2503 lines
109 KiB
Plaintext
2503 lines
109 KiB
Plaintext
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Writing Programs with NCURSES
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by Eric S. Raymond and Zeyd M. Ben-Halim
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updates since release 1.9.9e by Thomas Dickey
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Contents
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* Introduction
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+ A Brief History of Curses
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+ Scope of This Document
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+ Terminology
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* The Curses Library
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+ An Overview of Curses
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o Compiling Programs using Curses
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o Updating the Screen
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o Standard Windows and Function Naming Conventions
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o Variables
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+ Using the Library
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o Starting up
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o Output
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o Input
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o Using Forms Characters
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o Character Attributes and Color
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o Mouse Interfacing
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o Finishing Up
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+ Function Descriptions
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o Initialization and Wrapup
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o Causing Output to the Terminal
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o Low-Level Capability Access
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o Debugging
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+ Hints, Tips, and Tricks
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o Some Notes of Caution
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o Temporarily Leaving ncurses Mode
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o Using ncurses under xterm
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o Handling Multiple Terminal Screens
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o Testing for Terminal Capabilities
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o Tuning for Speed
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o Special Features of ncurses
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+ Compatibility with Older Versions
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o Refresh of Overlapping Windows
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o Background Erase
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+ XSI Curses Conformance
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* The Panels Library
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+ Compiling With the Panels Library
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+ Overview of Panels
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+ Panels, Input, and the Standard Screen
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+ Hiding Panels
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+ Miscellaneous Other Facilities
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* The Menu Library
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+ Compiling with the menu Library
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+ Overview of Menus
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+ Selecting items
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+ Menu Display
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+ Menu Windows
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+ Processing Menu Input
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+ Miscellaneous Other Features
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* The Forms Library
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+ Compiling with the forms Library
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+ Overview of Forms
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+ Creating and Freeing Fields and Forms
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+ Fetching and Changing Field Attributes
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o Fetching Size and Location Data
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o Changing the Field Location
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o The Justification Attribute
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o Field Display Attributes
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o Field Option Bits
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o Field Status
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o Field User Pointer
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+ Variable-Sized Fields
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+ Field Validation
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o TYPE_ALPHA
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o TYPE_ALNUM
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o TYPE_ENUM
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o TYPE_INTEGER
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o TYPE_NUMERIC
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o TYPE_REGEXP
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+ Direct Field Buffer Manipulation
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+ Attributes of Forms
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+ Control of Form Display
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+ Input Processing in the Forms Driver
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o Page Navigation Requests
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o Inter-Field Navigation Requests
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o Intra-Field Navigation Requests
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o Scrolling Requests
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o Field Editing Requests
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o Order Requests
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o Application Commands
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+ Field Change Hooks
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+ Field Change Commands
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+ Form Options
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+ Custom Validation Types
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o Union Types
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o New Field Types
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o Validation Function Arguments
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o Order Functions For Custom Types
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o Avoiding Problems
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_________________________________________________________________
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Introduction
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This document is an introduction to programming with curses. It is not
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an exhaustive reference for the curses Application Programming
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Interface (API); that role is filled by the curses manual pages.
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Rather, it is intended to help C programmers ease into using the
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package.
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This document is aimed at C applications programmers not yet
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specifically familiar with ncurses. If you are already an experienced
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curses programmer, you should nevertheless read the sections on Mouse
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Interfacing, Debugging, Compatibility with Older Versions, and Hints,
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Tips, and Tricks. These will bring you up to speed on the special
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features and quirks of the ncurses implementation. If you are not so
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experienced, keep reading.
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The curses package is a subroutine library for terminal-independent
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screen-painting and input-event handling which presents a high level
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screen model to the programmer, hiding differences between terminal
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types and doing automatic optimization of output to change one screen
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full of text into another. Curses uses terminfo, which is a database
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format that can describe the capabilities of thousands of different
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terminals.
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The curses API may seem something of an archaism on UNIX desktops
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increasingly dominated by X, Motif, and Tcl/Tk. Nevertheless, UNIX
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still supports tty lines and X supports xterm(1); the curses API has
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the advantage of (a) back-portability to character-cell terminals, and
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(b) simplicity. For an application that does not require bit-mapped
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graphics and multiple fonts, an interface implementation using curses
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will typically be a great deal simpler and less expensive than one
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using an X toolkit.
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A Brief History of Curses
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Historically, the first ancestor of curses was the routines written to
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provide screen-handling for the game rogue; these used the
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already-existing termcap database facility for describing terminal
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capabilities. These routines were abstracted into a documented library
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and first released with the early BSD UNIX versions.
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System III UNIX from Bell Labs featured a rewritten and much-improved
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curses library. It introduced the terminfo format. Terminfo is based
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on Berkeley's termcap database, but contains a number of improvements
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and extensions. Parameterized capabilities strings were introduced,
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making it possible to describe multiple video attributes, and colors
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and to handle far more unusual terminals than possible with termcap.
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In the later AT&T System V releases, curses evolved to use more
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facilities and offer more capabilities, going far beyond BSD curses in
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power and flexibility.
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Scope of This Document
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This document describes ncurses, a free implementation of the System V
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curses API with some clearly marked extensions. It includes the
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following System V curses features:
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* Support for multiple screen highlights (BSD curses could only
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handle one `standout' highlight, usually reverse-video).
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* Support for line- and box-drawing using forms characters.
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* Recognition of function keys on input.
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* Color support.
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* Support for pads (windows of larger than screen size on which the
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screen or a subwindow defines a viewport).
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Also, this package makes use of the insert and delete line and
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character features of terminals so equipped, and determines how to
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optimally use these features with no help from the programmer. It
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allows arbitrary combinations of video attributes to be displayed,
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even on terminals that leave ``magic cookies'' on the screen to mark
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changes in attributes.
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The ncurses package can also capture and use event reports from a
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mouse in some environments (notably, xterm under the X window system).
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This document includes tips for using the mouse.
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The ncurses package was originated by Pavel Curtis. The original
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maintainer of this package is Zeyd Ben-Halim <zmbenhal@netcom.com>.
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Eric S. Raymond <esr@snark.thyrsus.com> wrote many of the new features
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in versions after 1.8.1 and wrote most of this introduction. J<>rgen
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Pfeifer wrote all of the menu and forms code as well as the Ada95
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binding. Ongoing work is being done by Thomas Dickey and J<>rgen
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Pfeifer. Florian La Roche acts as the maintainer for the Free Software
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Foundation, which holds the copyright on ncurses. Contact the current
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maintainers at bug-ncurses@gnu.org.
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This document also describes the panels extension library, similarly
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modeled on the SVr4 panels facility. This library allows you to
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associate backing store with each of a stack or deck of overlapping
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windows, and provides operations for moving windows around in the
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stack that change their visibility in the natural way (handling window
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overlaps).
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Finally, this document describes in detail the menus and forms
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extension libraries, also cloned from System V, which support easy
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construction and sequences of menus and fill-in forms.
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Terminology
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In this document, the following terminology is used with reasonable
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consistency:
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window
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A data structure describing a sub-rectangle of the screen
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(possibly the entire screen). You can write to a window as
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though it were a miniature screen, scrolling independently of
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other windows on the physical screen.
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screens
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A subset of windows which are as large as the terminal screen,
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i.e., they start at the upper left hand corner and encompass
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the lower right hand corner. One of these, stdscr, is
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automatically provided for the programmer.
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terminal screen
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The package's idea of what the terminal display currently looks
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like, i.e., what the user sees now. This is a special screen.
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The Curses Library
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An Overview of Curses
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Compiling Programs using Curses
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In order to use the library, it is necessary to have certain types and
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variables defined. Therefore, the programmer must have a line:
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#include <curses.h>
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at the top of the program source. The screen package uses the Standard
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I/O library, so <curses.h> includes <stdio.h>. <curses.h> also
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includes <termios.h>, <termio.h>, or <sgtty.h> depending on your
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system. It is redundant (but harmless) for the programmer to do these
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includes, too. In linking with curses you need to have -lncurses in
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your LDFLAGS or on the command line. There is no need for any other
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libraries.
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Updating the Screen
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In order to update the screen optimally, it is necessary for the
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routines to know what the screen currently looks like and what the
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programmer wants it to look like next. For this purpose, a data type
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(structure) named WINDOW is defined which describes a window image to
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the routines, including its starting position on the screen (the (y,
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x) coordinates of the upper left hand corner) and its size. One of
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these (called curscr, for current screen) is a screen image of what
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the terminal currently looks like. Another screen (called stdscr, for
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standard screen) is provided by default to make changes on.
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A window is a purely internal representation. It is used to build and
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store a potential image of a portion of the terminal. It doesn't bear
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any necessary relation to what is really on the terminal screen; it's
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more like a scratchpad or write buffer.
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To make the section of physical screen corresponding to a window
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reflect the contents of the window structure, the routine refresh()
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(or wrefresh() if the window is not stdscr) is called.
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A given physical screen section may be within the scope of any number
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of overlapping windows. Also, changes can be made to windows in any
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order, without regard to motion efficiency. Then, at will, the
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programmer can effectively say ``make it look like this,'' and let the
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package implementation determine the most efficient way to repaint the
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screen.
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Standard Windows and Function Naming Conventions
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As hinted above, the routines can use several windows, but two are
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automatically given: curscr, which knows what the terminal looks like,
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and stdscr, which is what the programmer wants the terminal to look
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like next. The user should never actually access curscr directly.
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Changes should be made to through the API, and then the routine
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refresh() (or wrefresh()) called.
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Many functions are defined to use stdscr as a default screen. For
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example, to add a character to stdscr, one calls addch() with the
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desired character as argument. To write to a different window. use the
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routine waddch() (for `w'indow-specific addch()) is provided. This
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convention of prepending function names with a `w' when they are to be
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applied to specific windows is consistent. The only routines which do
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not follow it are those for which a window must always be specified.
