changes made to the
overlapping region under historic curses versions
were often not documented precisely.
To understand why this is a problem, remember that screen updates are calculated between two representations of the entire display. The documentation says that when you refresh a window, it is first copied to the virtual screen, and then changes are calculated to update the physical screen (and applied to the terminal). But "copied to" is not very specific, and subtle differences in how copying works can produce different behaviors in the case where two overlapping windows are each being refreshed at unpredictable intervals.
What happens to the overlapping region depends on what
wnoutrefresh() does with its argument -- what
portions of the argument window it copies to the virtual screen.
Some implementations do "change copy", copying down only
locations in the window that have changed (or been marked changed
with wtouchln() and friends). Some implementations
do "entire copy", copying all window locations to the
virtual screen whether or not they have changed.
The ncurses library itself has not always been
consistent on this score. Due to a bug, versions 1.8.7 to 1.9.8a
did entire copy. Versions 1.8.6 and older, and versions 1.9.9 and
newer, do change copy.
For most commercial curses implementations, it is not
documented and not known for sure (at least not to the
ncurses maintainers) whether they do change copy or
entire copy. We know that System V release 3 curses has logic in
it that looks like an attempt to do change copy, but the
surrounding logic and data representations are sufficiently
complex, and our knowledge sufficiently indirect, that it is hard
to know whether this is reliable. It is not clear what the SVr4
documentation and XSI standard intend. The XSI Curses standard
barely mentions wnoutrefresh(); the SVr4 documents seem to be
describing entire-copy, but it is possible with some effort and
straining to read them the other way.
It might therefore be unwise to rely on either behavior in
programs that might have to be linked with other curses
implementations. Instead, you can do an explicit
touchwin() before the wnoutrefresh()
call to guarantee an entire-contents copy anywhere.
The really clean way to handle this is to use the panels
library. If, when you want a screen update, you do
update_panels(), it will do all the necessary
wnoutrefresh() calls for whatever panel stacking
order you have defined. Then you can do one
doupdate() and there will be a single burst
of physical I/O that will do all your updates.
If you have been using a very old versions of
ncurses (1.8.7 or older) you may be surprised by the
behavior of the erase functions. In older versions, erased areas
of a window were filled with a blank modified by the window's
current attribute (as set by wattrset(),
wattron(), wattroff() and
friends).
In newer versions, this is not so. Instead, the attribute of
erased blanks is normal unless and until it is modified by the
functions bkgdset() or wbkgdset().
This change in behavior conforms ncurses to
System V Release 4 and the XSI Curses standard.
The ncurses library is intended to be base-level
conformant with the XSI Curses standard from X/Open. Many
extended-level features (in fact, almost all features not
directly concerned with wide characters and internationalization)
are also supported.
One effect of XSI conformance is the change in behavior described under "Background Erase -- Compatibility with Old Versions".
Also, ncurses meets the XSI requirement that
every macro entry point have a corresponding function which may
be linked (and will be prototype-checked) if the macro definition
is disabled with #undef.
The ncurses library by itself provides good
support for screen displays in which the windows are tiled
(non-overlapping). In the more general case that windows may
overlap, you have to use a series of wnoutrefresh()
calls followed by a doupdate(), and be careful about
the order you do the window refreshes in. It has to be
bottom-upwards, otherwise parts of windows that should be
obscured will show through.
When your interface design is such that windows may dive deeper into the visibility stack or pop to the top at runtime, the resulting book-keeping can be tedious and difficult to get right. Hence the panels library.
The panel library first appeared in AT&T
System V. The version documented here is the panel
code distributed with ncurses.
Your panels-using modules must import the panels library declarations with
#include <panel.h>
and must be linked explicitly with the panels library using an
-lpanel argument. Note that they must also link the
ncurses library with -lncurses. Many
linkers are two-pass and will accept either order, but it is
still good practice to put -lpanel first and
-lncurses second.
A panel object is a window that is implicitly treated as part
of a deck including all other panel objects. The deck
has an implicit bottom-to-top visibility order. The panels
library includes an update function (analogous to
refresh()) that displays all panels in the deck in
the proper order to resolve overlaps. The standard window,
stdscr, is considered below all panels.
Details on the panels functions are available in the man pages. We will just hit the highlights here.
You create a panel from a window by calling
new_panel() on a window pointer. It then becomes the
top of the deck. The panel's window is available as the value of
panel_window() called with the panel pointer as
argument.
You can delete a panel (removing it from the deck) with
del_panel. This will not deallocate the associated
window; you have to do that yourself. You can replace a panel's
window with a different window by calling
replace_window. The new window may be of different
size; the panel code will re-compute all overlaps. This operation
does not change the panel's position in the deck.
To move a panel's window, use move_panel(). The
mvwin() function on the panel's window is not
sufficient because it does not update the panels library's
representation of where the windows are. This operation leaves
the panel's depth, contents, and size unchanged.
Two functions (top_panel(),
bottom_panel()) are provided for rearranging the
deck. The first pops its argument window to the top of the deck;
the second sends it to the bottom. Either operation leaves the
panel's screen location, contents, and size unchanged.
The function update_panels() does all the
wnoutrefresh() calls needed to prepare for
doupdate() (which you must call yourself,
afterwards).
Typically, you will want to call update_panels()
and doupdate() just before accepting command input,
once in each cycle of interaction with the user. If you call
update_panels() after each and every panel write,
you will generate a lot of unnecessary refresh activity and
screen flicker.
You should not mix wnoutrefresh() or
wrefresh() operations with panels code; this will
work only if the argument window is either in the top panel or
unobscured by any other panels.
The stsdcr window is a special case. It is
considered below all panels. Because changes to panels may
obscure parts of stdscr, though, you should call
update_panels() before doupdate() even
when you only change stdscr.
