1                         Writing Programs with NCURSES
2
3     by Eric S. Raymond and Zeyd M. Ben-Halim
4     updates since release 1.9.9e by Thomas Dickey
5
6                                   Contents
7
8     * Introduction
9          + A Brief History of Curses
10          + Scope of This Document
11          + Terminology
12     * The Curses Library
13          + An Overview of Curses
14               o Compiling Programs using Curses
15               o Updating the Screen
16               o Standard Windows and Function Naming Conventions
17               o Variables
18          + Using the Library
19               o Starting up
20               o Output
21               o Input
22               o Using Forms Characters
23               o Character Attributes and Color
24               o Mouse Interfacing
25               o Finishing Up
26          + Function Descriptions
27               o Initialization and Wrapup
28               o Causing Output to the Terminal
29               o Low-Level Capability Access
30               o Debugging
31          + Hints, Tips, and Tricks
32               o Some Notes of Caution
33               o Temporarily Leaving ncurses Mode
34               o Using ncurses under xterm
35               o Handling Multiple Terminal Screens
36               o Testing for Terminal Capabilities
37               o Tuning for Speed
38               o Special Features of ncurses
39          + Compatibility with Older Versions
40               o Refresh of Overlapping Windows
41               o Background Erase
42          + XSI Curses Conformance
43     * The Panels Library
44          + Compiling With the Panels Library
45          + Overview of Panels
46          + Panels, Input, and the Standard Screen
47          + Hiding Panels
48          + Miscellaneous Other Facilities
49     * The Menu Library
50          + Compiling with the menu Library
51          + Overview of Menus
52          + Selecting items
53          + Menu Display
54          + Menu Windows
55          + Processing Menu Input
56          + Miscellaneous Other Features
57     * The Forms Library
58          + Compiling with the forms Library
59          + Overview of Forms
60          + Creating and Freeing Fields and Forms
61          + Fetching and Changing Field Attributes
62               o Fetching Size and Location Data
63               o Changing the Field Location
64               o The Justification Attribute
65               o Field Display Attributes
66               o Field Option Bits
67               o Field Status
68               o Field User Pointer
69          + Variable-Sized Fields
70          + Field Validation
71               o TYPE_ALPHA
72               o TYPE_ALNUM
73               o TYPE_ENUM
74               o TYPE_INTEGER
75               o TYPE_NUMERIC
76               o TYPE_REGEXP
77          + Direct Field Buffer Manipulation
78          + Attributes of Forms
79          + Control of Form Display
80          + Input Processing in the Forms Driver
81               o Page Navigation Requests
82               o Inter-Field Navigation Requests
83               o Intra-Field Navigation Requests
84               o Scrolling Requests
85               o Field Editing Requests
86               o Order Requests
87               o Application Commands
88          + Field Change Hooks
89          + Field Change Commands
90          + Form Options
91          + Custom Validation Types
92               o Union Types
93               o New Field Types
94               o Validation Function Arguments
95               o Order Functions For Custom Types
96               o Avoiding Problems
97     _________________________________________________________________
98
99                                 Introduction
100
101   This document is an introduction to programming with curses. It is not
102   an   exhaustive  reference  for  the  curses  Application  Programming
103   Interface  (API);  that  role  is  filled  by the curses manual pages.
104   Rather,  it  is  intended  to  help  C programmers ease into using the
105   package.
106
107   This   document  is  aimed  at  C  applications  programmers  not  yet
108   specifically  familiar with ncurses. If you are already an experienced
109   curses  programmer, you should nevertheless read the sections on Mouse
110   Interfacing,  Debugging, Compatibility with Older Versions, and Hints,
111   Tips,  and  Tricks.  These  will  bring you up to speed on the special
112   features  and  quirks of the ncurses implementation. If you are not so
113   experienced, keep reading.
114
115   The  curses  package  is a subroutine library for terminal-independent
116   screen-painting  and  input-event handling which presents a high level
117   screen  model  to  the programmer, hiding differences between terminal
118   types  and doing automatic optimization of output to change one screen
119   full  of  text into another. Curses uses terminfo, which is a database
120   format  that  can  describe the capabilities of thousands of different
121   terminals.
122
123   The  curses  API  may  seem  something of an archaism on UNIX desktops
124   increasingly  dominated  by  X,  Motif, and Tcl/Tk. Nevertheless, UNIX
125   still  supports  tty lines and X supports xterm(1); the curses API has
126   the advantage of (a) back-portability to character-cell terminals, and
127   (b)  simplicity.  For  an application that does not require bit-mapped
128   graphics  and multiple fonts, an interface implementation using curses
129   will  typically  be  a  great deal simpler and less expensive than one
130   using an X toolkit.
131
132A Brief History of Curses
133
134   Historically, the first ancestor of curses was the routines written to
135   provide   screen-handling   for   the   game  rogue;  these  used  the
136   already-existing  termcap  database  facility  for describing terminal
137   capabilities. These routines were abstracted into a documented library
138   and first released with the early BSD UNIX versions.
