Writing Programs with NCURSES
+Writing Programs with NCURSES
+
by Eric S. Raymond and Zeyd M. Ben-Halim
updates since release 1.9.9e by Thomas Dickey
- Contents
+Contents
* Introduction
+ A Brief History of Curses
o Avoiding Problems
_________________________________________________________________
- Introduction
+Introduction
This document is an introduction to programming with curses. It is not
an exhaustive reference for the curses Application Programming
will typically be a great deal simpler and less expensive than one
using an X toolkit.
-A Brief History of Curses
+ A Brief History of Curses
Historically, the first ancestor of curses was the routines written to
provide screen-handling for the vi editor; these used the termcap
releases, curses evolved to use more facilities and offer more
capabilities, going far beyond BSD curses in power and flexibility.
-Scope of This Document
+ Scope of This Document
This document describes ncurses, a free implementation of the System V
curses API with some clearly marked extensions. It includes the
extension libraries, also cloned from System V, which support easy
construction and sequences of menus and fill-in forms.
-Terminology
+ Terminology
In this document, the following terminology is used with reasonable
consistency:
The package's idea of what the terminal display currently looks
like, i.e., what the user sees now. This is a special screen.
- The Curses Library
+The Curses Library
-An Overview of Curses
+ An Overview of Curses
- Compiling Programs using Curses
+ Compiling Programs using Curses
In order to use the library, it is necessary to have certain types and
variables defined. Therefore, the programmer must have a line:
your LDFLAGS or on the command line. There is no need for any other
libraries.
- Updating the Screen
+ Updating the Screen
In order to update the screen optimally, it is necessary for the
routines to know what the screen currently looks like and what the
package implementation determine the most efficient way to repaint the
screen.
- Standard Windows and Function Naming Conventions
+ Standard Windows and Function Naming Conventions
As hinted above, the routines can use several windows, but two are
automatically given: curscr, which knows what the terminal looks like,
(y, x) coordinates. If a function requires a window pointer, it is
always the first parameter passed.
- Variables
+ Variables
The curses library sets some variables describing the terminal
capabilities.
OK
error flag returned by routines when things go right.
-Using the Library
+ Using the Library
Now we describe how to actually use the screen package. In it, we
assume all updating, reading, etc. is applied to stdscr. These
exit(0);
}
- Starting up
+ Starting up
In order to use the screen package, the routines must know about
terminal characteristics, and the space for curscr and stdscr must be
of old windows. All the options described above can be applied to any
window.
- Output
+ Output
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
implementing a command which would redraw the screen in case it get
messed up.
- Input
+ Input
The complementary function to addch() is getch() which, if echo is
set, will call addch() to echo the character. Since the screen package
curses.h The mapping from sequences to #define values is determined by
key_ capabilities in the terminal's terminfo entry.
- Using Forms Characters
+ Using Forms Characters
The addch() function (and some others, including box() and border())
can accept some pseudo-character arguments which are specially defined
the terminal does not have such characters, curses.h will map them to
a recognizable (though ugly) set of ASCII defaults.
- Character Attributes and Color
+ Character Attributes and Color
The ncurses package supports screen highlights including standout,
reverse-video, underline, and blink. It also supports color, which is
combination. Note that COLOR_PAIR(N), for constant N, is itself a
compile-time constant and can be used in initializers.
- Mouse Interfacing
+ Mouse Interfacing
The ncurses library also provides a mouse interface.
See the manual page curs_mouse(3X) for full details of the
mouse-interface functions.
- Finishing Up
+ Finishing Up
In order to clean up after the ncurses routines, the routine endwin()
is provided. It restores tty modes to what they were when initscr()
Thus, anytime after the call to initscr, endwin() should be called
before exiting.
-Function Descriptions
+ Function Descriptions
We describe the detailed behavior of some important curses functions
here, as a supplement to the manual page descriptions.
- Initialization and Wrapup
+ Initialization and Wrapup
initscr()
The first function called should almost always be initscr().
The inverse of newterm(); deallocates the data structures
associated with a given SCREEN reference.
- Causing Output to the Terminal
+ Causing Output to the Terminal
refresh() and wrefresh(win)
These functions must be called to actually get any output on
with fewer total characters transmitted (this also avoids a
visually annoying flicker at each update).
