by Eric S. Raymond and Zeyd M. Ben-Halim
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 screenfull 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.
System III UNIX from Bell Labs featured a rewritten and much-improved curses library. It introduced the terminfo format. 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.
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 primary maintainer of the 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.
This document also describes the 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. This code was contributed to the project by Jürgen Pfeifer.
#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.
A window is a purely internal representation. It is used to build and store a potential image of a portion of the terminal. It doesn't bear any necessary relation to what is really on the terminal screen; it's 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.
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 `w'indow-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.
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:
Here is a sample program to motivate the discussion:
#include <curses.h>
#include <signal.h>
static void finish(int sig);
main(int argc, char *argv[])
{
/* 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) noecho(); /* don't echo input */
if (has_colors())
{
start_color();
/*
* Simple color assignment, often all we need.
*/
init_pair(COLOR_BLACK, COLOR_BLACK, COLOR_BLACK);
init_pair(COLOR_GREEN, COLOR_GREEN, COLOR_BLACK);
init_pair(COLOR_RED, COLOR_RED, COLOR_BLACK);
init_pair(COLOR_CYAN, COLOR_CYAN, COLOR_BLACK);
init_pair(COLOR_WHITE, COLOR_WHITE, COLOR_BLACK);
init_pair(COLOR_MAGENTA, COLOR_MAGENTA, COLOR_BLACK);
init_pair(COLOR_BLUE, COLOR_BLUE, COLOR_BLACK);
init_pair(COLOR_YELLOW, COLOR_YELLOW, COLOR_BLACK);
}
for (;;)
{
int c = getch(); /* refresh, accept single keystroke of input */
/* process the command keystroke */
}
finish(0); /* we're done */
}
static void finish(int sig)
{
endwin();
/* do your non-curses wrapup here */
exit(0);
}
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 isn't 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.
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.
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 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.
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-or'ed 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've 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.
Presently, mouse event reporting works only under xterm. In the future, ncurses will detect the presence of \fBgpm\fR(1), Alessandro Rubini's freeware mouse server for Linux systems, and accept mouse reports through it.
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'll 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 touchscreens 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 don't 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.
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'll have to save it yourself if need be.
Bear in mind that refresh() is a synonym for wrefresh(stdscr), and don't 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 freeware 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.
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 */
The easiest way to code your SIGWINCH handler is to have it do an endwin, followed by an initscr and a screen repaint you code yourself. The initscr will pick up the new screen size from the xterm's environment.
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.
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.
The wresize() function allows you to resize a window in place.
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 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's 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 wnoutrfresh() 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.
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.
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.
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 freeware panel code distributed
with ncurses.
#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. Most modern linkers
are two-pass and will accept either order, but it is still good practice
to put -lpanel first and -lncurses second.
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'll 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 doesn't
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 isn't sufficient because it
doesn't 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, youll generate a lot of unnecessary refresh
activity and screen flicker.
wnoutrefresh() or wrefresh()
operations with panels code; this will work only if the argument window
is either in the top panel or un-obscured 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 un-obscured.
There is presently no way to display changes to one obscured panel without repainting all panels.
hide_panel for this. You can un-hide a panel with
show_panel(). 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.
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.
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 freeware menu code distributed
with ncurses.
#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. Most modern linkers
are two-pass and will accept either order, but it is still good practice
to put -lmenu first and -lncurses second.
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().
menu_post().
menu_unpost().
free_menu().
free_item().
curses.
mitem_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 un-selectable 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.
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.
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 menu_post(), you write the menu to its
subwindow. When you call menu_unpost(), you erase the
subwindow, However, neither of these actually modifies the screen. To
do that, call wrefresh() or some equivalent.
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'll 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.
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).
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 freeware form code distributed
with ncurses.
#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. Most modern linkers
are two-pass and will accept either order, but it is still good practice
to put -lform first and -lncurses second.
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().
form_post().
form_unpost().
free_form().
free_field().
curses.
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.
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've done an explicit set_form_window() 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 \fBoffscreen\fR 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.
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.
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.
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().
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.
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.
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:
The option values are bit-masks and can be composed with logical-or in the obvious way.
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 isn't 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.
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.
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:
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:
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'll want to set this to the field width; if it's greater than the
field width, the validation check will always fail. A minimum width
of zero makes field completion optional.
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'll want to set this to the field width; if it's
greater than the field width, the validation check will always fail. A
minimum width of zero makes field completion optional.
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.
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).
int set_field_type(FIELD *field, /* field to alter */
TYPE_NUMERIC, /* type to associate */
int padding, /* # places of precision */
int vmin, int vmax); /* valid range */
Valid characters consist of an optional leading minus and digits. possibly
including a decimal point. 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).
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.
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's 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 isn't 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.
The most important 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.
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'll 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.
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.
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.
The following requests support editing the field and changing the edit mode:
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.
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.
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.
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.
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:
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.
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 fointer, 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.
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:
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.
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 un-copyrighted 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.
THIS DOCUMENT IS STILL UNDER CONSTRUCTION. Full descriptions of the form library entry points are available in the form_*.3x manual pages included with the ncurses distributions.