139
140   System  III UNIX from Bell Labs featured a rewritten and much-improved
141   curses  library.  It introduced the terminfo format. Terminfo is based
142   on  Berkeley's termcap database, but contains a number of improvements
143   and  extensions.  Parameterized  capabilities strings were introduced,
144   making  it  possible to describe multiple video attributes, and colors
145   and  to  handle far more unusual terminals than possible with termcap.
146   In  the  later  AT&T  System  V  releases,  curses evolved to use more
147   facilities and offer more capabilities, going far beyond BSD curses in
148   power and flexibility.
149
150Scope of This Document
151
152   This document describes ncurses, a free implementation of the System V
153   curses  API  with  some  clearly  marked  extensions.  It includes the
154   following System V curses features:
155     * Support  for  multiple  screen  highlights  (BSD curses could only
156       handle one `standout' highlight, usually reverse-video).
157     * Support for line- and box-drawing using forms characters.
158     * Recognition of function keys on input.
159     * Color support.
160     * Support  for pads (windows of larger than screen size on which the
161       screen or a subwindow defines a viewport).
162
163   Also,  this  package  makes  use  of  the  insert  and delete line and
164   character  features  of  terminals  so equipped, and determines how to
165   optimally  use  these  features  with  no help from the programmer. It
166   allows  arbitrary  combinations  of  video attributes to be displayed,
167   even  on  terminals that leave ``magic cookies'' on the screen to mark
168   changes in attributes.
169
170   The  ncurses  package  can  also  capture and use event reports from a
171   mouse in some environments (notably, xterm under the X window system).
172   This document includes tips for using the mouse.
173
174   The  ncurses  package  was  originated  by  Pavel Curtis. The original
175   maintainer  of  this  package is Zeyd Ben-Halim <zmbenhal@netcom.com>.
176   Eric S. Raymond <esr@snark.thyrsus.com> wrote many of the new features
177   in  versions  after 1.8.1 and wrote most of this introduction. Juergen
178   Pfeifer  wrote  all  of  the  menu and forms code as well as the Ada95
179   binding.  Ongoing  work  is  being done by Thomas Dickey (maintainer).
180   Contact the current maintainers at bug-ncurses@gnu.org.
181
182   This  document  also describes the panels extension library, similarly
183   modeled  on  the  SVr4  panels  facility.  This  library allows you to
184   associate  backing  store  with each of a stack or deck of overlapping
185   windows,  and  provides  operations  for  moving windows around in the
186   stack that change their visibility in the natural way (handling window
187   overlaps).
188
189   Finally,  this  document  describes  in  detail  the  menus  and forms
190   extension  libraries,  also  cloned  from System V, which support easy
191   construction and sequences of menus and fill-in forms.
192
193Terminology
194
195   In  this  document,  the following terminology is used with reasonable
196   consistency:
197
198   window
199          A  data  structure  describing  a  sub-rectangle  of the screen
200          (possibly  the  entire  screen).  You  can write to a window as
201          though  it  were a miniature screen, scrolling independently of
202          other windows on the physical screen.
203
204   screens
205          A  subset of windows which are as large as the terminal screen,
206          i.e.,  they  start  at the upper left hand corner and encompass
207          the   lower  right  hand  corner.  One  of  these,  stdscr,  is
208          automatically provided for the programmer.
209
210   terminal screen
211          The package's idea of what the terminal display currently looks
212          like, i.e., what the user sees now. This is a special screen.
213
214                              The Curses Library
215
216An Overview of Curses
217
218  Compiling Programs using Curses
219
220   In order to use the library, it is necessary to have certain types and
221   variables defined. Therefore, the programmer must have a line:
222          #include <curses.h>
223
224   at the top of the program source. The screen package uses the Standard
225   I/O   library,  so  <curses.h>  includes  <stdio.h>.  <curses.h>  also
226   includes  <termios.h>,  <termio.h>,  or  <sgtty.h>  depending  on your
227   system.  It is redundant (but harmless) for the programmer to do these
228   includes,  too.  In  linking with curses you need to have -lncurses in
229   your  LDFLAGS  or  on the command line. There is no need for any other
230   libraries.
231
232  Updating the Screen
233
234   In  order  to  update  the  screen  optimally, it is necessary for the
235   routines  to  know  what  the screen currently looks like and what the
236   programmer  wants  it to look like next. For this purpose, a data type
237   (structure)  named WINDOW is defined which describes a window image to
238   the  routines,  including its starting position on the screen (the (y,
239   x)  coordinates  of  the  upper left hand corner) and its size. One of
240   these  (called  curscr,  for current screen) is a screen image of what
241   the  terminal currently looks like. Another screen (called stdscr, for
242   standard screen) is provided by default to make changes on.
243
244   A  window is a purely internal representation. It is used to build and
245   store  a potential image of a portion of the terminal. It doesn't bear
246   any  necessary relation to what is really on the terminal screen; it's
247   more like a scratchpad or write buffer.