Note that wgetch automatically calls
wrefresh. Therefore, before requesting input from a
panel window, you need to be sure that the panel is totally
unobscured.
There is presently no way to display changes to one obscured panel without repainting all panels.
It is possible to remove a panel from the deck temporarily;
use hide_panel for this. Use
show_panel() to render it visible again. The
predicate function panel_hidden tests whether or not
a panel is hidden.
The panel_update code ignores hidden panels. You
cannot do top_panel() or bottom_panel
on a hidden panel(). Other panels operations are applicable.
It is possible to navigate the deck using the functions
panel_above() and panel_below. Handed a
panel pointer, they return the panel above or below that panel.
Handed NULL, they return the bottom-most or top-most
panel.
Every panel has an associated user pointer, not used by the
panel code, to which you can attach application data. See the man
page documentation of set_panel_userptr() and
panel_userptr for details.
A menu is a screen display that assists the user to choose
some subset of a given set of items. The menu
library is a curses extension that supports easy programming of
menu hierarchies with a uniform but flexible interface.
The menu library first appeared in AT&T
System V. The version documented here is the menu
code distributed with ncurses.
Your menu-using modules must import the menu library declarations with
#include <menu.h>
and must be linked explicitly with the menus library using an
-lmenu argument. Note that they must also link the
ncurses library with -lncurses. Many
linkers are two-pass and will accept either order, but it is
still good practice to put -lmenu first and
-lncurses second.
The menus created by this library consist of collections of items including a name string part and a description string part. To make menus, you create groups of these items and connect them with menu frame objects.
The menu can then by posted, that is written to an associated window. Actually, each menu has two associated windows; a containing window in which the programmer can scribble titles or borders, and a subwindow in which the menu items proper are displayed. If this subwindow is too small to display all the items, it will be a scrollable viewport on the collection of items.
A menu may also be unposted (that is, undisplayed), and finally freed to make the storage associated with it and its items available for re-use.
The general flow of control of a menu program looks like this:
curses.new_item().new_menu().post_menu().unpost_menu().free_menu().free_item().curses.Menus may be multi-valued or (the default) single-valued (see
the manual page menu_opts(3x) to see how to change
the default). Both types always have a current
item.
From a single-valued menu you can read the selected value
simply by looking at the current item. From a multi-valued menu,
you get the selected set by looping through the items applying
the item_value() predicate function. Your
menu-processing code can use the function
set_item_value() to flag the items in the select
set.
Menu items can be made unselectable using
set_item_opts() or item_opts_off() with
the O_SELECTABLE argument. This is the only option
so far defined for menus, but it is good practice to code as
though other option bits might be on.
The menu library calculates a minimum display size for your window, based on the following variables:
The function set_menu_format() allows you to set
the maximum size of the viewport or menu page that
will be used to display menu items. You can retrieve any format
associated with a menu with menu_format(). The
default format is rows=16, columns=1.
The actual menu page may be smaller than the format size. This depends on the item number and size and whether O_ROWMAJOR is on. This option (on by default) causes menu items to be displayed in a “raster-scan” pattern, so that if more than one item will fit horizontally the first couple of items are side-by-side in the top row. The alternative is column-major display, which tries to put the first several items in the first column.
As mentioned above, a menu format not large enough to allow all items to fit on-screen will result in a menu display that is vertically scrollable.
You can scroll it with requests to the menu driver, which will be described in the section on menu input handling.
Each menu has a mark string used to visually tag
selected items; see the menu_mark(3x) manual page
for details. The mark string length also influences the menu page
size.
The function scale_menu() returns the minimum
display size that the menu code computes from all these factors.
There are other menu display attributes including a select
attribute, an attribute for selectable items, an attribute for
unselectable items, and a pad character used to separate item
name text from description text. These have reasonable defaults
which the library allows you to change (see the
menu_attribs(3x) manual page.
Each menu has, as mentioned previously, a pair of associated windows. Both these windows are painted when the menu is posted and erased when the menu is unposted.
The outer or frame window is not otherwise touched by the menu routines. It exists so the programmer can associate a title, a border, or perhaps help text with the menu and have it properly refreshed or erased at post/unpost time. The inner window or subwindow is where the current menu page is displayed.
By default, both windows are stdscr. You can set
them with the functions in menu_win(3x).
When you call post_menu(), you write the menu to
its subwindow. When you call unpost_menu(), you
erase the subwindow, However, neither of these actually modifies
the screen. To do that, call wrefresh() or some
equivalent.
The main loop of your menu-processing code should call
menu_driver() repeatedly. The first argument of this
routine is a menu pointer; the second is a menu command code. You
should write an input-fetching routine that maps input characters
to menu command codes, and pass its output to
menu_driver(). The menu command codes are fully
documented in menu_driver(3x).
The simplest group of command codes is
REQ_NEXT_ITEM, REQ_PREV_ITEM,
REQ_FIRST_ITEM, REQ_LAST_ITEM,
REQ_UP_ITEM, REQ_DOWN_ITEM,
REQ_LEFT_ITEM, REQ_RIGHT_ITEM. These
change the currently selected item. These requests may cause
scrolling of the menu page if it only partially displayed.
There are explicit requests for scrolling which also change
the current item (because the select location does not change,
but the item there does). These are REQ_SCR_DLINE,
REQ_SCR_ULINE, REQ_SCR_DPAGE, and
REQ_SCR_UPAGE.
The REQ_TOGGLE_ITEM selects or deselects the
current item. It is for use in multi-valued menus; if you use it
with O_ONEVALUE on, you will get an error return
(E_REQUEST_DENIED).