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In order to move the current (y, x) coordinates from one point to
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another, the routines move() and wmove() are provided. However, it is
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often desirable to first move and then perform some I/O operation. In
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order to avoid clumsiness, most I/O routines can be preceded by the
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prefix 'mv' and the desired (y, x) coordinates prepended to the
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arguments to the function. For example, the calls
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move(y, x);
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addch(ch);
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can be replaced by
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mvaddch(y, x, ch);
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and
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wmove(win, y, x);
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waddch(win, ch);
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can be replaced by
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mvwaddch(win, y, x, ch);
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Note that the window description pointer (win) comes before the added
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(y, x) coordinates. If a function requires a window pointer, it is
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always the first parameter passed.
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Variables
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The curses library sets some variables describing the terminal
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capabilities.
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type name description
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------------------------------------------------------------------
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int LINES number of lines on the terminal
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int COLS number of columns on the terminal
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The curses.h also introduces some #define constants and types of
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general usefulness:
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bool
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boolean type, actually a `char' (e.g., bool doneit;)
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TRUE
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boolean `true' flag (1).
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FALSE
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boolean `false' flag (0).
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ERR
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error flag returned by routines on a failure (-1).
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OK
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error flag returned by routines when things go right.
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Using the Library
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Now we describe how to actually use the screen package. In it, we
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assume all updating, reading, etc. is applied to stdscr. These
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instructions will work on any window, providing you change the
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function names and parameters as mentioned above.
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Here is a sample program to motivate the discussion:
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#include <curses.h>
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#include <signal.h>
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static void finish(int sig);
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int
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main(int argc, char *argv[])
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{
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int num = 0;
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/* initialize your non-curses data structures here */
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(void) signal(SIGINT, finish); /* arrange interrupts to terminate */
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(void) initscr(); /* initialize the curses library */
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keypad(stdscr, TRUE); /* enable keyboard mapping */
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(void) nonl(); /* tell curses not to do NL->CR/NL on output */
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(void) cbreak(); /* take input chars one at a time, no wait for \n */
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(void) echo(); /* echo input - in color */
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if (has_colors())
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{
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start_color();
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/*
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* Simple color assignment, often all we need. Color pair 0 cannot
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* be redefined. This example uses the same value for the color
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* pair as for the foreground color, though of course that is not
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* necessary:
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*/
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init_pair(1, COLOR_RED, COLOR_BLACK);
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init_pair(2, COLOR_GREEN, COLOR_BLACK);
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init_pair(3, COLOR_YELLOW, COLOR_BLACK);
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init_pair(4, COLOR_BLUE, COLOR_BLACK);
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init_pair(5, COLOR_CYAN, COLOR_BLACK);
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init_pair(6, COLOR_MAGENTA, COLOR_BLACK);
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init_pair(7, COLOR_WHITE, COLOR_BLACK);
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}
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for (;;)
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{
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int c = getch(); /* refresh, accept single keystroke of input */
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attrset(COLOR_PAIR(num % 8));
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num++;
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/* process the command keystroke */
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}
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finish(0); /* we're done */
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}
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static void finish(int sig)
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{
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endwin();
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/* do your non-curses wrapup here */
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exit(0);
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}
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Starting up
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In order to use the screen package, the routines must know about
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terminal characteristics, and the space for curscr and stdscr must be
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allocated. These function initscr() does both these things. Since it
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must allocate space for the windows, it can overflow memory when
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attempting to do so. On the rare occasions this happens, initscr()
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will terminate the program with an error message. initscr() must
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always be called before any of the routines which affect windows are
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used. If it is not, the program will core dump as soon as either
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curscr or stdscr are referenced. However, it is usually best to wait
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to call it until after you are sure you will need it, like after
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checking for startup errors. Terminal status changing routines like
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nl() and cbreak() should be called after initscr().
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Once the screen windows have been allocated, you can set them up for
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your program. If you want to, say, allow a screen to scroll, use
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scrollok(). If you want the cursor to be left in place after the last
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change, use leaveok(). If this isn't done, refresh() will move the
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cursor to the window's current (y, x) coordinates after updating it.
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You can create new windows of your own using the functions newwin(),
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derwin(), and subwin(). The routine delwin() will allow you to get rid
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of old windows. All the options described above can be applied to any
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window.
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Output
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Now that we have set things up, we will want to actually update the
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terminal. The basic functions used to change what will go on a window
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are addch() and move(). addch() adds a character at the current (y, x)
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coordinates. move() changes the current (y, x) coordinates to whatever
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you want them to be. It returns ERR if you try to move off the window.
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As mentioned above, you can combine the two into mvaddch() to do both
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things at once.
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The other output functions, such as addstr() and printw(), all call
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addch() to add characters to the window.
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After you have put on the window what you want there, when you want
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the portion of the terminal covered by the window to be made to look
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like it, you must call refresh(). In order to optimize finding
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changes, refresh() assumes that any part of the window not changed
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since the last refresh() of that window has not been changed on the
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terminal, i.e., that you have not refreshed a portion of the terminal
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with an overlapping window. If this is not the case, the routine
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touchwin() is provided to make it look like the entire window has been
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changed, thus making refresh() check the whole subsection of the
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terminal for changes.
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If you call wrefresh() with curscr as its argument, it will make the
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screen look like curscr thinks it looks like. This is useful for
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implementing a command which would redraw the screen in case it get
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messed up.
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Input
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The complementary function to addch() is getch() which, if echo is
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set, will call addch() to echo the character. Since the screen package
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needs to know what is on the terminal at all times, if characters are
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to be echoed, the tty must be in raw or cbreak mode. Since initially
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the terminal has echoing enabled and is in ordinary ``cooked'' mode,
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one or the other has to changed before calling getch(); otherwise, the
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program's output will be unpredictable.
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When you need to accept line-oriented input in a window, the functions
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wgetstr() and friends are available. There is even a wscanw() function
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that can do scanf()(3)-style multi-field parsing on window input.
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These pseudo-line-oriented functions turn on echoing while they
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execute.
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The example code above uses the call keypad(stdscr, TRUE) to enable
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support for function-key mapping. With this feature, the getch() code
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watches the input stream for character sequences that correspond to
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arrow and function keys. These sequences are returned as
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pseudo-character values. The #define values returned are listed in the
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curses.h The mapping from sequences to #define values is determined by
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key_ capabilities in the terminal's terminfo entry.
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Using Forms Characters
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The addch() function (and some others, including box() and border())
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can accept some pseudo-character arguments which are specially defined
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by ncurses. These are #define values set up in the curses.h header;
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see there for a complete list (look for the prefix ACS_).
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The most useful of the ACS defines are the forms-drawing characters.
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You can use these to draw boxes and simple graphs on the screen. If
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the terminal does not have such characters, curses.h will map them to
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a recognizable (though ugly) set of ASCII defaults.
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Character Attributes and Color
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The ncurses package supports screen highlights including standout,
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reverse-video, underline, and blink. It also supports color, which is
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treated as another kind of highlight.
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Highlights are encoded, internally, as high bits of the
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pseudo-character type (chtype) that curses.h uses to represent the
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contents of a screen cell. See the curses.h header file for a complete
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list of highlight mask values (look for the prefix A_).
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There are two ways to make highlights. One is to logical-or the value
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of the highlights you want into the character argument of an addch()
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call, or any other output call that takes a chtype argument.
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The other is to set the current-highlight value. This is logical-or'ed
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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.
|
||
|
||
Mouse Interfacing
|
||
|
||
The ncurses library also provides a mouse interface.
|
||
|
||
NOTE: this facility is specific to ncurses, it is not part of
|
||
either the XSI Curses standard, nor of System V Release 4, nor BSD
|
||
curses. System V Release 4 curses contains code with similar
|
||
interface definitions, however it is not documented. Other than by
|
||
disassembling the library, we have no way to determine exactly how
|
||
that mouse code works. Thus, we recommend that you wrap
|
||
mouse-related code in an #ifdef using the feature macro
|
||
NCURSES_MOUSE_VERSION so it will not be compiled and linked on
|
||
non-ncurses systems.
|
||
|
||
Presently, mouse event reporting works in the following environments:
|
||
* xterm and similar programs such as rxvt.
|
||
* Linux console, when configured with gpm(1), Alessandro Rubini's
|
||
mouse server.
|
||
* OS/2 EMX
|
||
|
||
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 touch-screens that can
|
||
return a pressure or duration parameter. There is also a device ID
|
||
field, which could be used to distinguish between multiple pointing
|
||
devices.
|
||
|
||
The class of visible events may be changed at any time via
|
||
mousemask(). Events that can be reported include presses, releases,
|
||
single-, double- and triple-clicks (you can set the maximum
|
||
button-down time for clicks). If you 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.
|
||
|
||
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()
|
||
was first called, and moves the cursor down to the lower-left corner.
|
||
Thus, anytime after the call to initscr, endwin() should be called
|
||
before exiting.
|
||
|
||
Function Descriptions
|
||
|
||
We describe the detailed behavior of some important curses functions
|
||
here, as a supplement to the manual page descriptions.
|
||
|
||
Initialization and Wrapup
|
||
|
||
initscr()
|
||
The first function called should almost always be initscr().
|
||
This will determine the terminal type and initialize curses
|
||
data structures. initscr() also arranges that the first call to
|
||
refresh() will clear the screen. If an error occurs a message
|
||
is written to standard error and the program exits. Otherwise
|
||
it returns a pointer to stdscr. A few functions may be called
|
||
before initscr (slk_init(), filter(), ripofflines(), use_env(),
|
||
and, if you are using multiple terminals, newterm().)
|
||
|
||
endwin()
|
||
Your program should always call endwin() before exiting or
|
||
shelling out of the program. This function will restore tty
|
||
modes, move the cursor to the lower left corner of the screen,
|
||
reset the terminal into the proper non-visual mode. Calling
|
||
refresh() or doupdate() after a temporary escape from the
|
||
program will restore the ncurses screen from before the escape.
