-
Writing Programs with NCURSES
by Eric S. Raymond and Zeyd M. Ben-Halim
A Brief History of Curses
Historically, the first ancestor of curses was the routines written to
- provide screen-handling for the game rogue; these used the
- already-existing termcap database facility for describing terminal
+ 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.
-
- 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.
+ 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.
Scope of This Document
curses API with some clearly marked extensions. It includes the
following System V curses features:
* Support for multiple screen highlights (BSD curses could only
- handle one `standout' highlight, usually reverse-video).
+ handle one "standout" highlight, usually reverse-video).
* Support for line- and box-drawing using forms characters.
* Recognition of function keys on input.
* Color support.
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
+ 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
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
+ in versions after 1.8.1 and wrote most of this introduction. Juergen
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.
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 doesn't bear
- any necessary relation to what is really on the terminal screen; it's
+ 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
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
+ 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
+ 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.
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
+ prefix "mv" and the desired (y, x) coordinates prepended to the
arguments to the function. For example, the calls
move(y, x);
addch(ch);
general usefulness:
bool
- boolean type, actually a `char' (e.g., bool doneit;)
+ boolean type, actually a "char" (e.g., bool doneit;)
TRUE
- boolean `true' flag (1).
+ boolean "true" flag (1).
FALSE
- boolean `false' flag (0).
+ boolean "false" flag (0).
ERR
error flag returned by routines on a failure (-1).
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>
/* process the command keystroke */
}
- finish(0); /* we're done */
+ finish(0); /* we are done */
}
static void finish(int sig)
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
+ 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(),
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
+ 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
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
+ 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
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
+ 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.
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.
+ 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
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
+ 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.
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(), ripofflines(), use_env(),
+ before initscr (slk_init(), filter(), ripoffline(), use_env(),
and, if you are using multiple terminals, newterm().)
endwin()
the terminal, as other routines merely manipulate data
structures. 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.
+ 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)
These two functions allow multiple updates with more efficiency
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.
+ this array, so you will have to save it yourself if need be.
Debugging
trace()
This function can be used to explicitly set a trace level. If
the trace level is nonzero, execution of your program will
- generate a file called `trace' in the current working directory
+ generate a file called "trace" in the current working directory
containing a report on the library's actions. Higher trace
levels enable more detailed (and verbose) reporting -- see
comments attached to TRACE_ defines in the curses.h file for
Some Notes of Caution
If you find yourself thinking you need to use noraw() or nocbreak(),
- think again and move carefully. It's probably better design to use
+ 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
likely to hurt your application's usability with other curses
libraries.
- Bear in mind that refresh() is a synonym for wrefresh(stdscr). Don't
+ 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
Temporarily Leaving NCURSES Mode
Sometimes you will want to write a program that spends most of its
- time in screen mode, but occasionally returns to ordinary `cooked'
+ 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.
Using NCURSES under XTERM
A resize operation in X sends SIGWINCH to the application running
- under xterm. The ncurses library provides an experimental signal
- handler, but in general does not catch this signal, because it cannot
- know how you want the screen re-painted. You will usually have to
- write the SIGWINCH handler yourself. Ncurses can give you some help.
-
- The easiest way to code your SIGWINCH handler is to have it 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.
+ 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
limited to the new screen dimensions, and pads stdscr with blanks if
the screen is larger.
- Finally, ncurses can be configured to provide its own SIGWINCH
- handler, based on resizeterm.
+ 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.
Handling Multiple Terminal Screens
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
+ 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.
Tuning for Speed
Use the addchstr() family of functions for fast screen-painting of
- text when you know the text doesn't contain any control characters.
- Try to make attribute changes infrequent on your screens. Don't use
+ 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!
Special Features of NCURSES
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.
+ 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
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
+ 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
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
+ 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.
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.
+ 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
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.
+ 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 isn't sufficient because it doesn't update the
+ 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.
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'll generate a lot of unnecessary refresh activity and
+ write, you will generate a lot of unnecessary refresh activity and
screen flicker.
Panels, Input, and the Standard Screen
- You shouldn't mix wnoutrefresh() or wrefresh() operations with panels
+ 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.
Hiding Panels
- It's possible to remove a panel from the deck temporarily; use
+ 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.
Miscellaneous Other Facilities
- It's possible to navigate the deck using the functions panel_above()
+ 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.
1. Initialize curses.
2. Create the menu items, using new_item().
3. Create the menu using new_menu().
- 4. Post the menu using menu_post().
+ 4. Post the menu using post_menu().
5. Refresh the screen.
6. Process user requests via an input loop.
- 7. Unpost the menu using menu_unpost().
+ 7. Unpost the menu using unpost_menu().
8. Free the menu, using free_menu().
9. Free the items using free_item().
10. Terminate curses.
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'
+ (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
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
+ 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.
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
+ 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
1. Initialize curses.
2. Create the form fields, using new_field().
3. Create the form using new_form().
- 4. Post the form using form_post().
+ 4. Post the form using post_form().
5. Refresh the screen.
6. Process user requests via an input loop.
- 7. Unpost the form using form_unpost().
+ 7. Unpost the form using unpost_form().
8. Free the form, using free_form().
9. Free the fields using free_field().
10. Terminate curses.
obviously designed to resemble that of the menu library wherever
possible.
- In forms programs, however, the `process user requests' is somewhat
+ 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 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.
+ 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
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
+ 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
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 doesn't match the validation type will fail. Some
+ 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.
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.
+ 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.
TYPE_ALNUM
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.
+ 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.
TYPE_ENUM
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
+ 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 */
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
+ 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
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
+ 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 */
O_NL_OVERLOAD
Enable overloading of 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
+ 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.
O_BS_OVERLOAD
entered.
* A field-validation function to be applied on exit from the field.
- Here's how you do that:
+ 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
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'll call a pile) built from any of the
+ 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.
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's how:
+ REQ_PREV_CHOICE requests. Here is how:
typedef int (*INTHOOK)(); /* pointer to function returning int */
int set_fieldtype_arg(FIELDTYPE *type, /* type to alter */
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