Each menu has an associated pattern buffer. The
menu_driver() logic tries to accumulate printable
ASCII characters passed in in that buffer; when it matches a
prefix of an item name, that item (or the next matching item) is
selected. If appending a character yields no new match, that
character is deleted from the pattern buffer, and
menu_driver() returns E_NO_MATCH.
Some requests change the pattern buffer directly:
REQ_CLEAR_PATTERN, REQ_BACK_PATTERN,
REQ_NEXT_MATCH, REQ_PREV_MATCH. The
latter two are useful when pattern buffer input matches more than
one item in a multi-valued menu.
Each successful scroll or item navigation request clears the
pattern buffer. It is also possible to set the pattern buffer
explicitly with set_menu_pattern().
Finally, menu driver requests above the constant
MAX_COMMAND are considered application-specific
commands. The menu_driver() code ignores them and
returns E_UNKNOWN_COMMAND.
Various menu options can affect the processing and visual
appearance and input processing of menus. See menu_opts(3x)
for details.
It is possible to change the current item from application
code; this is useful if you want to write your own navigation
requests. It is also possible to explicitly set the top row of
the menu display. See mitem_current(3x). If your
application needs to change the menu subwindow cursor for any
reason, pos_menu_cursor() will restore it to the
correct location for continuing menu driver processing.
It is possible to set hooks to be called at menu
initialization and wrapup time, and whenever the selected item
changes. See menu_hook(3x).
Each item, and each menu, has an associated user pointer on
which you can hang application data. See
mitem_userptr(3x) and
menu_userptr(3x).
The form library is a curses extension that
supports easy programming of on-screen forms for data entry and
program control.
The form library first appeared in AT&T
System V. The version documented here is the form
code distributed with ncurses.
Your form-using modules must import the form library declarations with
#include <form.h>
and must be linked explicitly with the forms library using an
-lform argument. Note that they must also link the
ncurses library with -lncurses. Many
linkers are two-pass and will accept either order, but it is
still good practice to put -lform first and
-lncurses second.
A form is a collection of fields; each field may be either a label (explanatory text) or a data-entry location. Long forms may be segmented into pages; each entry to a new page clears the screen.
To make forms, you create groups of fields and connect them with form frame objects; the form library makes this relatively simple.
Once defined, a form can be posted, that is written to an associated window. Actually, each form has two associated windows; a containing window in which the programmer can scribble titles or borders, and a subwindow in which the form fields proper are displayed.
As the form user fills out the posted form, navigation and
editing keys support movement between fields, editing keys
support modifying field, and plain text adds to or changes data
in a current field. The form library allows you (the forms
designer) to bind each navigation and editing key to any
keystroke accepted by curses Fields may have
validation conditions on them, so that they check input data for
type and value. The form library supplies a rich set of
pre-defined field types, and makes it relatively easy to define
new ones.
Once its transaction is completed (or aborted), a form may be unposted (that is, undisplayed), and finally freed to make the storage associated with it and its items available for re-use.
The general flow of control of a form program looks like this:
curses.new_field().new_form().post_form().unpost_form().free_form().free_field().curses.Note that this looks much like a menu program; the form library handles tasks which are in many ways similar, and its interface was obviously designed to resemble that of the menu library wherever possible.
In forms programs, however, the “process user requests” is somewhat more complicated than for menus. Besides menu-like navigation operations, the menu driver loop has to support field editing and data validation.
The basic function for creating fields is
new_field():
FIELD *new_field(int height, int width, /* new field size */
int top, int left, /* upper left corner */
int offscreen, /* number of offscreen rows */
int nbuf); /* number of working buffers */
Menu items always occupy a single row, but forms fields may
have multiple rows. So new_field() requires you to
specify a width and height (the first two arguments, which mist
both be greater than zero).
You must also specify the location of the field's upper left
corner on the screen (the third and fourth arguments, which must
be zero or greater). Note that these coordinates are relative to
the form subwindow, which will coincide with stdscr
by default but need not be stdscr if you have done
an explicit set_form_win() call.
The fifth argument allows you to specify a number of
off-screen rows. If this is zero, the entire field will always be
displayed. If it is nonzero, the form will be scrollable, with
only one screen-full (initially the top part) displayed at any
given time. If you make a field dynamic and grow it so it will no
longer fit on the screen, the form will become scrollable even if
the offscreen argument was initially zero.
The forms library allocates one working buffer per field; the
size of each buffer is ((height + offscreen)*width +
1, one character for each position in the field plus a NUL
terminator. The sixth argument is the number of additional data
buffers to allocate for the field; your application can use them
for its own purposes.
FIELD *dup_field(FIELD *field, /* field to copy */
int top, int left); /* location of new copy */
The function dup_field() duplicates an existing
field at a new location. Size and buffering information are
copied; some attribute flags and status bits are not (see the
form_field_new(3X) for details).
FIELD *link_field(FIELD *field, /* field to copy */
int top, int left); /* location of new copy */
The function link_field() also duplicates an
existing field at a new location. The difference from
dup_field() is that it arranges for the new field's
buffer to be shared with the old one.
Besides the obvious use in making a field editable from two different form pages, linked fields give you a way to hack in dynamic labels. If you declare several fields linked to an original, and then make them inactive, changes from the original will still be propagated to the linked fields.
As with duplicated fields, linked fields have attribute bits separate from the original.
As you might guess, all these field-allocations return
NULL if the field allocation is not possible due to
an out-of-memory error or out-of-bounds arguments.
To connect fields to a form, use
FORM *new_form(FIELD **fields);
This function expects to see a NULL-terminated array of field pointers. Said fields are connected to a newly-allocated form object; its address is returned (or else NULL if the allocation fails).