|
||
|
||
newterm(type, ofp, ifp)
|
||
A program which outputs to more than one terminal should use
|
||
newterm() instead of initscr(). newterm() should be called once
|
||
for each terminal. It returns a variable of type SCREEN * which
|
||
should be saved as a reference to that terminal. The arguments
|
||
are the type of the terminal (a string) and FILE pointers for
|
||
the output and input of the terminal. If type is NULL then the
|
||
environment variable $TERM is used. endwin() should called once
|
||
at wrapup time for each terminal opened using this function.
|
||
|
||
set_term(new)
|
||
This function is used to switch to a different terminal
|
||
previously opened by newterm(). The screen reference for the
|
||
new terminal is passed as the parameter. The previous terminal
|
||
is returned by the function. All other calls affect only the
|
||
current terminal.
|
||
|
||
delscreen(sp)
|
||
The inverse of newterm(); deallocates the data structures
|
||
associated with a given SCREEN reference.
|
||
|
||
Causing Output to the Terminal
|
||
|
||
refresh() and wrefresh(win)
|
||
These functions must be called to actually get any output on
|
||
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.
|
||
|
||
doupdate() and wnoutrefresh(win)
|
||
These two functions allow multiple updates with more efficiency
|
||
than wrefresh. To use them, it is important to understand how
|
||
curses works. In addition to all the window structures, curses
|
||
keeps two data structures representing the terminal screen: a
|
||
physical screen, describing what is actually on the screen, and
|
||
a virtual screen, describing what the programmer wants to have
|
||
on the screen. wrefresh works by first copying the named window
|
||
to the virtual screen (wnoutrefresh()), and then calling the
|
||
routine to update the screen (doupdate()). If the programmer
|
||
wishes to output several windows at once, a series of calls to
|
||
wrefresh will result in alternating calls to wnoutrefresh() and
|
||
doupdate(), causing several bursts of output to the screen. By
|
||
calling wnoutrefresh() for each window, it is then possible to
|
||
call doupdate() once, resulting in only one burst of output,
|
||
with fewer total characters transmitted (this also avoids a
|
||
visually annoying flicker at each update).
|
||
|
||
Low-Level Capability Access
|
||
|
||
setupterm(term, filenum, errret)
|
||
This routine is called to initialize a terminal's description,
|
||
without setting up the curses screen structures or changing the
|
||
tty-driver mode bits. term is the character string representing
|
||
the name of the terminal being used. filenum is the UNIX file
|
||
descriptor of the terminal to be used for output. errret is a
|
||
pointer to an integer, in which a success or failure indication
|
||
is returned. The values returned can be 1 (all is well), 0 (no
|
||
such terminal), or -1 (some problem locating the terminfo
|
||
database).
|
||
|
||
The value of term can be given as NULL, which will cause the
|
||
value of TERM in the environment to be used. The errret pointer
|
||
can also be given as NULL, meaning no error code is wanted. If
|
||
errret is defaulted, and something goes wrong, setupterm() will
|
||
print an appropriate error message and exit, rather than
|
||
returning. Thus, a simple program can call setupterm(0, 1, 0)
|
||
and not worry about initialization errors.
|
||
|
||
After the call to setupterm(), the global variable cur_term is
|
||
set to point to the current structure of terminal capabilities.
|
||
By calling setupterm() for each terminal, and saving and
|
||
restoring cur_term, it is possible for a program to use two or
|
||
more terminals at once. Setupterm() also stores the names
|
||
section of the terminal description in the global character
|
||
array ttytype[]. Subsequent calls to setupterm() will overwrite
|
||
this array, so you'll have to save it yourself if need be.
|
||
|
||
Debugging
|
||
|
||
NOTE: These functions are not part of the standard curses API!
|
||
|
||
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
|
||
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
|
||
details. (It is also possible to set a trace level by assigning
|
||
a trace level value to the environment variable NCURSES_TRACE).
|
||
|
||
_tracef()
|
||
This function can be used to output your own debugging
|
||
information. It is only available only if you link with
|
||
-lncurses_g. It can be used the same way as printf(), only it
|
||
outputs a newline after the end of arguments. The output goes
|
||
to a file called trace in the current directory.
|
||
|
||
Trace logs can be difficult to interpret due to the sheer volume of
|
||
data dumped in them. There is a script called tracemunch included with
|
||
the ncurses distribution that can alleviate this problem somewhat; it
|
||
compacts long sequences of similar operations into more succinct
|
||
single-line pseudo-operations. These pseudo-ops can be distinguished
|
||
by the fact that they are named in capital letters.
|
||
|
||
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
|
||
|
||
If you find yourself thinking you need to use noraw() or nocbreak(),
|
||
think again and move carefully. It's probably better design to use
|
||
getstr() or one of its relatives to simulate cooked mode. The noraw()
|
||
and nocbreak() functions try to restore cooked mode, but they may end
|
||
up clobbering some control bits set before you started your
|
||
application. Also, they have always been poorly documented, and are
|
||
likely to hurt your application's usability with other curses
|
||
libraries.
|
||
|
||
Bear in mind that refresh() is a synonym for wrefresh(stdscr). 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 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.
|
||
|
||
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'
|
||
mode. A common reason for this is to support shell-out. This behavior
|
||
is simple to arrange in ncurses.
|
||
|
||
To leave ncurses mode, call endwin() as you would if you were
|
||
intending to terminate the program. This will take the screen back to
|
||
cooked mode; you can do your shell-out. When you want to return to
|
||
ncurses mode, simply call refresh() or doupdate(). This will repaint
|
||
the screen.
|
||
|
||
There is a boolean function, isendwin(), which code can use to test
|
||
whether ncurses screen mode is active. It returns TRUE in the interval
|
||
between an endwin() call and the following refresh(), FALSE otherwise.
|
||
|
||
Here is some sample code for shellout:
|
||
addstr("Shelling out...");
|
||
def_prog_mode(); /* save current tty modes */
|
||
endwin(); /* restore original tty modes */
|
||
system("sh"); /* run shell */
|
||
addstr("returned.\n"); /* prepare return message */
|
||
refresh(); /* restore save modes, repaint screen */
|
||
|
||
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.
|
||
|
||
That is the standard way, of course (it even works with some vendor's
|
||
curses implementations). Its drawback is that it clears the screen to
|
||
reinitialize the display, and does not resize subwindows which must be
|
||
shrunk. Ncurses provides an extension which works better, the
|
||
resizeterm function. That function ensures that all windows are
|
||
limited to the new screen dimensions, and pads stdscr with blanks if
|
||
the screen is larger.
|
||
|
||
Finally, ncurses can be configured to provide its own SIGWINCH
|
||
handler, based on resizeterm.
|
||
|
||
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
|
||
terminals, use newterm() directly.
|
||
|
||
For each call, you will have to specify a terminal type and a pair of
|
||
file pointers; each call will return a screen reference, and stdscr
|
||
will be set to the last one allocated. You will switch between screens
|
||
with the set_term call. Note that you will also have to call
|
||
def_shell_mode and def_prog_mode on each tty yourself.
|
||
|
||
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.
|
||
An easy way to do this is to call setupterm(), then use the functions
|
||
tigetflag(), tigetnum(), and tigetstr() to do your testing.
|
||
|
||
A particularly useful case of this often comes up when you want to
|
||
test whether a given terminal type should be treated as `smart'
|
||
(cursor-addressable) or `stupid'. The right way to test this is to see
|
||
if the return value of tigetstr("cup") is non-NULL. Alternatively, you
|
||
can include the term.h file and test the value of the macro
|
||
cursor_address.
|
||
|
||
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
|
||
the immedok() option!
|
||
|
||
Special Features of NCURSES
|
||
|
||
The wresize() function allows you to resize a window in place. The
|
||
associated resizeterm() function simplifies the construction of
|
||
SIGWINCH handlers, for resizing all windows.
|
||
|
||
The define_key() function allows you to define at runtime function-key
|
||
control sequences which are not in the terminal description. The
|
||
keyok() function allows you to temporarily enable or disable
|
||
interpretation of any function-key control sequence.
|
||
|
||
The use_default_colors() function allows you to construct applications
|
||
which can use the terminal's default foreground and background colors
|
||
as an additional "default" color. Several terminal emulators support
|
||
this feature, which is based on ISO 6429.
|
||
|
||
Ncurses supports up 16 colors, unlike SVr4 curses which defines only
|
||
8. While most terminals which provide color allow only 8 colors, about
|
||
a quarter (including XFree86 xterm) support 16 colors.
|
||
|
||
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
|
||
|
||
If you define two windows A and B that overlap, and then alternately
|
||
scribble on and refresh them, the changes made to the overlapping
|
||
region under historic curses versions were often not documented
|
||
precisely.
|
||
|
||
To understand why this is a problem, remember that screen updates are
|
||
calculated between two representations of the entire display. The
|
||
documentation says that when you refresh a window, it is first copied
|
||
to 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.
|
||
|
||
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
|
||
versions, erased areas of a window were filled with a blank modified
|
||
by the window's current attribute (as set by wattrset(), wattron(),
|
||
wattroff() and friends).
|
||
|
||
In newer versions, this is not so. Instead, the attribute of erased
|
||
blanks is normal unless and until it is modified by the functions
|
||
bkgdset() or wbkgdset().
|
||
|
||
This change in behavior conforms ncurses to System V Release 4 and the
|
||
XSI Curses standard.
|
||
|
||
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
|
||
fact, almost all features not directly concerned with wide characters
|
||
and internationalization) are also supported.
|
||
|
||
One effect of XSI conformance is the change in behavior described
|
||
under "Background Erase -- Compatibility with Old Versions".
|
||
|
||
Also, ncurses meets the XSI requirement that every macro entry point
|
||
have a corresponding function which may be linked (and will be
|
||
prototype-checked) if the macro definition is disabled with #undef.
|
||
|
||
The Panels Library
|
||
|
||
The ncurses library by itself provides good support for screen
|
||
displays in which the windows are tiled (non-overlapping). In the more
|
||
general case that windows may overlap, you have to use a series of
|
||
wnoutrefresh() calls followed by a doupdate(), and be careful about
|
||
the order you do the window refreshes in. It has to be bottom-upwards,
|
||
otherwise parts of windows that should be obscured will show through.