- Low-Level Capability Access
+ Low-Level Capability Access
setupterm(term, filenum, errret)
This routine is called to initialize a terminal's description,
array ttytype[]. Subsequent calls to setupterm() will overwrite
this array, so you will have to save it yourself if need be.
- Debugging
+ Debugging
NOTE: These functions are not part of the standard curses API!
single-line pseudo-operations. These pseudo-ops can be distinguished
by the fact that they are named in capital letters.
-Hints, Tips, and Tricks
+ Hints, Tips, and Tricks
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.
- Some Notes of Caution
+ Some Notes of Caution
If you find yourself thinking you need to use noraw() or nocbreak(),
think again and move carefully. It is probably better design to use
in an environment with window resizes, in which case several screens
could be open with different sizes.
- Temporarily Leaving NCURSES Mode
+ 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"
addstr("returned.\n"); /* prepare return message */
refresh(); /* restore save modes, repaint screen */
- Using NCURSES under XTERM
+ Using NCURSES under XTERM
A resize operation in X sends SIGWINCH to the application running
under xterm. The easiest way to handle SIGWINCH is to do an endwin,
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
+ Handling Multiple Terminal Screens
The initscr() function actually calls a function named newterm() to do
most of its work. If you are writing a program that opens multiple
with the set_term call. Note that you will also have to call
def_shell_mode and def_prog_mode on each tty yourself.
- Testing for Terminal Capabilities
+ Testing for Terminal Capabilities
Sometimes you may want to write programs that test for the presence of
various capabilities before deciding whether to go into ncurses mode.
can include the term.h file and test the value of the macro
cursor_address.
- Tuning for Speed
+ Tuning for Speed
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!
- Special Features of NCURSES
+ Special Features of NCURSES
The wresize() function allows you to resize a window in place. The
associated resizeterm() function simplifies the construction of
8. While most terminals which provide color allow only 8 colors, about
a quarter (including XFree86 xterm) support 16 colors.
-Compatibility with Older Versions
+ Compatibility with Older Versions
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.
- Refresh of Overlapping Windows
+ Refresh of Overlapping Windows
If you define two windows A and B that overlap, and then alternately
scribble on and refresh them, the changes made to the overlapping
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.
- Background Erase
+ Background Erase
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
This change in behavior conforms ncurses to System V Release 4 and the
XSI Curses standard.
-XSI Curses Conformance
+ XSI Curses Conformance
The ncurses library is intended to be base-level conformant with the
XSI Curses standard from X/Open. Many extended-level features (in
have a corresponding function which may be linked (and will be
prototype-checked) if the macro definition is disabled with #undef.
- The Panels Library
+The Panels Library
The ncurses library by itself provides good support for screen
displays in which the windows are tiled (non-overlapping). In the more
The panel library first appeared in AT&T System V. The version
documented here is the panel code distributed with ncurses.
-Compiling With the Panels Library
+ Compiling With the Panels Library
Your panels-using modules must import the panels library declarations
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.
-Overview of Panels
+ Overview of Panels
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
write, you will generate a lot of unnecessary refresh activity and
screen flicker.
-Panels, Input, and the Standard Screen
+ Panels, Input, and the Standard Screen
You should not mix wnoutrefresh() or wrefresh() operations with panels
code; this will work only if the argument window is either in the top
There is presently no way to display changes to one obscured panel
without repainting all panels.
-Hiding Panels
+ Hiding 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
or bottom_panel on a hidden panel(). Other panels operations are
applicable.
-Miscellaneous Other Facilities
+ Miscellaneous Other Facilities
It is possible to navigate the deck using the functions panel_above()
and panel_below. Handed a panel pointer, they return the panel above
code, to which you can attach application data. See the man page
documentation of set_panel_userptr() and panel_userptr for details.
- The Menu Library
+The Menu Library
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
The menu library first appeared in AT&T System V. The version
documented here is the menu code distributed with ncurses.
-Compiling With the menu Library
+ Compiling With the menu Library
Your menu-using modules must import the menu library declarations with
#include <menu.h>
-lncurses. Many linkers are two-pass and will accept either order, but
it is still good practice to put -lmenu first and -lncurses second.