248
249   To  make  the  section  of  physical  screen corresponding to a window
250   reflect  the  contents  of the window structure, the routine refresh()
251   (or wrefresh() if the window is not stdscr) is called.
252
253   A  given physical screen section may be within the scope of any number
254   of  overlapping  windows.  Also, changes can be made to windows in any
255   order,  without  regard  to  motion  efficiency.  Then,  at  will, the
256   programmer can effectively say ``make it look like this,'' and let the
257   package implementation determine the most efficient way to repaint the
258   screen.
259
260  Standard Windows and Function Naming Conventions
261
262   As  hinted  above,  the  routines can use several windows, but two are
263   automatically given: curscr, which knows what the terminal looks like,
264   and  stdscr,  which  is what the programmer wants the terminal to look
265   like  next.  The  user  should  never actually access curscr directly.
266   Changes  should  be  made  to  through  the  API, and then the routine
267   refresh() (or wrefresh()) called.
268
269   Many  functions  are  defined  to  use stdscr as a default screen. For
270   example,  to  add  a  character  to stdscr, one calls addch() with the
271   desired character as argument. To write to a different window. use the
272   routine  waddch()  (for  `w'indow-specific  addch()) is provided. This
273   convention of prepending function names with a `w' when they are to be
274   applied  to specific windows is consistent. The only routines which do
275   not follow it are those for which a window must always be specified.
276
277   In  order  to  move  the  current (y, x) coordinates from one point to
278   another,  the routines move() and wmove() are provided. However, it is
279   often  desirable to first move and then perform some I/O operation. In
280   order  to  avoid  clumsiness, most I/O routines can be preceded by the
281   prefix  'mv'  and  the  desired  (y,  x)  coordinates prepended to the
282   arguments to the function. For example, the calls
283          move(y, x);
284          addch(ch);
285
286   can be replaced by
287          mvaddch(y, x, ch);
288
289   and
290          wmove(win, y, x);
291          waddch(win, ch);
292
293   can be replaced by
294          mvwaddch(win, y, x, ch);
295
296   Note  that the window description pointer (win) comes before the added
297   (y,  x)  coordinates.  If  a function requires a window pointer, it is
298   always the first parameter passed.
299
300  Variables
301
302   The  curses  library  sets  some  variables  describing  the  terminal
303   capabilities.
304      type   name      description
305      ------------------------------------------------------------------
306      int    LINES     number of lines on the terminal
307      int    COLS      number of columns on the terminal
308
309   The  curses.h  also  introduces  some  #define  constants and types of
310   general usefulness:
311
312   bool
313          boolean type, actually a `char' (e.g., bool doneit;)
314
315   TRUE
316          boolean `true' flag (1).
317
318   FALSE
319          boolean `false' flag (0).
320
321   ERR
322          error flag returned by routines on a failure (-1).
323
324   OK
325          error flag returned by routines when things go right.
326
327Using the Library
328
329   Now  we  describe  how  to  actually use the screen package. In it, we
330   assume  all  updating,  reading,  etc.  is  applied  to  stdscr. These
331   instructions  will  work  on  any  window,  providing  you  change the
332   function names and parameters as mentioned above.
333
334   Here is a sample program to motivate the discussion:
335#include <curses.h>
336#include <signal.h>
337
338static void finish(int sig);
339
340int
341main(int argc, char *argv[])
342{
343    int num = 0;
344
345    /* initialize your non-curses data structures here */
346
347    (void) signal(SIGINT, finish);      /* arrange interrupts to terminate */
348
349    (void) initscr();      /* initialize the curses library */
350    keypad(stdscr, TRUE);  /* enable keyboard mapping */
351    (void) nonl();         /* tell curses not to do NL->CR/NL on output */
352    (void) cbreak();       /* take input chars one at a time, no wait for \n */
353    (void) echo();         /* echo input - in color */
354
355    if (has_colors())
356    {
357        start_color();
358
359        /*
360         * Simple color assignment, often all we need.  Color pair 0 cannot
361         * be redefined.  This example uses the same value for the color
362         * pair as for the foreground color, though of course that is not
363         * necessary:
364         */
365        init_pair(1, COLOR_RED,     COLOR_BLACK);
366        init_pair(2, COLOR_GREEN,   COLOR_BLACK);
367        init_pair(3, COLOR_YELLOW,  COLOR_BLACK);
368        init_pair(4, COLOR_BLUE,    COLOR_BLACK);
369        init_pair(5, COLOR_CYAN,    COLOR_BLACK);
370        init_pair(6, COLOR_MAGENTA, COLOR_BLACK);
371        init_pair(7, COLOR_WHITE,   COLOR_BLACK);
372    }
373
374    for (;;)
375    {
376        int c = getch();     /* refresh, accept single keystroke of input */
377        attrset(COLOR_PAIR(num % 8));
378        num++;
379
380        /* process the command keystroke */
381    }
382
383    finish(0);               /* we're done */
384}
385
386static void finish(int sig)
387{
388    endwin();
389
390    /* do your non-curses wrapup here */
391
392    exit(0);
393}
394
395  Starting up
396
397   In  order  to  use  the  screen  package, the routines must know about
398   terminal  characteristics, and the space for curscr and stdscr must be
399   allocated.  These  function initscr() does both these things. Since it
400   must  allocate  space  for  the  windows,  it can overflow memory when
401   attempting  to  do  so.  On the rare occasions this happens, initscr()
402   will  terminate  the  program  with  an  error message. initscr() must
403   always  be  called before any of the routines which affect windows are
404   used.  If  it  is  not,  the  program will core dump as soon as either
405   curscr  or  stdscr are referenced. However, it is usually best to wait
406   to  call  it  until  after  you  are sure you will need it, like after
407   checking  for  startup  errors. Terminal status changing routines like
408   nl() and cbreak() should be called after initscr().