|
||
|
||
When your interface design is such that windows may dive deeper into
|
||
the visibility stack or pop to the top at runtime, the resulting
|
||
book-keeping can be tedious and difficult to get right. Hence the
|
||
panels library.
|
||
|
||
The panel library first appeared in AT&T System V. The version
|
||
documented here is the panel code distributed with ncurses.
|
||
|
||
Compiling With the Panels Library
|
||
|
||
Your panels-using modules must import the panels library declarations
|
||
with
|
||
#include <panel.h>
|
||
|
||
and must be linked explicitly with the panels library using an -lpanel
|
||
argument. Note that they must also link the ncurses library with
|
||
-lncurses. Many linkers are two-pass and will accept either order, but
|
||
it is still good practice to put -lpanel first and -lncurses second.
|
||
|
||
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
|
||
bottom-to-top visibility order. The panels library includes an update
|
||
function (analogous to refresh()) that displays all panels in the deck
|
||
in the proper order to resolve overlaps. The standard window, stdscr,
|
||
is considered below all panels.
|
||
|
||
Details on the panels functions are available in the man pages. We'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, you'll 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
|
||
code; this will work only if the argument window is either in the top
|
||
panel or unobscured by any other panels.
|
||
|
||
The stsdcr window is a special case. It is considered below all
|
||
panels. Because changes to panels may obscure parts of stdscr, though,
|
||
you should call update_panels() before doupdate() even when you only
|
||
change stdscr.
|
||
|
||
Note that wgetch automatically calls wrefresh. Therefore, before
|
||
requesting input from a panel window, you need to be sure that the
|
||
panel is totally unobscured.
|
||
|
||
There is presently no way to display changes to one obscured panel
|
||
without repainting all panels.
|
||
|
||
Hiding Panels
|
||
|
||
It's possible to remove a panel from the deck temporarily; use
|
||
hide_panel for this. Use show_panel() to render it visible again. The
|
||
predicate function panel_hidden tests whether or not a panel is
|
||
hidden.
|
||
|
||
The panel_update code ignores hidden panels. You cannot do top_panel()
|
||
or bottom_panel on a hidden panel(). Other panels operations are
|
||
applicable.
|
||
|
||
Miscellaneous Other Facilities
|
||
|
||
It's possible to navigate the deck using the functions panel_above()
|
||
and panel_below. Handed a panel pointer, they return the panel above
|
||
or below that panel. Handed NULL, they return the bottom-most or
|
||
top-most panel.
|
||
|
||
Every panel has an associated user pointer, not used by the panel
|
||
code, to which you can attach application data. See the man page
|
||
documentation of set_panel_userptr() and panel_userptr for details.
|
||
|
||
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
|
||
supports easy programming of menu hierarchies with a uniform but
|
||
flexible interface.
|
||
|
||
The menu library first appeared in AT&T System V. The version
|
||
documented here is the menu code distributed with ncurses.
|
||
|
||
Compiling With the menu Library
|
||
|
||
Your menu-using modules must import the menu library declarations with
|
||
#include <menu.h>
|
||
|
||
and must be linked explicitly with the menus library using an -lmenu
|
||
argument. Note that they must also link the ncurses library with
|
||
-lncurses. Many linkers are two-pass and will accept either order, but
|
||
it is still good practice to put -lmenu first and -lncurses second.
|
||
|
||
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
|
||
menus, you create groups of these items and connect them with menu
|
||
frame objects.
|
||
|
||
The menu can then by posted, that is written to an associated window.
|
||
Actually, each menu has two associated windows; a containing window in
|
||
which the programmer can scribble titles or borders, and a subwindow
|
||
in which the menu items proper are displayed. If this subwindow is too
|
||
small to display all the items, it will be a scrollable viewport on
|
||
the collection of items.
|
||
|
||
A menu may also be unposted (that is, undisplayed), and finally freed
|
||
to make the storage associated with it and its items available for
|
||
re-use.
|
||
|
||
The general flow of control of a menu program looks like this:
|
||
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().
|
||
5. Refresh the screen.
|
||
6. Process user requests via an input loop.
|
||
7. Unpost the menu using menu_unpost().
|
||
8. Free the menu, using free_menu().
|
||
9. Free the items using free_item().
|
||
10. Terminate curses.
|
||
|
||
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
|
||
types always have a current item.
|
||
|
||
From a single-valued menu you can read the selected value simply by
|
||
looking at the current item. From a multi-valued menu, you get the
|
||
selected set by looping through the items applying the item_value()
|
||
predicate function. Your menu-processing code can use the function
|
||
set_item_value() to flag the items in the select set.
|
||
|
||
Menu items can be made unselectable using set_item_opts() or
|
||
item_opts_off() with the O_SELECTABLE argument. This is the only
|
||
option so far defined for menus, but it is good practice to code as
|
||
though other option bits might be on.
|
||
|
||
Menu Display
|
||
|
||
The menu library calculates a minimum display size for your window,
|
||
based on the following variables:
|
||
* The number and maximum length of the menu items
|
||
* Whether the O_ROWMAJOR option is enabled
|
||
* Whether display of descriptions is enabled
|
||
* Whatever menu format may have been set by the programmer
|
||
* The length of the menu mark string used for highlighting selected
|
||
items
|
||
|
||
The function set_menu_format() allows you to set the maximum size of
|
||
the viewport or menu page that will be used to display menu items. You
|
||
can retrieve any format associated with a menu with menu_format(). The
|
||
default format is rows=16, columns=1.
|
||
|
||
The actual menu page may be smaller than the format size. This depends
|
||
on the item number and size and whether O_ROWMAJOR is on. This option
|
||
(on by default) causes menu items to be displayed in a `raster-scan'
|
||
pattern, so that if more than one item will fit horizontally the first
|
||
couple of items are side-by-side in the top row. The alternative is
|
||
column-major display, which tries to put the first several items in
|
||
the first column.
|
||
|
||
As mentioned above, a menu format not large enough to allow all items
|
||
to fit on-screen will result in a menu display that is vertically
|
||
scrollable.
|
||
|
||
You can scroll it with requests to the menu driver, which will be
|
||
described in the section on menu input handling.
|
||
|
||
Each menu has a mark string used to visually tag selected items; see
|
||
the menu_mark(3x) manual page for details. The mark string length also
|
||
influences the menu page size.
|
||
|
||
The function scale_menu() returns the minimum display size that the
|
||
menu code computes from all these factors. There are other menu
|
||
display attributes including a select attribute, an attribute for
|
||
selectable items, an attribute for unselectable items, and a pad
|
||
character used to separate item name text from description text. These
|
||
have reasonable defaults which the library allows you to change (see
|
||
the menu_attribs(3x) manual page.
|
||
|
||
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
|
||
the menu is unposted.
|
||
|
||
The outer or frame window is not otherwise touched by the menu
|
||
routines. It exists so the programmer can associate a title, a border,
|
||
or perhaps help text with the menu and have it properly refreshed or
|
||
erased at post/unpost time. The inner window or subwindow is where the
|
||
current menu page is displayed.
|
||
|
||
By default, both windows are stdscr. You can set them with the
|
||
functions in menu_win(3x).
|
||
|
||
When you call 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.
|
||
|
||
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
|
||
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.
|
||
|
||
Miscellaneous Other Features
|
||
|
||
Various menu options can affect the processing and visual appearance
|
||
and input processing of menus. See menu_opts(3x) for details.
|
||
|
||
It is possible to change the current item from application code; this
|
||
is useful if you want to write your own navigation requests. It is
|
||
also possible to explicitly set the top row of the menu display. See
|
||
mitem_current(3x). If your application needs to change the menu
|
||
subwindow cursor for any reason, pos_menu_cursor() will restore it to
|
||
the correct location for continuing menu driver processing.
|
||
|
||
It is possible to set hooks to be called at menu initialization and
|
||
wrapup time, and whenever the selected item changes. See
|
||
menu_hook(3x).
|
||
|
||
Each item, and each menu, has an associated user pointer on which you
|
||
can hang application data. See mitem_userptr(3x) and menu_userptr(3x).
|
||
|
||
The 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
|
||
|
||
Your form-using modules must import the form library declarations with
|
||
#include <form.h>
|
||
|
||
and must be linked explicitly with the forms library using an -lform
|
||
argument. Note that they must also link the ncurses library with
|
||
-lncurses. Many linkers are two-pass and will accept either order, but
|
||
it is still good practice to put -lform first and -lncurses second.
|
||
|
||
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
|
||
segmented into pages; each entry to a new page clears the screen.
|
||
|
||
To make forms, you create groups of fields and connect them with form
|
||
frame objects; the form library makes this relatively simple.
|
||
|
||
Once defined, a form can be posted, that is written to an associated
|
||
window. Actually, each form has two associated windows; a containing
|
||
window in which the programmer can scribble titles or borders, and a
|
||
subwindow in which the form fields proper are displayed.
|
||
|
||
As the form user fills out the posted form, navigation and editing
|
||
keys support movement between fields, editing keys support modifying
|
||
field, and plain text adds to or changes data in a current field. The
|
||
form library allows you (the forms designer) to bind each navigation
|
||
and editing key to any keystroke accepted by curses Fields may have
|
||
validation conditions on them, so that they check input data for type
|
||
and value. The form library supplies a rich set of pre-defined field
|
||
types, and makes it relatively easy to define new ones.
|
||
|
||
Once its transaction is completed (or aborted), a form may be unposted
|
||
(that is, undisplayed), and finally freed to make the storage
|
||
associated with it and its items available for re-use.
|
||
|
||
The general flow of control of a form program looks like this:
|
||
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().
|
||
5. Refresh the screen.
|
||
6. Process user requests via an input loop.
|
||
7. Unpost the form using form_unpost().
|
||
8. Free the form, using free_form().
|
||
9. Free the fields using free_field().
|
||
10. Terminate curses.
|
||
|
||
Note that this looks much like a menu program; the form library
|
||
handles tasks which are in many ways similar, and its interface was
|
||
obviously designed to resemble that of the menu library wherever
|
||
possible.