-Overview of Menus
+ Overview of Menus
The menus created by this library consist of collections of items
including a name string part and a description string part. To make
9. Free the items using free_item().
10. Terminate curses.
-Selecting items
+ Selecting items
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
option so far defined for menus, but it is good practice to code as
though other option bits might be on.
-Menu Display
+ Menu Display
The menu library calculates a minimum display size for your window,
based on the following variables:
have reasonable defaults which the library allows you to change (see
the menu_attribs(3x) manual page.
-Menu Windows
+ Menu Windows
Each menu has, as mentioned previously, a pair of associated windows.
Both these windows are painted when the menu is posted and erased when
these actually modifies the screen. To do that, call wrefresh() or
some equivalent.
-Processing Menu Input
+ Processing Menu Input
The main loop of your menu-processing code should call menu_driver()
repeatedly. The first argument of this routine is a menu pointer; the
considered application-specific commands. The menu_driver() code
ignores them and returns E_UNKNOWN_COMMAND.
-Miscellaneous Other Features
+ Miscellaneous Other Features
Various menu options can affect the processing and visual appearance
and input processing of menus. See menu_opts(3x) for details.
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 Forms Library
+The Forms Library
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.
-Compiling With the form Library
+ Compiling With the form Library
Your form-using modules must import the form library declarations with
#include <form.h>
-lncurses. Many linkers are two-pass and will accept either order, but
it is still good practice to put -lform first and -lncurses second.
-Overview of Forms
+ Overview of Forms
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
operations, the menu driver loop has to support field editing and data
validation.
-Creating and Freeing Fields and Forms
+ Creating and Freeing Fields and Forms
The basic function for creating fields is new_field():
FIELD *new_field(int height, int width, /* new field size */
to a form, but not vice-versa; thus, you will generally free your form
objects first.
-Fetching and Changing Field Attributes
+ Fetching and Changing Field Attributes
Each form field has a number of location and size attributes
associated with it. There are other field attributes used to control
to mean this field. Changes to it persist as defaults until your forms
application terminates.
- Fetching Size and Location Data
+ Fetching Size and Location Data
You can retrieve field sizes and locations through:
int field_info(FIELD *field, /* field from which to fetch */
size and location attributes of a new field, it fetches them from an
existing one.
- Changing the Field Location
+ Changing the Field Location
It is possible to move a field's location on the screen:
int move_field(FIELD *field, /* field to alter */
You can, of course. query the current location through field_info().
- The Justification Attribute
+ The Justification Attribute
One-line fields may be unjustified, justified right, justified left,
or centered. Here is how you manipulate this attribute:
preprocessor macros NO_JUSTIFICATION, JUSTIFY_RIGHT, JUSTIFY_LEFT, or
JUSTIFY_CENTER.
- Field Display Attributes
+ Field Display Attributes
For each field, you can set a foreground attribute for entered
characters, a background attribute for the entire field, and a pad
etc). The page bit of a field controls whether it is displayed at the
start of a new form screen.
- Field Option Bits
+ Field Option Bits
There is also a large collection of field option bits you can set to
control various aspects of forms processing. You can manipulate them
The option values are bit-masks and can be composed with logical-or in
the obvious way.
-Field Status
+ Field Status
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
initialization or termination hooks, or (3) just after a
REQ_VALIDATION request has been processed by the forms driver.
-Field User Pointer
+ Field User Pointer
Each field structure contains one character pointer slot that is not
used by the forms library. It is intended to be used by applications
field is created, the default-field user pointer is copied to
initialize the new field's user pointer.
-Variable-Sized Fields
+ Variable-Sized Fields
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
the field; use dynamic_field_info() to get the actual dynamic
size.
-Field Validation
+ Field Validation
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
Here are the pre-defined validation types:
- TYPE_ALPHA
+ TYPE_ALPHA
This field type accepts alphabetic data; no blanks, no digits, no
special characters (this is checked at character-entry time). It is
width, the validation check will always fail. A minimum width of zero
makes field completion optional.
- TYPE_ALNUM
+ TYPE_ALNUM
This field type accepts alphabetic data and digits; no blanks, no
special characters (this is checked at character-entry time). It is
greater than the field width, the validation check will always fail. A
minimum width of zero makes field completion optional.
- TYPE_ENUM
+ TYPE_ENUM
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
The REQ_NEXT_CHOICE and REQ_PREV_CHOICE input requests can be
particularly useful with these fields.