409
410   Once  the  screen windows have been allocated, you can set them up for
411   your  program.  If  you  want  to,  say, allow a screen to scroll, use
412   scrollok().  If you want the cursor to be left in place after the last
413   change,  use  leaveok().  If  this isn't done, refresh() will move the
414   cursor to the window's current (y, x) coordinates after updating it.
415
416   You  can  create new windows of your own using the functions newwin(),
417   derwin(), and subwin(). The routine delwin() will allow you to get rid
418   of  old windows. All the options described above can be applied to any
419   window.
420
421  Output
422
423   Now  that  we  have set things up, we will want to actually update the
424   terminal.  The basic functions used to change what will go on a window
425   are addch() and move(). addch() adds a character at the current (y, x)
426   coordinates. move() changes the current (y, x) coordinates to whatever
427   you want them to be. It returns ERR if you try to move off the window.
428   As  mentioned above, you can combine the two into mvaddch() to do both
429   things at once.
430
431   The  other  output  functions, such as addstr() and printw(), all call
432   addch() to add characters to the window.
433
434   After  you  have  put on the window what you want there, when you want
435   the  portion  of the terminal covered by the window to be made to look
436   like  it,  you  must  call  refresh().  In  order  to optimize finding
437   changes,  refresh()  assumes  that  any part of the window not changed
438   since  the  last  refresh() of that window has not been changed on the
439   terminal,  i.e., that you have not refreshed a portion of the terminal
440   with  an  overlapping  window.  If  this  is not the case, the routine
441   touchwin() is provided to make it look like the entire window has been
442   changed,  thus  making  refresh()  check  the  whole subsection of the
443   terminal for changes.
444
445   If  you  call wrefresh() with curscr as its argument, it will make the
446   screen  look  like  curscr  thinks  it  looks like. This is useful for
447   implementing  a  command  which would redraw the screen in case it get
448   messed up.
449
450  Input
451
452   The  complementary  function  to  addch() is getch() which, if echo is
453   set, will call addch() to echo the character. Since the screen package
454   needs  to know what is on the terminal at all times, if characters are
455   to  be  echoed, the tty must be in raw or cbreak mode. Since initially
456   the  terminal  has echoing enabled and is in ordinary ``cooked'' mode,
457   one or the other has to changed before calling getch(); otherwise, the
458   program's output will be unpredictable.
459
460   When you need to accept line-oriented input in a window, the functions
461   wgetstr() and friends are available. There is even a wscanw() function
462   that  can  do  scanf()(3)-style  multi-field  parsing on window input.
463   These  pseudo-line-oriented  functions  turn  on  echoing  while  they
464   execute.
465
466   The  example  code  above uses the call keypad(stdscr, TRUE) to enable
467   support  for function-key mapping. With this feature, the getch() code
468   watches  the  input  stream for character sequences that correspond to
469   arrow   and   function   keys.   These   sequences   are  returned  as
470   pseudo-character values. The #define values returned are listed in the
471   curses.h The mapping from sequences to #define values is determined by
472   key_ capabilities in the terminal's terminfo entry.
473
474  Using Forms Characters
475
476   The  addch()  function (and some others, including box() and border())
477   can accept some pseudo-character arguments which are specially defined
478   by  ncurses.  These  are #define values set up in the curses.h header;
479   see there for a complete list (look for the prefix ACS_).
480
481   The  most  useful of the ACS defines are the forms-drawing characters.
482   You  can  use  these to draw boxes and simple graphs on the screen. If
483   the  terminal does not have such characters, curses.h will map them to
484   a recognizable (though ugly) set of ASCII defaults.
485
486  Character Attributes and Color
487
488   The  ncurses  package  supports  screen highlights including standout,
489   reverse-video,  underline, and blink. It also supports color, which is
490   treated as another kind of highlight.
491
492   Highlights   are   encoded,   internally,   as   high   bits   of  the
493   pseudo-character  type  (chtype)  that  curses.h uses to represent the
494   contents of a screen cell. See the curses.h header file for a complete
495   list of highlight mask values (look for the prefix A_).
496
497   There  are two ways to make highlights. One is to logical-or the value
498   of  the  highlights you want into the character argument of an addch()
499   call, or any other output call that takes a chtype argument.