|
||
|
||
In forms programs, however, the `process user requests' is somewhat
|
||
more complicated than for menus. Besides menu-like navigation
|
||
operations, the menu driver loop has to support field editing and data
|
||
validation.
|
||
|
||
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 */
|
||
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 offscreen argument was
|
||
initially zero.
|
||
|
||
The forms library allocates one working buffer per field; the size of
|
||
each buffer is ((height + offscreen)*width + 1, one character for each
|
||
position in the field plus a NUL terminator. The sixth argument is the
|
||
number of additional data buffers to allocate for the field; your
|
||
application can use them for its own purposes.
|
||
FIELD *dup_field(FIELD *field, /* field to copy */
|
||
int top, int left); /* location of new copy */
|
||
|
||
The function dup_field() duplicates an existing field at a new
|
||
location. Size and buffering information are copied; some attribute
|
||
flags and status bits are not (see the form_field_new(3X) for
|
||
details).
|
||
FIELD *link_field(FIELD *field, /* field to copy */
|
||
int top, int left); /* location of new copy */
|
||
|
||
The function link_field() also duplicates an existing field at a new
|
||
location. The difference from dup_field() is that it arranges for the
|
||
new field's buffer to be shared with the old one.
|
||
|
||
Besides the obvious use in making a field editable from two different
|
||
form pages, linked fields give you a way to hack in dynamic labels. If
|
||
you declare several fields linked to an original, and then make them
|
||
inactive, changes from the original will still be propagated to the
|
||
linked fields.
|
||
|
||
As with duplicated fields, linked fields have attribute bits separate
|
||
from the original.
|
||
|
||
As you might guess, all these field-allocations return NULL if the
|
||
field allocation is not possible due to an out-of-memory error or
|
||
out-of-bounds arguments.
|
||
|
||
To connect fields to a form, use
|
||
FORM *new_form(FIELD **fields);
|
||
|
||
This function expects to see a NULL-terminated array of field
|
||
pointers. Said fields are connected to a newly-allocated form object;
|
||
its address is returned (or else NULL if the allocation fails).
|
||
|
||
Note that new_field() does not copy the pointer array into private
|
||
storage; if you modify the contents of the pointer array during forms
|
||
processing, all manner of bizarre things might happen. Also note that
|
||
any given field may only be connected to one form.
|
||
|
||
The functions free_field() and free_form are available to free field
|
||
and form objects. It is an error to attempt to free a field connected
|
||
to a form, but not vice-versa; thus, you will generally free your form
|
||
objects first.
|
||
|
||
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
|
||
display and editing of the field. Some (for example, the O_STATIC bit)
|
||
involve sufficient complications to be covered in sections of their
|
||
own later on. We cover the functions used to get and set several basic
|
||
attributes here.
|
||
|
||
When a field is created, the attributes not specified by the new_field
|
||
function are copied from an invisible system default field. In
|
||
attribute-setting and -fetching functions, the argument NULL is taken
|
||
to mean this field. Changes to it persist as defaults until your forms
|
||
application terminates.
|
||
|
||
Fetching Size and Location Data
|
||
|
||
You can retrieve field sizes and locations through:
|
||
int field_info(FIELD *field, /* field from which to fetch */
|
||
int *height, *int width, /* field size */
|
||
int *top, int *left, /* upper left corner */
|
||
int *offscreen, /* number of offscreen rows */
|
||
int *nbuf); /* number of working buffers */
|
||
|
||
This function is a sort of inverse of new_field(); instead of setting
|
||
size and location attributes of a new field, it fetches them from an
|
||
existing one.
|
||
|
||
Changing the Field Location
|
||
|
||
It is possible to move a field's location on the screen:
|
||
int move_field(FIELD *field, /* field to alter */
|
||
int top, int left); /* new upper-left corner */
|
||
|
||
You can, of course. query the current location through field_info().
|
||
|
||
The Justification Attribute
|
||
|
||
One-line fields may be unjustified, justified right, justified left,
|
||
or centered. Here is how you manipulate this attribute:
|
||
int set_field_just(FIELD *field, /* field to alter */
|
||
int justmode); /* mode to set */
|
||
|
||
int field_just(FIELD *field); /* fetch mode of field */
|
||
|
||
The mode values accepted and returned by this functions are
|
||
preprocessor macros NO_JUSTIFICATION, JUSTIFY_RIGHT, JUSTIFY_LEFT, or
|
||
JUSTIFY_CENTER.
|
||
|
||
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
|
||
character for the unfilled portion of the field. You can also control
|
||
pagination of the form.
|
||
|
||
This group of four field attributes controls the visual appearance of
|
||
the field on the screen, without affecting in any way the data in the
|
||
field buffer.
|
||
int set_field_fore(FIELD *field, /* field to alter */
|
||
chtype attr); /* attribute to set */
|
||
|
||
chtype field_fore(FIELD *field); /* field to query */
|
||
|
||
int set_field_back(FIELD *field, /* field to alter */
|
||
chtype attr); /* attribute to set */
|
||
|
||
chtype field_back(FIELD *field); /* field to query */
|
||
|
||
int set_field_pad(FIELD *field, /* field to alter */
|
||
int pad); /* pad character to set */
|
||
|
||
chtype field_pad(FIELD *field);
|
||
|
||
int set_new_page(FIELD *field, /* field to alter */
|
||
int flag); /* TRUE to force new page */
|
||
|
||
chtype new_page(FIELD *field); /* field to query */
|
||
|
||
The attributes set and returned by the first four functions are normal
|
||
curses(3x) display attribute values (A_STANDOUT, A_BOLD, A_REVERSE
|
||
etc). The page bit of a field controls whether it is displayed at the
|
||
start of a new form screen.
|
||
|
||
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
|
||
with these functions:
|
||
int set_field_opts(FIELD *field, /* field to alter */
|
||
int attr); /* attribute to set */
|
||
|
||
int field_opts_on(FIELD *field, /* field to alter */
|
||
int attr); /* attributes to turn on */
|
||
|
||
int field_opts_off(FIELD *field, /* field to alter */
|
||
int attr); /* attributes to turn off */
|
||
|
||
int field_opts(FIELD *field); /* field to query */
|
||
|
||
By default, all options are on. Here are the available option bits:
|
||
|
||
O_VISIBLE
|
||
Controls whether the field is visible on the screen. Can be
|
||
used during form processing to hide or pop up fields depending
|
||
on the value of parent fields.
|
||
|
||
O_ACTIVE
|
||
Controls whether the field is active during forms processing
|
||
(i.e. visited by form navigation keys). Can be used to make
|
||
labels or derived fields with buffer values alterable by the
|
||
forms application, not the user.
|
||
|
||
O_PUBLIC
|
||
Controls whether data is displayed during field entry. If this
|
||
option is turned off on a field, the library will accept and
|
||
edit data in that field, but it will not be displayed and the
|
||
visible field cursor will not move. You can turn off the
|
||
O_PUBLIC bit to define password fields.
|
||
|
||
O_EDIT
|
||
Controls whether the field's data can be modified. When this
|
||
option is off, all editing requests except REQ_PREV_CHOICE and
|
||
REQ_NEXT_CHOICE will fail. Such read-only fields may be useful
|
||
for help messages.
|
||
|
||
O_WRAP
|
||
Controls word-wrapping in multi-line fields. Normally, when any
|
||
character of a (blank-separated) word reaches the end of the
|
||
current line, the entire word is wrapped to the next line
|
||
(assuming there is one). When this option is off, the word will
|
||
be split across the line break.
|
||
|
||
O_BLANK
|
||
Controls field blanking. When this option is on, entering a
|
||
character at the first field position erases the entire field
|
||
(except for the just-entered character).
|
||
|
||
O_AUTOSKIP
|
||
Controls automatic skip to next field when this one fills.
|
||
Normally, when the forms user tries to type more data into a
|
||
field than will fit, the editing location jumps to next field.
|
||
When this option is off, the user's cursor will hang at the end
|
||
of the field. This option is ignored in dynamic fields that
|
||
have not reached their size limit.
|
||
|
||
O_NULLOK
|
||
Controls whether validation is applied to blank fields.
|
||
Normally, it is not; the user can leave a field blank without
|
||
invoking the usual validation check on exit. If this option is
|
||
off on a field, exit from it will invoke a validation check.
|
||
|
||
O_PASSOK
|
||
Controls whether validation occurs on every exit, or only after
|
||
the field is modified. Normally the latter is true. Setting
|
||
O_PASSOK may be useful if your field's validation function may
|
||
change during forms processing.
|
||
|
||
O_STATIC
|
||
Controls whether the field is fixed to its initial dimensions.
|
||
If you turn this off, the field becomes dynamic and will
|
||
stretch to fit entered data.
|
||
|
||
A field's options cannot be changed while the field is currently
|
||
selected. However, options may be changed on posted fields that are
|
||
not current.
|
||
|
||
The option values are bit-masks and can be composed with logical-or in
|
||
the obvious way.
|
||
|
||
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
|
||
can be queried and set directly:
|
||
int set_field_status(FIELD *field, /* field to alter */
|
||
int status); /* mode to set */
|
||
|
||
int field_status(FIELD *field); /* fetch mode of field */
|
||
|
||
Setting this flag under program control can be useful if you use the
|
||
same form repeatedly, looking for modified fields each time.
|
||
|
||
Calling field_status() on a field not currently selected for input
|
||
will return a correct value. Calling field_status() on a field that is
|
||
currently selected for input may not necessarily give a correct field
|
||
status value, because entered data 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.
|
||
|
||
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
|
||
to store private per-field data. You can manipulate it with:
|
||
int set_field_userptr(FIELD *field, /* field to alter */
|
||
char *userptr); /* mode to set */
|
||
|
||
char *field_userptr(FIELD *field); /* fetch mode of field */
|
||
|
||
(Properly, this user pointer field ought to have (void *) type. The
|
||
(char *) type is retained for System V compatibility.)