Note that new_field() does not copy the
pointer array into private storage; if you modify the contents of
the pointer array during forms processing, all manner of bizarre
things might happen. Also note that any given field may only be
connected to one form.
The functions free_field() and
free_form are available to free field and form
objects. It is an error to attempt to free a field connected to a
form, but not vice-versa; thus, you will generally free your form
objects first.
Each form field has a number of location and size attributes
associated with it. There are other field attributes used to
control display and editing of the field. Some (for example, the
O_STATIC bit) involve sufficient complications to be
covered in sections of their own later on. We cover the functions
used to get and set several basic attributes here.
When a field is created, the attributes not specified by the
new_field function are copied from an invisible
system default field. In attribute-setting and -fetching
functions, the argument NULL is taken to mean this field. Changes
to it persist as defaults until your forms application
terminates.
You can retrieve field sizes and locations through:
int field_info(FIELD *field, /* field from which to fetch */
int *height, *int width, /* field size */
int *top, int *left, /* upper left corner */
int *offscreen, /* number of offscreen rows */
int *nbuf); /* number of working buffers */
This function is a sort of inverse of
new_field(); instead of setting size and location
attributes of a new field, it fetches them from an existing
one.
It is possible to move a field's location on the screen:
int move_field(FIELD *field, /* field to alter */
int top, int left); /* new upper-left corner */
You can, of course. query the current location through
field_info().
One-line fields may be unjustified, justified right, justified left, or centered. Here is how you manipulate this attribute:
int set_field_just(FIELD *field, /* field to alter */
int justmode); /* mode to set */
int field_just(FIELD *field); /* fetch mode of field */
The mode values accepted and returned by this functions are
preprocessor macros NO_JUSTIFICATION,
JUSTIFY_RIGHT, JUSTIFY_LEFT, or
JUSTIFY_CENTER.
For each field, you can set a foreground attribute for entered characters, a background attribute for the entire field, and a pad character for the unfilled portion of the field. You can also control pagination of the form.
This group of four field attributes controls the visual appearance of the field on the screen, without affecting in any way the data in the field buffer.
int set_field_fore(FIELD *field, /* field to alter */
chtype attr); /* attribute to set */
chtype field_fore(FIELD *field); /* field to query */
int set_field_back(FIELD *field, /* field to alter */
chtype attr); /* attribute to set */
chtype field_back(FIELD *field); /* field to query */
int set_field_pad(FIELD *field, /* field to alter */
int pad); /* pad character to set */
chtype field_pad(FIELD *field);
int set_new_page(FIELD *field, /* field to alter */
int flag); /* TRUE to force new page */
chtype new_page(FIELD *field); /* field to query */
The attributes set and returned by the first four functions
are normal curses(3x) display attribute values
(A_STANDOUT, A_BOLD,
A_REVERSE etc). The page bit of a field controls
whether it is displayed at the start of a new form screen.
There is also a large collection of field option bits you can set to control various aspects of forms processing. You can manipulate them with these functions:
int set_field_opts(FIELD *field, /* field to alter */
int attr); /* attribute to set */
int field_opts_on(FIELD *field, /* field to alter */
int attr); /* attributes to turn on */
int field_opts_off(FIELD *field, /* field to alter */
int attr); /* attributes to turn off */
int field_opts(FIELD *field); /* field to query */
By default, all options are on. Here are the available option bits:
REQ_PREV_CHOICE and REQ_NEXT_CHOICE
will fail. Such read-only fields may be useful for help
messages.A field's options cannot be changed while the field is currently selected. However, options may be changed on posted fields that are not current.
The option values are bit-masks and can be composed with logical-or in the obvious way.
Every field has a status flag, which is set to FALSE when the field is created and TRUE when the value in field buffer 0 changes. This flag can be queried and set directly:
int set_field_status(FIELD *field, /* field to alter */
int status); /* mode to set */
int field_status(FIELD *field); /* fetch mode of field */
Setting this flag under program control can be useful if you use the same form repeatedly, looking for modified fields each time.
Calling field_status() on a field not currently
selected for input will return a correct value. Calling
field_status() on a field that is currently selected
for input may not necessarily give a correct field status value,
because entered data is not necessarily copied to buffer zero
before the exit validation check. To guarantee that the returned
status value reflects reality, call field_status()
either (1) in the field's exit validation check routine, (2) from
the field's or form's initialization or termination hooks, or (3)
just after a REQ_VALIDATION request has been
processed by the forms driver.
Each field structure contains one character pointer slot that is not used by the forms library. It is intended to be used by applications to store private per-field data. You can manipulate it with:
int set_field_userptr(FIELD *field, /* field to alter */
char *userptr); /* mode to set */
char *field_userptr(FIELD *field); /* fetch mode of field */
(Properly, this user pointer field ought to have (void
*) type. The (char *) type is retained for
System V compatibility.)
It is valid to set the user pointer of the default field (with
a set_field_userptr() call passed a NULL field
pointer.) When a new field is created, the default-field user
pointer is copied to initialize the new field's user pointer.
Normally, a field is fixed at the size specified for it at creation time. If, however, you turn off its O_STATIC bit, it becomes dynamic and will automatically resize itself to accommodate data as it is entered. If the field has extra buffers associated with it, they will grow right along with the main input buffer.
A one-line dynamic field will have a fixed height (1) but variable width, scrolling horizontally to display data within the field area as originally dimensioned and located. A multi-line dynamic field will have a fixed width, but variable height (number of rows), scrolling vertically to display data within the field area as originally dimensioned and located.
Normally, a dynamic field is allowed to grow without limit. But it is possible to set an upper limit on the size of a dynamic field. You do it with this function:
int set_max_field(FIELD *field, /* field to alter (may not be NULL) */
int max_size); /* upper limit on field size */
If the field is one-line, max_size is taken to be
a column size limit; if it is multi-line, it is taken to be a
line size limit. To disable any limit, use an argument of zero.