500
501   The other is to set the current-highlight value. This is logical-or'ed
502   with  any  highlight  you  specify the first way. You do this with the
503   functions attron(), attroff(), and attrset(); see the manual pages for
504   details.  Color  is  a special kind of highlight. The package actually
505   thinks  in  terms  of  color  pairs,  combinations  of  foreground and
506   background  colors.  The  sample code above sets up eight color pairs,
507   all  of the guaranteed-available colors on black. Note that each color
508   pair  is, in effect, given the name of its foreground color. Any other
509   range  of  eight  non-conflicting  values  could have been used as the
510   first arguments of the init_pair() values.
511
512   Once you've done an init_pair() that creates color-pair N, you can use
513   COLOR_PAIR(N)  as  a  highlight  that  invokes  that  particular color
514   combination.  Note  that  COLOR_PAIR(N),  for  constant N, is itself a
515   compile-time constant and can be used in initializers.
516
517  Mouse Interfacing
518
519   The ncurses library also provides a mouse interface.
520
521     NOTE:  this  facility  is  specific  to  ncurses, it is not part of
522     either  the XSI Curses standard, nor of System V Release 4, nor BSD
523     curses.  System  V  Release  4  curses  contains  code with similar
524     interface  definitions, however it is not documented. Other than by
525     disassembling  the library, we have no way to determine exactly how
526     that   mouse   code   works.  Thus,  we  recommend  that  you  wrap
527     mouse-related   code   in   an   #ifdef  using  the  feature  macro
528     NCURSES_MOUSE_VERSION  so  it  will  not  be compiled and linked on
529     non-ncurses systems.
530
531   Presently, mouse event reporting works in the following environments:
532     * xterm and similar programs such as rxvt.
533     * Linux  console,  when  configured with gpm(1), Alessandro Rubini's
534       mouse server.
535     * FreeBSD sysmouse (console)
536     * OS/2 EMX
537
538   The  mouse  interface  is  very  simple.  To  activate it, you use the
539   function  mousemask(),  passing  it  as first argument a bit-mask that
540   specifies  what  kinds  of  events you want your program to be able to
541   see.  It  will  return  the  bit-mask  of  events that actually become
542   visible, which may differ from the argument if the mouse device is not
543   capable of reporting some of the event types you specify.
544
545   Once the mouse is active, your application's command loop should watch
546   for  a  return  value of KEY_MOUSE from wgetch(). When you see this, a
547   mouse  event report has been queued. To pick it off the queue, use the
548   function  getmouse()  (you  must  do  this  before  the next wgetch(),
549   otherwise  another  mouse  event  might come in and make the first one
550   inaccessible).
551
552   Each call to getmouse() fills a structure (the address of which you'll
553   pass  it)  with mouse event data. The event data includes zero-origin,
554   screen-relative  character-cell  coordinates  of the mouse pointer. It
555   also  includes  an  event  mask.  Bits  in  this  mask  will  be  set,
556   corresponding to the event type being reported.
557
558   The  mouse  structure  contains  two  additional  fields  which may be
559   significant  in  the  future  as  ncurses  interfaces  to new kinds of
560   pointing  device.  In addition to x and y coordinates, there is a slot
561   for  a  z coordinate; this might be useful with touch-screens that can
562   return  a  pressure  or  duration parameter. There is also a device ID
563   field,  which  could  be used to distinguish between multiple pointing
564   devices.
565
566   The   class  of  visible  events  may  be  changed  at  any  time  via
567   mousemask().  Events  that  can be reported include presses, releases,
568   single-,   double-   and   triple-clicks  (you  can  set  the  maximum
569   button-down  time  for clicks). If you don't make clicks visible, they
570   will  be  reported  as  press-release pairs. In some environments, the
571   event  mask  may  include  bits reporting the state of shift, alt, and
572   ctrl keys on the keyboard during the event.
573
574   A  function  to check whether a mouse event fell within a given window
575   is  also  supplied.  You  can  use  this to see whether a given window
576   should consider a mouse event relevant to it.
577
578   Because   mouse   event   reporting  will  not  be  available  in  all
579   environments,  it  would  be unwise to build ncurses applications that
580   require  the  use  of  a  mouse. Rather, you should use the mouse as a
581   shortcut  for point-and-shoot commands your application would normally
582   accept  from  the  keyboard.  Two  of  the  test  games in the ncurses
583   distribution  (bs  and  knight) contain code that illustrates how this
584   can be done.
585
586   See   the   manual   page  curs_mouse(3X)  for  full  details  of  the
587   mouse-interface functions.
588
589  Finishing Up
590
591   In  order to clean up after the ncurses routines, the routine endwin()
592   is  provided.  It  restores tty modes to what they were when initscr()
593   was  first called, and moves the cursor down to the lower-left corner.
594   Thus,  anytime  after  the  call to initscr, endwin() should be called
595   before exiting.
596
597Function Descriptions
598
599   We  describe  the detailed behavior of some important curses functions
600   here, as a supplement to the manual page descriptions.