|
||
|
||
It is valid to set the user pointer of the default field (with a
|
||
set_field_userptr() call passed a NULL field pointer.) When a new
|
||
field is created, the default-field user pointer is copied to
|
||
initialize the new field's user pointer.
|
||
|
||
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
|
||
and will automatically resize itself to accommodate data as it is
|
||
entered. If the field has extra buffers associated with it, they will
|
||
grow right along with the main input buffer.
|
||
|
||
A one-line dynamic field will have a fixed height (1) but variable
|
||
width, scrolling horizontally to display data within the field area as
|
||
originally dimensioned and located. A multi-line dynamic field will
|
||
have a fixed width, but variable height (number of rows), scrolling
|
||
vertically to display data within the field area as originally
|
||
dimensioned and located.
|
||
|
||
Normally, a dynamic field is allowed to grow without limit. But it is
|
||
possible to set an upper limit on the size of a dynamic field. You do
|
||
it with this function:
|
||
int set_max_field(FIELD *field, /* field to alter (may not be NULL) */
|
||
int max_size); /* upper limit on field size */
|
||
|
||
If the field is one-line, max_size is taken to be a column size limit;
|
||
if it is multi-line, it is taken to be a line size limit. To disable
|
||
any limit, use an argument of zero. The growth limit can be changed
|
||
whether or not the O_STATIC bit is on, but has no effect until it is.
|
||
|
||
The following properties of a field change when it becomes dynamic:
|
||
* If there is no growth limit, there is no final position of the
|
||
field; therefore O_AUTOSKIP and O_NL_OVERLOAD are ignored.
|
||
* Field justification will be ignored (though whatever justification
|
||
is set up will be retained internally and can be queried).
|
||
* The dup_field() and link_field() calls copy dynamic-buffer sizes.
|
||
If the O_STATIC option is set on one of a collection of links,
|
||
buffer resizing will occur only when the field is edited through
|
||
that link.
|
||
* The call field_info() will retrieve the original static size of
|
||
the field; use dynamic_field_info() to get the actual dynamic
|
||
size.
|
||
|
||
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
|
||
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
|
||
validation types also have a character-validity check for each time a
|
||
character is entered in the field.
|
||
|
||
A field's validation check (if any) is not called when
|
||
set_field_buffer() modifies the input buffer, nor when that buffer is
|
||
changed through a linked field.
|
||
|
||
The form library provides a rich set of pre-defined validation types,
|
||
and gives you the capability to define custom ones of your own. You
|
||
can examine and change field validation attributes with the following
|
||
functions:
|
||
int set_field_type(FIELD *field, /* field to alter */
|
||
FIELDTYPE *ftype, /* type to associate */
|
||
...); /* additional arguments*/
|
||
|
||
FIELDTYPE *field_type(FIELD *field); /* field to query */
|
||
|
||
The validation type of a field is considered an attribute of the
|
||
field. As with other field attributes, Also, doing set_field_type()
|
||
with a NULL field default will change the system default for
|
||
validation of newly-created fields.
|
||
|
||
Here are the pre-defined validation types:
|
||
|
||
TYPE_ALPHA
|
||
|
||
This field type accepts alphabetic data; no blanks, no digits, no
|
||
special characters (this is checked at character-entry time). It is
|
||
set up with:
|
||
int set_field_type(FIELD *field, /* field to alter */
|
||
TYPE_ALPHA, /* type to associate */
|
||
int width); /* maximum width of field */
|
||
|
||
The width argument sets a minimum width of data. Typically you'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.
|
||
|
||
TYPE_ALNUM
|
||
|
||
This field type accepts alphabetic data and digits; no blanks, no
|
||
special characters (this is checked at character-entry time). It is
|
||
set up with:
|
||
int set_field_type(FIELD *field, /* field to alter */
|
||
TYPE_ALNUM, /* type to associate */
|
||
int width); /* maximum width of field */
|
||
|
||
The width argument sets a minimum width of data. As with TYPE_ALPHA,
|
||
typically you'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.
|
||
|
||
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
|
||
codes for U.S. states). It is set up with:
|
||
int set_field_type(FIELD *field, /* field to alter */
|
||
TYPE_ENUM, /* type to associate */
|
||
char **valuelist; /* list of possible values */
|
||
int checkcase; /* case-sensitive? */
|
||
int checkunique); /* must specify uniquely? */
|
||
|
||
The valuelist parameter must point at a NULL-terminated list of valid
|
||
strings. The checkcase argument, if true, makes comparison with the
|
||
string case-sensitive.
|
||
|
||
When the user exits a TYPE_ENUM field, the validation procedure tries
|
||
to complete the data in the buffer to a valid entry. If a complete
|
||
choice string has been entered, it is of course valid. But it is also
|
||
possible to enter a prefix of a valid string and have it completed for
|
||
you.
|
||
|
||
By default, if you enter such a prefix and it matches more than one
|
||
value in the string list, the prefix will be completed to the first
|
||
matching value. But the checkunique argument, if true, requires prefix
|
||
matches to be unique in order to be valid.
|
||
|
||
The REQ_NEXT_CHOICE and REQ_PREV_CHOICE input requests can be
|
||
particularly useful with these fields.
|
||
|
||
TYPE_INTEGER
|
||
|
||
This field type accepts an integer. It is set up as follows:
|
||
int set_field_type(FIELD *field, /* field to alter */
|
||
TYPE_INTEGER, /* type to associate */
|
||
int padding, /* # places to zero-pad to */
|
||
int vmin, int vmax); /* valid range */
|
||
|
||
Valid characters consist of an optional leading minus and digits. The
|
||
range check is performed on exit. If the range maximum is less than or
|
||
equal to the minimum, the range is ignored.
|
||
|
||
If the value passes its range check, it is padded with as many leading
|
||
zero digits as necessary to meet the padding argument.
|
||
|
||
A TYPE_INTEGER value buffer can conveniently be interpreted with the C
|
||
library function atoi(3).
|
||
|
||
TYPE_NUMERIC
|
||
|
||
This field type accepts a decimal number. It is set up as follows:
|
||
int set_field_type(FIELD *field, /* field to alter */
|
||
TYPE_NUMERIC, /* type to associate */
|
||
int padding, /* # places of precision */
|
||
double vmin, double vmax); /* valid range */
|
||
|
||
Valid characters consist of an optional leading minus and digits.
|
||
possibly including a decimal point. If your system supports locale's,
|
||
the decimal point character used must be the one defined by your
|
||
locale. The range check is performed on exit. If the range maximum is
|
||
less than or equal to the minimum, the range is ignored.
|
||
|
||
If the value passes its range check, it is padded with as many
|
||
trailing zero digits as necessary to meet the padding argument.
|
||
|
||
A TYPE_NUMERIC value buffer can conveniently be interpreted with the C
|
||
library function atof(3).
|
||
|
||
TYPE_REGEXP
|
||
|
||
This field type accepts data matching a regular expression. It is set
|
||
up as follows:
|
||
int set_field_type(FIELD *field, /* field to alter */
|
||
TYPE_REGEXP, /* type to associate */
|
||
char *regexp); /* expression to match */
|
||
|
||
The syntax for regular expressions is that of regcomp(3). The check
|
||
for regular-expression match is performed on exit.
|
||
|
||
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
|
||
each field buffer. You can find this out with:
|
||
char *field_buffer(FIELD *field, /* field to query */
|
||
int bufindex); /* number of buffer to query */
|
||
|
||
Normally, the state of the zero-numbered buffer for each field is set
|
||
by the user's editing actions on that field. It'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.
|
||
|
||
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
|
||
of these functions using a form-pointer argument of NULL.
|
||
|
||
The principal attribute of a form is its field list. You can query and
|
||
change this list with:
|
||
int set_form_fields(FORM *form, /* form to alter */
|
||
FIELD **fields); /* fields to connect */
|
||
|
||
char *form_fields(FORM *form); /* fetch fields of form */
|
||
|
||
int field_count(FORM *form); /* count connect fields */
|
||
|
||
The second argument of set_form_fields() may be a NULL-terminated
|
||
field pointer array like the one required by new_form(). In that case,
|
||
the old fields of the form are disconnected but not freed (and
|
||
eligible to be connected to other forms), then the new fields are
|
||
connected.
|
||
|
||
It may also be null, in which case the old fields are disconnected
|
||
(and not freed) but no new ones are connected.
|
||
|
||
The field_count() function simply counts the number of fields
|
||
connected to a given from. It returns -1 if the form-pointer argument
|
||
is NULL.
|
||
|
||
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
|
||
the screen. There is an hidden step before posting, which is the
|
||
association of the form with a frame window (actually, a pair of
|
||
windows) within which it will be displayed. By default, the forms
|
||
library associates every form with the full-screen window stdscr.
|
||
|
||
By making this step explicit, you can associate a form with a declared
|
||
frame window on your screen display. This can be useful if you want to
|
||
adapt the form display to different screen sizes, dynamically tile
|
||
forms on the screen, or use a form as part of an interface layout
|
||
managed by panels.
|
||
|
||
The two windows associated with each form have the same functions as
|
||
their analogues in the menu library. Both these windows are painted
|
||
when the form is posted and erased when the form is unposted.
|
||
|
||
The outer or frame window is not otherwise touched by the form
|
||
routines. It exists so the programmer can associate a title, a border,
|
||
or perhaps help text with the form and have it properly refreshed or
|
||
erased at post/unpost time. The inner window or subwindow is where the
|
||
current form page is actually displayed.
|
||
|
||
In order to declare your own frame window for a form, you'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.
|
||
|
||
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
|
||
for menus (see the section on menu input handling).
|
||
int form_driver(FORM *form, /* form to pass input to */
|
||
int request); /* form request code */
|
||
|
||
Your input virtualization function needs to take input and then
|
||
convert it to either an alphanumeric character (which is treated as
|
||
data to be entered in the currently-selected field), or a forms
|
||
processing request.