The growth limit can be changed whether or not the O_STATIC bit
is on, but has no effect until it is.
The following properties of a field change when it becomes dynamic:
O_AUTOSKIP and
O_NL_OVERLOAD are ignored.dup_field() and link_field()
calls copy dynamic-buffer sizes. If the O_STATIC
option is set on one of a collection of links, buffer resizing
will occur only when the field is edited through that
link.field_info() will retrieve the
original static size of the field; use
dynamic_field_info() to get the actual dynamic
size.By default, a field will accept any data that will fit in its input buffer. However, it is possible to attach a validation type to a field. If you do this, any attempt to leave the field while it contains data that does not match the validation type will fail. Some validation types also have a character-validity check for each time a character is entered in the field.
A field's validation check (if any) is not called when
set_field_buffer() modifies the input buffer, nor
when that buffer is changed through a linked field.
The form library provides a rich set of
pre-defined validation types, and gives you the capability to
define custom ones of your own. You can examine and change field
validation attributes with the following functions:
int set_field_type(FIELD *field, /* field to alter */
FIELDTYPE *ftype, /* type to associate */
...); /* additional arguments*/
FIELDTYPE *field_type(FIELD *field); /* field to query */
The validation type of a field is considered an attribute of
the field. As with other field attributes, Also, doing
set_field_type() with a NULL field
default will change the system default for validation of
newly-created fields.
Here are the pre-defined validation types:
This field type accepts alphabetic data; no blanks, no digits, no special characters (this is checked at character-entry time). It is set up with:
int set_field_type(FIELD *field, /* field to alter */
TYPE_ALPHA, /* type to associate */
int width); /* maximum width of field */
The width argument sets a minimum width of data.
Typically you will want to set this to the field width; if it is
greater than the field width, the validation check will always
fail. A minimum width of zero makes field completion
optional.
This field type accepts alphabetic data and digits; no blanks, no special characters (this is checked at character-entry time). It is set up with:
int set_field_type(FIELD *field, /* field to alter */
TYPE_ALNUM, /* type to associate */
int width); /* maximum width of field */
The width argument sets a minimum width of data.
As with TYPE_ALPHA, typically you will want to set this to the
field width; if it is greater than the field width, the
validation check will always fail. A minimum width of zero makes
field completion optional.
This type allows you to restrict a field's values to be among a specified set of string values (for example, the two-letter postal codes for U.S. states). It is set up with:
int set_field_type(FIELD *field, /* field to alter */
TYPE_ENUM, /* type to associate */
char **valuelist; /* list of possible values */
int checkcase; /* case-sensitive? */
int checkunique); /* must specify uniquely? */
The valuelist parameter must point at a
NULL-terminated list of valid strings. The checkcase
argument, if true, makes comparison with the string
case-sensitive.
When the user exits a TYPE_ENUM field, the validation procedure tries to complete the data in the buffer to a valid entry. If a complete choice string has been entered, it is of course valid. But it is also possible to enter a prefix of a valid string and have it completed for you.
By default, if you enter such a prefix and it matches more
than one value in the string list, the prefix will be completed
to the first matching value. But the checkunique
argument, if true, requires prefix matches to be unique in order
to be valid.
The REQ_NEXT_CHOICE and
REQ_PREV_CHOICE input requests can be particularly
useful with these fields.
This field type accepts an integer. It is set up as follows:
int set_field_type(FIELD *field, /* field to alter */
TYPE_INTEGER, /* type to associate */
int padding, /* # places to zero-pad to */
int vmin, int vmax); /* valid range */
Valid characters consist of an optional leading minus and digits. The range check is performed on exit. If the range maximum is less than or equal to the minimum, the range is ignored.
If the value passes its range check, it is padded with as many leading zero digits as necessary to meet the padding argument.
A TYPE_INTEGER value buffer can conveniently be
interpreted with the C library function atoi(3).
This field type accepts a decimal number. It is set up as follows:
int set_field_type(FIELD *field, /* field to alter */
TYPE_NUMERIC, /* type to associate */
int padding, /* # places of precision */
double vmin, double vmax); /* valid range */
Valid characters consist of an optional leading minus and digits. possibly including a decimal point. If your system supports locale's, the decimal point character used must be the one defined by your locale. The range check is performed on exit. If the range maximum is less than or equal to the minimum, the range is ignored.
If the value passes its range check, it is padded with as many trailing zero digits as necessary to meet the padding argument.
A TYPE_NUMERIC value buffer can conveniently be
interpreted with the C library function atof(3).
This field type accepts data matching a regular expression. It is set up as follows:
int set_field_type(FIELD *field, /* field to alter */
TYPE_REGEXP, /* type to associate */
char *regexp); /* expression to match */
The syntax for regular expressions is that of
regcomp(3). The check for regular-expression match
is performed on exit.
The chief attribute of a field is its buffer contents. When a form has been completed, your application usually needs to know the state of each field buffer. You can find this out with:
char *field_buffer(FIELD *field, /* field to query */
int bufindex); /* number of buffer to query */
Normally, the state of the zero-numbered buffer for each field is set by the user's editing actions on that field. It is sometimes useful to be able to set the value of the zero-numbered (or some other) buffer from your application:
int set_field_buffer(FIELD *field, /* field to alter */
int bufindex, /* number of buffer to alter */
char *value); /* string value to set */
If the field is not large enough and cannot be resized to a sufficiently large size to contain the specified value, the value will be truncated to fit.