601
602  Initialization and Wrapup
603
604   initscr()
605          The  first  function  called should almost always be initscr().
606          This  will  determine  the  terminal type and initialize curses
607          data structures. initscr() also arranges that the first call to
608          refresh()  will  clear the screen. If an error occurs a message
609          is  written  to standard error and the program exits. Otherwise
610          it  returns  a pointer to stdscr. A few functions may be called
611          before  initscr (slk_init(), filter(), ripoffline(), use_env(),
612          and, if you are using multiple terminals, newterm().)
613
614   endwin()
615          Your  program  should  always  call  endwin() before exiting or
616          shelling  out  of  the  program. This function will restore tty
617          modes,  move the cursor to the lower left corner of the screen,
618          reset  the  terminal  into  the proper non-visual mode. Calling
619          refresh()  or  doupdate()  after  a  temporary  escape from the
620          program will restore the ncurses screen from before the escape.
621
622   newterm(type, ofp, ifp)
623          A  program  which  outputs to more than one terminal should use
624          newterm() instead of initscr(). newterm() should be called once
625          for each terminal. It returns a variable of type SCREEN * which
626          should  be  saved  as  a  reference  to that terminal. (NOTE: a
627          SCREEN  variable is not a screen in the sense we are describing
628          in  this  introduction,  but a collection of parameters used to
629          assist  in  optimizing the display.) The arguments are the type
630          of the terminal (a string) and FILE pointers for the output and
631          input  of  the  terminal.  If type is NULL then the environment
632          variable  $TERM  is used. endwin() should called once at wrapup
633          time for each terminal opened using this function.
634
635   set_term(new)
636          This  function  is  used  to  switch  to  a  different terminal
637          previously  opened  by  newterm(). The screen reference for the
638          new  terminal is passed as the parameter. The previous terminal
639          is  returned  by  the function. All other calls affect only the
640          current terminal.
641
642   delscreen(sp)
643          The  inverse  of  newterm();  deallocates  the  data structures
644          associated with a given SCREEN reference.
645
646  Causing Output to the Terminal
647
648   refresh() and wrefresh(win)
649          These  functions  must  be called to actually get any output on
650          the   terminal,   as  other  routines  merely  manipulate  data
651          structures.  wrefresh() copies the named window to the physical
652          terminal  screen,  taking into account what is already there in
653          order  to do optimizations. refresh() does a refresh of stdscr.
654          Unless  leaveok()  has been enabled, the physical cursor of the
655          terminal is left at the location of the window's cursor.
656
657   doupdate() and wnoutrefresh(win)
658          These two functions allow multiple updates with more efficiency
659          than  wrefresh.  To use them, it is important to understand how
660          curses  works. In addition to all the window structures, curses
661          keeps  two  data structures representing the terminal screen: a
662          physical screen, describing what is actually on the screen, and
663          a  virtual screen, describing what the programmer wants to have
664          on the screen. wrefresh works by first copying the named window
665          to  the  virtual  screen (wnoutrefresh()), and then calling the
666          routine  to  update  the screen (doupdate()). If the programmer
667          wishes  to output several windows at once, a series of calls to
668          wrefresh will result in alternating calls to wnoutrefresh() and
669          doupdate(),  causing several bursts of output to the screen. By
670          calling  wnoutrefresh() for each window, it is then possible to
671          call  doupdate()  once,  resulting in only one burst of output,
672          with  fewer  total  characters  transmitted (this also avoids a
673          visually annoying flicker at each update).
674
675  Low-Level Capability Access
676
677   setupterm(term, filenum, errret)
678          This  routine is called to initialize a terminal's description,
679          without setting up the curses screen structures or changing the
680          tty-driver mode bits. term is the character string representing
681          the  name  of the terminal being used. filenum is the UNIX file
682          descriptor  of  the terminal to be used for output. errret is a
683          pointer to an integer, in which a success or failure indication
684          is  returned. The values returned can be 1 (all is well), 0 (no
685          such  terminal),  or  -1  (some  problem  locating the terminfo
686          database).
687
688          The  value  of  term can be given as NULL, which will cause the
689          value of TERM in the environment to be used. The errret pointer
690          can  also be given as NULL, meaning no error code is wanted. If
691          errret is defaulted, and something goes wrong, setupterm() will
692          print  an  appropriate  error  message  and  exit,  rather than
693          returning.  Thus,  a simple program can call setupterm(0, 1, 0)
694          and not worry about initialization errors.
695
696          After  the call to setupterm(), the global variable cur_term is
697          set to point to the current structure of terminal capabilities.
698          By  calling  setupterm()  for  each  terminal,  and  saving and
699          restoring  cur_term, it is possible for a program to use two or
700          more  terminals  at  once.  Setupterm()  also  stores the names
701          section  of  the  terminal  description in the global character
702          array ttytype[]. Subsequent calls to setupterm() will overwrite
703          this array, so you'll have to save it yourself if need be.