|
||
|
||
The forms driver provides hooks (through input-validation and
|
||
field-termination functions) with which your application code can
|
||
check that the input taken by the driver matched what was expected.
|
||
|
||
Page Navigation Requests
|
||
|
||
These requests cause page-level moves through the form, triggering
|
||
display of a new form screen.
|
||
|
||
REQ_NEXT_PAGE
|
||
Move to the next form page.
|
||
|
||
REQ_PREV_PAGE
|
||
Move to the previous form page.
|
||
|
||
REQ_FIRST_PAGE
|
||
Move to the first form page.
|
||
|
||
REQ_LAST_PAGE
|
||
Move to the last form page.
|
||
|
||
These requests treat the list as cyclic; that is, REQ_NEXT_PAGE from
|
||
the last page goes to the first, and REQ_PREV_PAGE from the first page
|
||
goes to the last.
|
||
|
||
Inter-Field Navigation Requests
|
||
|
||
These requests handle navigation between fields on the same page.
|
||
|
||
REQ_NEXT_FIELD
|
||
Move to next field.
|
||
|
||
REQ_PREV_FIELD
|
||
Move to previous field.
|
||
|
||
REQ_FIRST_FIELD
|
||
Move to the first field.
|
||
|
||
REQ_LAST_FIELD
|
||
Move to the last field.
|
||
|
||
REQ_SNEXT_FIELD
|
||
Move to sorted next field.
|
||
|
||
REQ_SPREV_FIELD
|
||
Move to sorted previous field.
|
||
|
||
REQ_SFIRST_FIELD
|
||
Move to the sorted first field.
|
||
|
||
REQ_SLAST_FIELD
|
||
Move to the sorted last field.
|
||
|
||
REQ_LEFT_FIELD
|
||
Move left to field.
|
||
|
||
REQ_RIGHT_FIELD
|
||
Move right to field.
|
||
|
||
REQ_UP_FIELD
|
||
Move up to field.
|
||
|
||
REQ_DOWN_FIELD
|
||
Move down to field.
|
||
|
||
These requests treat the list of fields on a page as cyclic; that is,
|
||
REQ_NEXT_FIELD from the last field goes to the first, and
|
||
REQ_PREV_FIELD from the first field goes to the last. The order of the
|
||
fields for these (and the REQ_FIRST_FIELD and REQ_LAST_FIELD requests)
|
||
is simply the order of the field pointers in the form array (as set up
|
||
by new_form() or set_form_fields()
|
||
|
||
It is also possible to traverse the fields as if they had been sorted
|
||
in screen-position order, so the sequence goes left-to-right and
|
||
top-to-bottom. To do this, use the second group of four
|
||
sorted-movement requests.
|
||
|
||
Finally, it is possible to move between fields using visual directions
|
||
up, down, right, and left. To accomplish this, use the third group of
|
||
four requests. Note, however, that the position of a form for purposes
|
||
of these requests is its upper-left corner.
|
||
|
||
For example, suppose you have a multi-line field B, and two
|
||
single-line fields A and C on the same line with B, with A to the left
|
||
of B and C to the right of B. A REQ_MOVE_RIGHT from A will go to B
|
||
only if A, B, and C all share the same first line; otherwise it will
|
||
skip over B to C.
|
||
|
||
Intra-Field Navigation Requests
|
||
|
||
These requests drive movement of the edit cursor within the currently
|
||
selected field.
|
||
|
||
REQ_NEXT_CHAR
|
||
Move to next character.
|
||
|
||
REQ_PREV_CHAR
|
||
Move to previous character.
|
||
|
||
REQ_NEXT_LINE
|
||
Move to next line.
|
||
|
||
REQ_PREV_LINE
|
||
Move to previous line.
|
||
|
||
REQ_NEXT_WORD
|
||
Move to next word.
|
||
|
||
REQ_PREV_WORD
|
||
Move to previous word.
|
||
|
||
REQ_BEG_FIELD
|
||
Move to beginning of field.
|
||
|
||
REQ_END_FIELD
|
||
Move to end of field.
|
||
|
||
REQ_BEG_LINE
|
||
Move to beginning of line.
|
||
|
||
REQ_END_LINE
|
||
Move to end of line.
|
||
|
||
REQ_LEFT_CHAR
|
||
Move left in field.
|
||
|
||
REQ_RIGHT_CHAR
|
||
Move right in field.
|
||
|
||
REQ_UP_CHAR
|
||
Move up in field.
|
||
|
||
REQ_DOWN_CHAR
|
||
Move down in field.
|
||
|
||
Each word is separated from the previous and next characters by
|
||
whitespace. The commands to move to beginning and end of line or field
|
||
look for the first or last non-pad character in their ranges.
|
||
|
||
Scrolling Requests
|
||
|
||
Fields that are dynamic and have grown and fields explicitly created
|
||
with offscreen rows are scrollable. One-line fields scroll
|
||
horizontally; multi-line fields scroll vertically. Most scrolling is
|
||
triggered by editing and intra-field movement (the library scrolls the
|
||
field to keep the cursor visible). It is possible to explicitly
|
||
request scrolling with the following requests:
|
||
|
||
REQ_SCR_FLINE
|
||
Scroll vertically forward a line.
|
||
|
||
REQ_SCR_BLINE
|
||
Scroll vertically backward a line.
|
||
|
||
REQ_SCR_FPAGE
|
||
Scroll vertically forward a page.
|
||
|
||
REQ_SCR_BPAGE
|
||
Scroll vertically backward a page.
|
||
|
||
REQ_SCR_FHPAGE
|
||
Scroll vertically forward half a page.
|
||
|
||
REQ_SCR_BHPAGE
|
||
Scroll vertically backward half a page.
|
||
|
||
REQ_SCR_FCHAR
|
||
Scroll horizontally forward a character.
|
||
|
||
REQ_SCR_BCHAR
|
||
Scroll horizontally backward a character.
|
||
|
||
REQ_SCR_HFLINE
|
||
Scroll horizontally one field width forward.
|
||
|
||
REQ_SCR_HBLINE
|
||
Scroll horizontally one field width backward.
|
||
|
||
REQ_SCR_HFHALF
|
||
Scroll horizontally one half field width forward.
|
||
|
||
REQ_SCR_HBHALF
|
||
Scroll horizontally one half field width backward.
|
||
|
||
For scrolling purposes, a page of a field is the height of its visible
|
||
part.
|
||
|
||
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
|
||
is an insertion or a replacement depends on the field's edit mode
|
||
(insertion is the default.
|
||
|
||
The following requests support editing the field and changing the edit
|
||
mode:
|
||
|
||
REQ_INS_MODE
|
||
Set insertion mode.
|
||
|
||
REQ_OVL_MODE
|
||
Set overlay mode.
|
||
|
||
REQ_NEW_LINE
|
||
New line request (see below for explanation).
|
||
|
||
REQ_INS_CHAR
|
||
Insert space at character location.
|
||
|
||
REQ_INS_LINE
|
||
Insert blank line at character location.
|
||
|
||
REQ_DEL_CHAR
|
||
Delete character at cursor.
|
||
|
||
REQ_DEL_PREV
|
||
Delete previous word at cursor.
|
||
|
||
REQ_DEL_LINE
|
||
Delete line at cursor.
|
||
|
||
REQ_DEL_WORD
|
||
Delete word at cursor.
|
||
|
||
REQ_CLR_EOL
|
||
Clear to end of line.
|
||
|
||
REQ_CLR_EOF
|
||
Clear to end of field.
|
||
|
||
REQ_CLEAR_FIELD
|
||
Clear entire field.
|
||
|
||
The behavior of the REQ_NEW_LINE and REQ_DEL_PREV requests is
|
||
complicated and partly controlled by a pair of forms options. The
|
||
special cases are triggered when the cursor is at the beginning of a
|
||
field, or on the last line of the field.
|
||
|
||
First, we consider REQ_NEW_LINE:
|
||
|
||
The normal behavior of REQ_NEW_LINE in insert mode is to break the
|
||
current line at the position of the edit cursor, inserting the portion
|
||
of the current line after the cursor as a new line following the
|
||
current and moving the cursor to the beginning of that new line (you
|
||
may think of this as inserting a newline in the field buffer).
|
||
|
||
The normal behavior of REQ_NEW_LINE in overlay mode is to clear the
|
||
current line from the position of the edit cursor to end of line. The
|
||
cursor is then moved to the beginning of the next line.
|
||
|
||
However, REQ_NEW_LINE at the beginning of a field, or on the last line
|
||
of a field, instead does a REQ_NEXT_FIELD. O_NL_OVERLOAD option is
|
||
off, this special action is disabled.
|
||
|
||
Now, let us consider REQ_DEL_PREV:
|
||
|
||
The normal behavior of REQ_DEL_PREV is to delete the previous
|
||
character. If insert mode is on, and the cursor is at the start of a
|
||
line, and the text on that line will fit on the previous one, it
|
||
instead appends the contents of the current line to the previous one
|
||
and deletes the current line (you may think of this as deleting a
|
||
newline from the field buffer).
|
||
|
||
However, REQ_DEL_PREV at the beginning of a field is instead treated
|
||
as a REQ_PREV_FIELD.
|
||
|
||
If the O_BS_OVERLOAD option is off, this special action is disabled
|
||
and the forms driver just returns E_REQUEST_DENIED.
|
||
|
||
See Form Options for discussion of how to set and clear the overload
|
||
options.
|
||
|
||
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,
|
||
there are requests that can fetch that value into the field buffer:
|
||
|
||
REQ_NEXT_CHOICE
|
||
Place the successor value of the current value in the buffer.
|
||
|
||
REQ_PREV_CHOICE
|
||
Place the predecessor value of the current value in the buffer.
|
||
|
||
Of the built-in field types, only TYPE_ENUM has built-in successor and
|
||
predecessor functions. When you define a field type of your own (see
|
||
Custom Validation Types), you can associate our own ordering
|
||
functions.