Calling field_buffer() with a null field pointer
will raise an error. Calling field_buffer() on a
field not currently selected for input will return a correct
value. Calling field_buffer() on a field that is
currently selected for input may not necessarily give a correct
field buffer value, because entered data is not necessarily
copied to buffer zero before the exit validation check. To
guarantee that the returned buffer value reflects on-screen
reality, call field_buffer() either (1) in the
field's exit validation check routine, (2) from the field's or
form's initialization or termination hooks, or (3) just after a
REQ_VALIDATION request has been processed by the
forms driver.
As with field attributes, form attributes inherit a default
from a system default form structure. These defaults can be
queried or set by of these functions using a form-pointer
argument of NULL.
The principal attribute of a form is its field list. You can query and change this list with:
int set_form_fields(FORM *form, /* form to alter */
FIELD **fields); /* fields to connect */
char *form_fields(FORM *form); /* fetch fields of form */
int field_count(FORM *form); /* count connect fields */
The second argument of set_form_fields() may be a
NULL-terminated field pointer array like the one required by
new_form(). In that case, the old fields of the form
are disconnected but not freed (and eligible to be connected to
other forms), then the new fields are connected.
It may also be null, in which case the old fields are disconnected (and not freed) but no new ones are connected.
The field_count() function simply counts the
number of fields connected to a given from. It returns -1 if the
form-pointer argument is NULL.
In the overview section, you saw that to display a form you
normally start by defining its size (and fields), posting it, and
refreshing the screen. There is an hidden step before posting,
which is the association of the form with a frame window
(actually, a pair of windows) within which it will be displayed.
By default, the forms library associates every form with the
full-screen window stdscr.
By making this step explicit, you can associate a form with a declared frame window on your screen display. This can be useful if you want to adapt the form display to different screen sizes, dynamically tile forms on the screen, or use a form as part of an interface layout managed by panels.
The two windows associated with each form have the same functions as their analogues in the menu library. Both these windows are painted when the form is posted and erased when the form is unposted.
The outer or frame window is not otherwise touched by the form routines. It exists so the programmer can associate a title, a border, or perhaps help text with the form and have it properly refreshed or erased at post/unpost time. The inner window or subwindow is where the current form page is actually displayed.
In order to declare your own frame window for a form, you will need to know the size of the form's bounding rectangle. You can get this information with:
int scale_form(FORM *form, /* form to query */
int *rows, /* form rows */
int *cols); /* form cols */
The form dimensions are passed back in the locations pointed to by the arguments. Once you have this information, you can use it to declare of windows, then use one of these functions:
int set_form_win(FORM *form, /* form to alter */
WINDOW *win); /* frame window to connect */
WINDOW *form_win(FORM *form); /* fetch frame window of form */
int set_form_sub(FORM *form, /* form to alter */
WINDOW *win); /* form subwindow to connect */
WINDOW *form_sub(FORM *form); /* fetch form subwindow of form */
Note that curses operations, including refresh(),
on the form, should be done on the frame window, not the form
subwindow.
It is possible to check from your application whether all of a scrollable field is actually displayed within the menu subwindow. Use these functions:
int data_ahead(FORM *form); /* form to be queried */ int data_behind(FORM *form); /* form to be queried */
The function data_ahead() returns TRUE if (a) the
current field is one-line and has undisplayed data off to the
right, (b) the current field is multi-line and there is data
off-screen below it.
The function data_behind() returns TRUE if the
first (upper left hand) character position is off-screen (not
being displayed).
Finally, there is a function to restore the form window's cursor to the value expected by the forms driver:
int pos_form_cursor(FORM *) /* form to be queried */
If your application changes the form window cursor, call this function before handing control back to the forms driver in order to re-synchronize it.
The function form_driver() handles virtualized
input requests for form navigation, editing, and validation
requests, just as menu_driver does for menus (see
the section on menu input handling).
int form_driver(FORM *form, /* form to pass input to */
int request); /* form request code */
Your input virtualization function needs to take input and then convert it to either an alphanumeric character (which is treated as data to be entered in the currently-selected field), or a forms processing request.
The forms driver provides hooks (through input-validation and field-termination functions) with which your application code can check that the input taken by the driver matched what was expected.
These requests cause page-level moves through the form, triggering display of a new form screen.
REQ_NEXT_PAGE
REQ_PREV_PAGE
REQ_FIRST_PAGE
REQ_LAST_PAGE
These requests treat the list as cyclic; that is,
REQ_NEXT_PAGE from the last page goes to the first,
and REQ_PREV_PAGE from the first page goes to the
last.
These requests handle navigation between fields on the same page.
REQ_NEXT_FIELD
REQ_PREV_FIELD
REQ_FIRST_FIELD
REQ_LAST_FIELD
REQ_SNEXT_FIELD
REQ_SPREV_FIELD
REQ_SFIRST_FIELD
REQ_SLAST_FIELD
REQ_LEFT_FIELD
REQ_RIGHT_FIELD
REQ_UP_FIELD
REQ_DOWN_FIELD
These requests treat the list of fields on a page as cyclic;
that is, REQ_NEXT_FIELD from the last field goes to
the first, and REQ_PREV_FIELD from the first field
goes to the last. The order of the fields for these (and the
REQ_FIRST_FIELD and REQ_LAST_FIELD
requests) is simply the order of the field pointers in the form
array (as set up by new_form() or
set_form_fields()
It is also possible to traverse the fields as if they had been sorted in screen-position order, so the sequence goes left-to-right and top-to-bottom. To do this, use the second group of four sorted-movement requests.
Finally, it is possible to move between fields using visual directions up, down, right, and left. To accomplish this, use the third group of four requests. Note, however, that the position of a form for purposes of these requests is its upper-left corner.