704
705  Debugging
706
707     NOTE: These functions are not part of the standard curses API!
708
709   trace()
710          This  function  can be used to explicitly set a trace level. If
711          the  trace  level  is  nonzero,  execution of your program will
712          generate a file called `trace' in the current working directory
713          containing  a  report  on  the  library's actions. Higher trace
714          levels  enable  more  detailed  (and  verbose) reporting -- see
715          comments  attached  to  TRACE_ defines in the curses.h file for
716          details. (It is also possible to set a trace level by assigning
717          a trace level value to the environment variable NCURSES_TRACE).
718
719   _tracef()
720          This  function  can  be  used  to  output  your  own  debugging
721          information.  It  is  only  available  only  if  you  link with
722          -lncurses_g.  It  can be used the same way as printf(), only it
723          outputs  a  newline after the end of arguments. The output goes
724          to a file called trace in the current directory.
725
726   Trace  logs  can  be difficult to interpret due to the sheer volume of
727   data dumped in them. There is a script called tracemunch included with
728   the  ncurses distribution that can alleviate this problem somewhat; it
729   compacts  long  sequences  of  similar  operations  into more succinct
730   single-line  pseudo-operations.  These pseudo-ops can be distinguished
731   by the fact that they are named in capital letters.
732
733Hints, Tips, and Tricks
734
735   The ncurses manual pages are a complete reference for this library. In
736   the remainder of this document, we discuss various useful methods that
737   may not be obvious from the manual page descriptions.
738
739  Some Notes of Caution
740
741   If  you  find yourself thinking you need to use noraw() or nocbreak(),
742   think  again  and  move  carefully. It's probably better design to use
743   getstr()  or one of its relatives to simulate cooked mode. The noraw()
744   and  nocbreak() functions try to restore cooked mode, but they may end
745   up   clobbering   some  control  bits  set  before  you  started  your
746   application.  Also,  they  have always been poorly documented, and are
747   likely   to  hurt  your  application's  usability  with  other  curses
748   libraries.
749
750   Bear  in  mind that refresh() is a synonym for wrefresh(stdscr). Don't
751   try  to  mix use of stdscr with use of windows declared by newwin(); a
752   refresh()  call will blow them off the screen. The right way to handle
753   this  is  to  use  subwin(),  or not touch stdscr at all and tile your
754   screen  with  declared windows which you then wnoutrefresh() somewhere
755   in  your  program event loop, with a single doupdate() call to trigger
756   actual repainting.
757
758   You  are  much  less  likely  to  run into problems if you design your
759   screen   layouts   to  use  tiled  rather  than  overlapping  windows.
760   Historically,  curses  support  for overlapping windows has been weak,
761   fragile,  and  poorly  documented.  The  ncurses library is not yet an
762   exception to this rule.
763
764   There  is  a  panels library included in the ncurses distribution that
765   does  a  pretty  good  job  of  strengthening  the overlapping-windows
766   facilities.
767
768   Try to avoid using the global variables LINES and COLS. Use getmaxyx()
769   on  the stdscr context instead. Reason: your code may be ported to run
770   in  an  environment with window resizes, in which case several screens
771   could be open with different sizes.
772
773  Temporarily Leaving NCURSES Mode
774
775   Sometimes  you  will  want  to write a program that spends most of its
776   time  in  screen  mode,  but occasionally returns to ordinary `cooked'
777   mode.  A common reason for this is to support shell-out. This behavior
778   is simple to arrange in ncurses.
779
780   To  leave  ncurses  mode,  call  endwin()  as  you  would  if you were
781   intending  to terminate the program. This will take the screen back to
782   cooked  mode;  you  can  do your shell-out. When you want to return to
783   ncurses  mode,  simply call refresh() or doupdate(). This will repaint
784   the screen.
785
786   There  is  a  boolean function, isendwin(), which code can use to test
787   whether ncurses screen mode is active. It returns TRUE in the interval
788   between an endwin() call and the following refresh(), FALSE otherwise.
789
790   Here is some sample code for shellout:
791    addstr("Shelling out...");
792    def_prog_mode();           /* save current tty modes */
793    endwin();                  /* restore original tty modes */
794    system("sh");              /* run shell */
795    addstr("returned.\n");     /* prepare return message */
796    refresh();                 /* restore save modes, repaint screen */
797
798  Using NCURSES under XTERM
799
800   A  resize  operation  in  X  sends SIGWINCH to the application running
801   under  xterm.  The  easiest way to handle SIGWINCH is to do an endwin,
802   followed  by  an  refresh  and a screen repaint you code yourself. The
803   refresh will pick up the new screen size from the xterm's environment.
804
805   That  is the standard way, of course (it even works with some vendor's
806   curses  implementations). Its drawback is that it clears the screen to
807   reinitialize the display, and does not resize subwindows which must be
808   shrunk.   Ncurses  provides  an  extension  which  works  better,  the
809   resizeterm  function.  That  function  ensures  that  all  windows are
810   limited  to  the new screen dimensions, and pads stdscr with blanks if
811   the screen is larger.