|
||
|
||
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
|
||
|
||
It is possible to set function hooks to be executed whenever the
|
||
current field or form changes. Here are the functions that support
|
||
this:
|
||
typedef void (*HOOK)(); /* pointer to function returning void */
|
||
|
||
int set_form_init(FORM *form, /* form to alter */
|
||
HOOK hook); /* initialization hook */
|
||
|
||
HOOK form_init(FORM *form); /* form to query */
|
||
|
||
int set_form_term(FORM *form, /* form to alter */
|
||
HOOK hook); /* termination hook */
|
||
|
||
HOOK form_term(FORM *form); /* form to query */
|
||
|
||
int set_field_init(FORM *form, /* form to alter */
|
||
HOOK hook); /* initialization hook */
|
||
|
||
HOOK field_init(FORM *form); /* form to query */
|
||
|
||
int set_field_term(FORM *form, /* form to alter */
|
||
HOOK hook); /* termination hook */
|
||
|
||
HOOK field_term(FORM *form); /* form to query */
|
||
|
||
These functions allow you to either set or query four different hooks.
|
||
In each of the set functions, the second argument should be the
|
||
address of a hook function. These functions differ only in the timing
|
||
of the hook call.
|
||
|
||
form_init
|
||
This hook is called when the form is posted; also, just after
|
||
each page change operation.
|
||
|
||
field_init
|
||
This hook is called when the form is posted; also, just after
|
||
each field change
|
||
|
||
field_term
|
||
This hook is called just after field validation; that is, just
|
||
before the field is altered. It is also called when the form is
|
||
unposted.
|
||
|
||
form_term
|
||
This hook is called when the form is unposted; also, just
|
||
before each page change operation.
|
||
|
||
Calls to these hooks may be triggered
|
||
1. When user editing requests are processed by the forms driver
|
||
2. When the current page is changed by set_current_field() call
|
||
3. When the current field is changed by a set_form_page() call
|
||
|
||
See Field Change Commands for discussion of the latter two cases.
|
||
|
||
You can set a default hook for all fields by passing one of the set
|
||
functions a NULL first argument.
|
||
|
||
You can disable any of these hooks by (re)setting them to NULL, the
|
||
default value.
|
||
|
||
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
|
||
focus for editing and viewing under control of your application, or
|
||
ask which field it currently is in. The following functions help you
|
||
accomplish this:
|
||
int set_current_field(FORM *form, /* form to alter */
|
||
FIELD *field); /* field to shift to */
|
||
|
||
FIELD *current_field(FORM *form); /* form to query */
|
||
|
||
int field_index(FORM *form, /* form to query */
|
||
FIELD *field); /* field to get index of */
|
||
|
||
The function field_index() returns the index of the given field in the
|
||
given form's field array (the array passed to new_form() or
|
||
set_form_fields()).
|
||
|
||
The initial current field of a form is the first active field on the
|
||
first page. The function set_form_fields() resets this.
|
||
|
||
It is also possible to move around by pages.
|
||
int set_form_page(FORM *form, /* form to alter */
|
||
int page); /* page to go to (0-origin) */
|
||
|
||
int form_page(FORM *form); /* return form's current page */
|
||
|
||
The initial page of a newly-created form is 0. The function
|
||
set_form_fields() resets this.
|
||
|
||
Form Options
|
||
|
||
Like fields, forms may have control option bits. They can be changed
|
||
or queried with these functions:
|
||
int set_form_opts(FORM *form, /* form to alter */
|
||
int attr); /* attribute to set */
|
||
|
||
int form_opts_on(FORM *form, /* form to alter */
|
||
int attr); /* attributes to turn on */
|
||
|
||
int form_opts_off(FORM *form, /* form to alter */
|
||
int attr); /* attributes to turn off */
|
||
|
||
int form_opts(FORM *form); /* form to query */
|
||
|
||
By default, all options are on. Here are the available option bits:
|
||
|
||
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
|
||
never arise.
|
||
|
||
O_BS_OVERLOAD
|
||
Enable overloading of REQ_DEL_PREV as described in Editing
|
||
Requests.
|
||
|
||
The option values are bit-masks and can be composed with logical-or in
|
||
the obvious way.
|
||
|
||
Custom Validation Types
|
||
|
||
The form library gives you the capability to define custom validation
|
||
types of your own. Further, the optional additional arguments of
|
||
set_field_type effectively allow you to parameterize validation types.
|
||
Most of the complications in the validation-type interface have to do
|
||
with the handling of the additional arguments within custom validation
|
||
functions.
|
||
|
||
Union Types
|
||
|
||
The simplest way to create a custom data type is to compose it from
|
||
two preexisting ones:
|
||
FIELD *link_fieldtype(FIELDTYPE *type1,
|
||
FIELDTYPE *type2);
|
||
|
||
This function creates a field type that will accept any of the values
|
||
legal for either of its argument field types (which may be either
|
||
predefined or programmer-defined). If a set_field_type() call later
|
||
requires arguments, the new composite type expects all arguments for
|
||
the first type, than all arguments for the second. Order functions
|
||
(see Order Requests) associated with the component types will work on
|
||
the composite; what it does is check the validation function for the
|
||
first type, then for the second, to figure what type the buffer
|
||
contents should be treated as.
|
||
|
||
New Field Types
|
||
|
||
To create a field type from scratch, you need to specify one or both
|
||
of the following things:
|
||
* A character-validation function, to check each character as it is
|
||
entered.
|
||
* A field-validation function to be applied on exit from the field.
|
||
|
||
Here's how you do that:
|
||
typedef int (*HOOK)(); /* pointer to function returning int */
|
||
|
||
FIELDTYPE *new_fieldtype(HOOK f_validate, /* field validator */
|
||
HOOK c_validate) /* character validator */
|
||
|
||
|
||
int free_fieldtype(FIELDTYPE *ftype); /* type to free */
|
||
|
||
At least one of the arguments of new_fieldtype() must be non-NULL. The
|
||
forms driver will automatically call the new type's validation
|
||
functions at appropriate points in processing a field of the new type.
|
||
|
||
The function free_fieldtype() deallocates the argument fieldtype,
|
||
freeing all storage associated with it.
|
||
|
||
Normally, a field validator is called when the user attempts to leave
|
||
the field. Its first argument is a field pointer, from which it can
|
||
get to field buffer 0 and test it. If the function returns TRUE, the
|
||
operation succeeds; if it returns FALSE, the edit cursor stays in the
|
||
field.
|
||
|
||
A character validator gets the character passed in as a first
|
||
argument. It too should return TRUE if the character is valid, FALSE
|
||
otherwise.
|
||
|
||
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
|
||
structure (which we'll call a pile) built from any of the
|
||
field-type-specific arguments passed to set_field_type(). If no such
|
||
arguments are defined for the field type, this pile pointer argument
|
||
will be NULL.
|
||
|
||
In order to arrange for such arguments to be passed to your validation
|
||
functions, you must associate a small set of storage-management
|
||
functions with the type. The forms driver will use these to synthesize
|
||
a pile from the trailing arguments of each set_field_type() argument,
|
||
and a pointer to the pile will be passed to the validation functions.
|
||
|
||
Here is how you make the association:
|
||
typedef char *(*PTRHOOK)(); /* pointer to function returning (char *) */
|
||
typedef void (*VOIDHOOK)(); /* pointer to function returning void */
|
||
|
||
int set_fieldtype_arg(FIELDTYPE *type, /* type to alter */
|
||
PTRHOOK make_str, /* make structure from args */
|
||
PTRHOOK copy_str, /* make copy of structure */
|
||
VOIDHOOK free_str); /* free structure storage */
|
||
|
||
Here is how the storage-management hooks are used:
|
||
|
||
make_str
|
||
This function is called by set_field_type(). It gets one
|
||
argument, a va_list of the type-specific arguments passed to
|
||
set_field_type(). It is expected to return a pile pointer to a
|
||
data structure that encapsulates those arguments.
|
||
|
||
copy_str
|
||
This function is called by form library functions that allocate
|
||
new field instances. It is expected to take a pile pointer,
|
||
copy the pile to allocated storage, and return the address of
|
||
the pile copy.
|
||
|
||
free_str
|
||
This function is called by field- and type-deallocation
|
||
routines in the library. It takes a pile pointer argument, and
|
||
is expected to free the storage of that pile.
|
||
|
||
The make_str and copy_str functions may return NULL to signal
|
||
allocation failure. The library routines will that call them will
|
||
return error indication when this happens. Thus, your validation
|
||
functions should never see a NULL file pointer and need not check
|
||
specially for it.
|
||
|
||
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
|
||
successor and predecessor functions to support the REQ_NEXT_CHOICE and
|
||
REQ_PREV_CHOICE requests. Here's how:
|
||
typedef int (*INTHOOK)(); /* pointer to function returning int */
|
||
|
||
int set_fieldtype_arg(FIELDTYPE *type, /* type to alter */
|
||
INTHOOK succ, /* get successor value */
|
||
INTHOOK pred); /* get predecessor value */
|
||
|
||
The successor and predecessor arguments will each be passed two
|
||
arguments; a field pointer, and a pile pointer (as for the validation
|
||
functions). They are expected to use the function field_buffer() to
|
||
read the current value, and set_field_buffer() on buffer 0 to set the
|
||
next or previous value. Either hook may return TRUE to indicate
|
||
success (a legal next or previous value was set) or FALSE to indicate
|
||
failure.
|
||
|
||
Avoiding Problems
|
||
|
||
The interface for defining custom types is complicated and tricky.
|
||
Rather than attempting to create a custom type entirely from scratch,
|
||
you should start by studying the library source code for whichever of
|
||
the pre-defined types seems to be closest to what you want.
|
||
|
||
Use that code as a model, and evolve it towards what you really want.
|
||
You will avoid many problems and annoyances that way. The code in the
|
||
ncurses library has been specifically exempted from the package
|
||
copyright to support this.
|
||
|
||
If your custom type defines order functions, have do something
|
||
intuitive with a blank field. A useful convention is to make the
|
||
successor of a blank field the types minimum value, and its
|
||
predecessor the maximum.
|