- TYPE_INTEGER
+ TYPE_INTEGER
This field type accepts an integer. It is set up as follows:
int set_field_type(FIELD *field, /* field to alter */
A TYPE_INTEGER value buffer can conveniently be interpreted with the C
library function atoi(3).
- TYPE_NUMERIC
+ TYPE_NUMERIC
This field type accepts a decimal number. It is set up as follows:
int set_field_type(FIELD *field, /* field to alter */
A TYPE_NUMERIC value buffer can conveniently be interpreted with the C
library function atof(3).
- TYPE_REGEXP
+ TYPE_REGEXP
This field type accepts data matching a regular expression. It is set
up as follows:
The syntax for regular expressions is that of regcomp(3). The check
for regular-expression match is performed on exit.
-Direct Field Buffer Manipulation
+ Direct Field Buffer Manipulation
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
or form's initialization or termination hooks, or (3) just after a
REQ_VALIDATION request has been processed by the forms driver.
-Attributes of Forms
+ Attributes of Forms
As with field attributes, form attributes inherit a default from a
system default form structure. These defaults can be queried or set by
connected to a given from. It returns -1 if the form-pointer argument
is NULL.
-Control of Form Display
+ Control of Form Display
In the overview section, you saw that to display a form you normally
start by defining its size (and fields), posting it, and refreshing
before handing control back to the forms driver in order to
re-synchronize it.
-Input Processing in the Forms Driver
+ Input Processing in the Forms Driver
The function form_driver() handles virtualized input requests for form
navigation, editing, and validation requests, just as menu_driver does
field-termination functions) with which your application code can
check that the input taken by the driver matched what was expected.
- Page Navigation Requests
+ Page Navigation Requests
These requests cause page-level moves through the form, triggering
display of a new form screen.
the last page goes to the first, and REQ_PREV_PAGE from the first page
goes to the last.
- Inter-Field Navigation Requests
+ Inter-Field Navigation Requests
These requests handle navigation between fields on the same page.
only if A, B, and C all share the same first line; otherwise it will
skip over B to C.
- Intra-Field Navigation Requests
+ Intra-Field Navigation Requests
These requests drive movement of the edit cursor within the currently
selected field.
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.
- Scrolling Requests
+ Scrolling Requests
Fields that are dynamic and have grown and fields explicitly created
with offscreen rows are scrollable. One-line fields scroll
For scrolling purposes, a page of a field is the height of its visible
part.
- Editing Requests
+ Editing Requests
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
See Form Options for discussion of how to set and clear the overload
options.
- Order Requests
+ Order Requests
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,
Custom Validation Types), you can associate our own ordering
functions.
- Application Commands
+ Application Commands
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.
-Field Change Hooks
+ Field Change Hooks
It is possible to set function hooks to be executed whenever the
current field or form changes. Here are the functions that support
You can disable any of these hooks by (re)setting them to NULL, the
default value.
-Field Change Commands
+ Field Change Commands
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
The initial page of a newly-created form is 0. The function
set_form_fields() resets this.
-Form Options
+ Form Options
Like fields, forms may have control option bits. They can be changed
or queried with these functions:
The option values are bit-masks and can be composed with logical-or in
the obvious way.
-Custom Validation Types
+ Custom Validation Types
The form library gives you the capability to define custom validation
types of your own. Further, the optional additional arguments of
with the handling of the additional arguments within custom validation
functions.
- Union Types
+ Union Types
The simplest way to create a custom data type is to compose it from
two preexisting ones:
first type, then for the second, to figure what type the buffer
contents should be treated as.
- New Field Types
+ New Field Types
To create a field type from scratch, you need to specify one or both
of the following things:
argument. It too should return TRUE if the character is valid, FALSE
otherwise.
- Validation Function Arguments
+ Validation Function Arguments
Your field- and character- validation functions will be passed a
second argument as well. This second argument is the address of a
functions should never see a NULL file pointer and need not check
specially for it.
- Order Functions For Custom Types
+ Order Functions For Custom Types
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
success (a legal next or previous value was set) or FALSE to indicate
failure.
- Avoiding Problems
+ Avoiding Problems
The interface for defining custom types is complicated and tricky.
Rather than attempting to create a custom type entirely from scratch,
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