For example, suppose you have a multi-line field B, and two
single-line fields A and C on the same line with B, with A to the
left of B and C to the right of B. A REQ_MOVE_RIGHT
from A will go to B only if A, B, and C all share the
same first line; otherwise it will skip over B to C.
These requests drive movement of the edit cursor within the currently selected field.
REQ_NEXT_CHAR
REQ_PREV_CHAR
REQ_NEXT_LINE
REQ_PREV_LINE
REQ_NEXT_WORD
REQ_PREV_WORD
REQ_BEG_FIELD
REQ_END_FIELD
REQ_BEG_LINE
REQ_END_LINE
REQ_LEFT_CHAR
REQ_RIGHT_CHAR
REQ_UP_CHAR
REQ_DOWN_CHAR
Each word is separated from the previous and next characters by whitespace. The commands to move to beginning and end of line or field look for the first or last non-pad character in their ranges.
Fields that are dynamic and have grown and fields explicitly created with offscreen rows are scrollable. One-line fields scroll horizontally; multi-line fields scroll vertically. Most scrolling is triggered by editing and intra-field movement (the library scrolls the field to keep the cursor visible). It is possible to explicitly request scrolling with the following requests:
REQ_SCR_FLINE
REQ_SCR_BLINE
REQ_SCR_FPAGE
REQ_SCR_BPAGE
REQ_SCR_FHPAGE
REQ_SCR_BHPAGE
REQ_SCR_FCHAR
REQ_SCR_BCHAR
REQ_SCR_HFLINE
REQ_SCR_HBLINE
REQ_SCR_HFHALF
REQ_SCR_HBHALF
For scrolling purposes, a page of a field is the height of its visible part.
When you pass the forms driver an ASCII character, it is treated as a request to add the character to the field's data buffer. Whether this is an insertion or a replacement depends on the field's edit mode (insertion is the default.
The following requests support editing the field and changing the edit mode:
REQ_INS_MODE
REQ_OVL_MODE
REQ_NEW_LINE
REQ_INS_CHAR
REQ_INS_LINE
REQ_DEL_CHAR
REQ_DEL_PREV
REQ_DEL_LINE
REQ_DEL_WORD
REQ_CLR_EOL
REQ_CLR_EOF
REQ_CLEAR_FIELD
The behavior of the REQ_NEW_LINE and
REQ_DEL_PREV requests is complicated and partly
controlled by a pair of forms options. The special cases are
triggered when the cursor is at the beginning of a field, or on
the last line of the field.
First, we consider REQ_NEW_LINE:
The normal behavior of REQ_NEW_LINE in insert
mode is to break the current line at the position of the edit
cursor, inserting the portion of the current line after the
cursor as a new line following the current and moving the cursor
to the beginning of that new line (you may think of this as
inserting a newline in the field buffer).
The normal behavior of REQ_NEW_LINE in overlay
mode is to clear the current line from the position of the edit
cursor to end of line. The cursor is then moved to the beginning
of the next line.
However, REQ_NEW_LINE at the beginning of a
field, or on the last line of a field, instead does a
REQ_NEXT_FIELD. O_NL_OVERLOAD option is
off, this special action is disabled.
Now, let us consider REQ_DEL_PREV:
The normal behavior of REQ_DEL_PREV is to delete
the previous character. If insert mode is on, and the cursor is
at the start of a line, and the text on that line will fit on the
previous one, it instead appends the contents of the current line
to the previous one and deletes the current line (you may think
of this as deleting a newline from the field buffer).
However, REQ_DEL_PREV at the beginning of a field
is instead treated as a REQ_PREV_FIELD.
If the O_BS_OVERLOAD option is off, this special
action is disabled and the forms driver just returns
E_REQUEST_DENIED.
See Form Options for discussion of how to set and clear the overload options.
If the type of your field is ordered, and has associated functions for getting the next and previous values of the type from a given value, there are requests that can fetch that value into the field buffer:
REQ_NEXT_CHOICE
REQ_PREV_CHOICE
Of the built-in field types, only TYPE_ENUM has
built-in successor and predecessor functions. When you define a
field type of your own (see Custom Validation
Types), you can associate our own ordering functions.
Form requests are represented as integers above the
curses value greater than KEY_MAX and
less than or equal to the constant MAX_COMMAND. If
your input-virtualization routine returns a value above
MAX_COMMAND, the forms driver will ignore it.
It is possible to set function hooks to be executed whenever the current field or form changes. Here are the functions that support this:
typedef void (*HOOK)(); /* pointer to function returning void */
int set_form_init(FORM *form, /* form to alter */
HOOK hook); /* initialization hook */
HOOK form_init(FORM *form); /* form to query */
int set_form_term(FORM *form, /* form to alter */
HOOK hook); /* termination hook */
HOOK form_term(FORM *form); /* form to query */
int set_field_init(FORM *form, /* form to alter */
HOOK hook); /* initialization hook */
HOOK field_init(FORM *form); /* form to query */
int set_field_term(FORM *form, /* form to alter */
HOOK hook); /* termination hook */
HOOK field_term(FORM *form); /* form to query */
These functions allow you to either set or query four different hooks. In each of the set functions, the second argument should be the address of a hook function. These functions differ only in the timing of the hook call.
Calls to these hooks may be triggered
set_current_field() callset_form_page() callSee Field Change Commands for discussion of the latter two cases.
You can set a default hook for all fields by passing one of the set functions a NULL first argument.
You can disable any of these hooks by (re)setting them to NULL, the default value.
Normally, navigation through the form will be driven by the user's input requests. But sometimes it is useful to be able to move the focus for editing and viewing under control of your application, or ask which field it currently is in. The following functions help you accomplish this:
int set_current_field(FORM *form, /* form to alter */
FIELD *field); /* field to shift to */
FIELD *current_field(FORM *form); /* form to query */
int field_index(FORM *form, /* form to query */
FIELD *field); /* field to get index of */
The function field_index() returns the index of
the given field in the given form's field array (the array passed
to new_form() or
set_form_fields()).
The initial current field of a form is the first active field
on the first page. The function set_form_fields()
resets this.
It is also possible to move around by pages.
int set_form_page(FORM *form, /* form to alter */
int page); /* page to go to (0-origin) */
int form_page(FORM *form); /* return form's current page */
The initial page of a newly-created form is 0. The function
set_form_fields() resets this.
Like fields, forms may have control option bits. They can be changed or queried with these functions:
int set_form_opts(FORM *form, /* form to alter */
int attr); /* attribute to set */
int form_opts_on(FORM *form, /* form to alter */
int attr); /* attributes to turn on */
int form_opts_off(FORM *form, /* form to alter */
int attr); /* attributes to turn off */
int form_opts(FORM *form); /* form to query */
By default, all options are on. Here are the available option bits:
REQ_NEW_LINE as
described in Editing Requests. The value
of this option is ignored on dynamic fields that have not
reached their size limit; these have no last line, so the
circumstances for triggering a REQ_NEXT_FIELD
never arise.REQ_DEL_PREV as
described in Editing Requests.The option values are bit-masks and can be composed with logical-or in the obvious way.
The form library gives you the capability to
define custom validation types of your own. Further, the optional
additional arguments of set_field_type effectively
allow you to parameterize validation types. Most of the
complications in the validation-type interface have to do with
the handling of the additional arguments within custom validation
functions.
The simplest way to create a custom data type is to compose it from two preexisting ones:
FIELD *link_fieldtype(FIELDTYPE *type1,
FIELDTYPE *type2);
This function creates a field type that will accept any of the
values legal for either of its argument field types (which may be
either predefined or programmer-defined). If a
set_field_type() call later requires arguments, the
new composite type expects all arguments for the first type, than
all arguments for the second. Order functions (see Order Requests) associated with the component types
will work on the composite; what it does is check the validation
function for the first type, then for the second, to figure what
type the buffer contents should be treated as.
To create a field type from scratch, you need to specify one or both of the following things:
Here is how you do that:
typedef int (*HOOK)(); /* pointer to function returning int */
FIELDTYPE *new_fieldtype(HOOK f_validate, /* field validator */
HOOK c_validate) /* character validator */
int free_fieldtype(FIELDTYPE *ftype); /* type to free */
At least one of the arguments of new_fieldtype()
must be non-NULL. The forms driver will automatically call the
new type's validation functions at appropriate points in
processing a field of the new type.
The function free_fieldtype() deallocates the
argument fieldtype, freeing all storage associated with it.
Normally, a field validator is called when the user attempts to leave the field. Its first argument is a field pointer, from which it can get to field buffer 0 and test it. If the function returns TRUE, the operation succeeds; if it returns FALSE, the edit cursor stays in the field.
A character validator gets the character passed in as a first argument. It too should return TRUE if the character is valid, FALSE otherwise.
Your field- and character- validation functions will be passed
a second argument as well. This second argument is the address of
a structure (which we will call a pile) built from any
of the field-type-specific arguments passed to
set_field_type(). If no such arguments are defined
for the field type, this pile pointer argument will be NULL.
In order to arrange for such arguments to be passed to your
validation functions, you must associate a small set of
storage-management functions with the type. The forms driver will
use these to synthesize a pile from the trailing arguments of
each set_field_type() argument, and a pointer to the
pile will be passed to the validation functions.
Here is how you make the association:
typedef char *(*PTRHOOK)(); /* pointer to function returning (char *) */
typedef void (*VOIDHOOK)(); /* pointer to function returning void */
int set_fieldtype_arg(FIELDTYPE *type, /* type to alter */
PTRHOOK make_str, /* make structure from args */
PTRHOOK copy_str, /* make copy of structure */
VOIDHOOK free_str); /* free structure storage */
Here is how the storage-management hooks are used:
make_str
set_field_type().
It gets one argument, a va_list of the
type-specific arguments passed to
set_field_type(). It is expected to return a pile
pointer to a data structure that encapsulates those
arguments.copy_str
free_str
The make_str and copy_str functions
may return NULL to signal allocation failure. The library
routines will that call them will return error indication when
this happens. Thus, your validation functions should never see a
NULL file pointer and need not check specially for it.
Some custom field types are simply ordered in the same
well-defined way that TYPE_ENUM is. For such types,
it is possible to define successor and predecessor functions to
support the REQ_NEXT_CHOICE and
REQ_PREV_CHOICE requests. Here is how:
typedef int (*INTHOOK)(); /* pointer to function returning int */
int set_fieldtype_arg(FIELDTYPE *type, /* type to alter */
INTHOOK succ, /* get successor value */
INTHOOK pred); /* get predecessor value */
The successor and predecessor arguments will each be passed
two arguments; a field pointer, and a pile pointer (as for the
validation functions). They are expected to use the function
field_buffer() to read the current value, and
set_field_buffer() on buffer 0 to set the next or
previous value. Either hook may return TRUE to indicate success
(a legal next or previous value was set) or FALSE to indicate
failure.
The interface for defining custom types is complicated and tricky. Rather than attempting to create a custom type entirely from scratch, you should start by studying the library source code for whichever of the pre-defined types seems to be closest to what you want.
Use that code as a model, and evolve it towards what you
really want. You will avoid many problems and annoyances that
way. The code in the ncurses library has been
specifically exempted from the package copyright to support
this.
If your custom type defines order functions, have do something intuitive with a blank field. A useful convention is to make the successor of a blank field the types minimum value, and its predecessor the maximum.