812
813   The ncurses library provides a SIGWINCH signal handler, which pushes a
814   KEY_RESIZE  via the wgetch() calls. When ncurses returns that code, it
815   calls  resizeterm  to update the size of the standard screen's window,
816   repainting that (filling with blanks or truncating as needed). It also
817   resizes other windows, but its effect may be less satisfactory because
818   it  cannot  know  how you want the screen re-painted. You will usually
819   have to write special-purpose code to handle KEY_RESIZE yourself.
820
821  Handling Multiple Terminal Screens
822
823   The initscr() function actually calls a function named newterm() to do
824   most  of  its  work.  If you are writing a program that opens multiple
825   terminals, use newterm() directly.
826
827   For  each call, you will have to specify a terminal type and a pair of
828   file  pointers;  each  call will return a screen reference, and stdscr
829   will be set to the last one allocated. You will switch between screens
830   with  the  set_term  call.  Note  that  you  will  also  have  to call
831   def_shell_mode and def_prog_mode on each tty yourself.
832
833  Testing for Terminal Capabilities
834
835   Sometimes you may want to write programs that test for the presence of
836   various  capabilities before deciding whether to go into ncurses mode.
837   An  easy way to do this is to call setupterm(), then use the functions
838   tigetflag(), tigetnum(), and tigetstr() to do your testing.
839
840   A  particularly  useful  case  of this often comes up when you want to
841   test  whether  a  given  terminal  type  should  be treated as `smart'
842   (cursor-addressable) or `stupid'. The right way to test this is to see
843   if the return value of tigetstr("cup") is non-NULL. Alternatively, you
844   can  include  the  term.h  file  and  test  the  value  of  the  macro
845   cursor_address.
846
847  Tuning for Speed
848
849   Use  the  addchstr()  family  of functions for fast screen-painting of
850   text  when  you  know the text doesn't contain any control characters.
851   Try  to  make  attribute changes infrequent on your screens. Don't use
852   the immedok() option!
853
854  Special Features of NCURSES
855
856   The  wresize()  function  allows  you to resize a window in place. The
857   associated   resizeterm()  function  simplifies  the  construction  of
858   SIGWINCH handlers, for resizing all windows.
859
860   The define_key() function allows you to define at runtime function-key
861   control  sequences  which  are  not  in  the terminal description. The
862   keyok()   function   allows  you  to  temporarily  enable  or  disable
863   interpretation of any function-key control sequence.
864
865   The use_default_colors() function allows you to construct applications
866   which  can use the terminal's default foreground and background colors
867   as  an  additional "default" color. Several terminal emulators support
868   this feature, which is based on ISO 6429.
869
870   Ncurses  supports  up 16 colors, unlike SVr4 curses which defines only
871   8. While most terminals which provide color allow only 8 colors, about
872   a quarter (including XFree86 xterm) support 16 colors.
873
874Compatibility with Older Versions
875
876   Despite  our  best efforts, there are some differences between ncurses
877   and  the  (undocumented!)  behavior  of  older curses implementations.
878   These  arise from ambiguities or omissions in the documentation of the
879   API.
880
881  Refresh of Overlapping Windows
882
883   If  you  define two windows A and B that overlap, and then alternately
884   scribble  on  and  refresh  them,  the changes made to the overlapping
885   region  under  historic  curses  versions  were  often  not documented
886   precisely.
887
888   To  understand why this is a problem, remember that screen updates are
889   calculated  between  two  representations  of  the entire display. The
890   documentation  says that when you refresh a window, it is first copied
891   to  the  virtual screen, and then changes are calculated to update the
892   physical  screen (and applied to the terminal). But "copied to" is not
893   very specific, and subtle differences in how copying works can produce
894   different behaviors in the case where two overlapping windows are each
895   being refreshed at unpredictable intervals.
896
897   What  happens to the overlapping region depends on what wnoutrefresh()
898   does  with  its  argument  --  what portions of the argument window it
899   copies  to  the virtual screen. Some implementations do "change copy",
900   copying  down  only locations in the window that have changed (or been
901   marked  changed  with wtouchln() and friends). Some implementations do
902   "entire  copy",  copying  all  window  locations to the virtual screen
903   whether or not they have changed.
904
905   The  ncurses  library  itself  has  not always been consistent on this
906   score.  Due  to  a  bug,  versions  1.8.7  to  1.9.8a did entire copy.
907   Versions  1.8.6  and  older,  and  versions 1.9.9 and newer, do change
908   copy.
909
910   For  most  commercial curses implementations, it is not documented and
911   not  known  for sure (at least not to the ncurses maintainers) whether
912   they  do  change  copy or entire copy. We know that System V release 3
913   curses  has  logic in it that looks like an attempt to do change copy,
914   but  the  surrounding  logic and data representations are sufficiently
915   complex,  and  our  knowledge sufficiently indirect, that it's hard to
916   know  whether  this  is  reliable.  It  is  not  clear  what  the SVr4
917   documentation  and XSI standard intend. The XSI Curses standard barely
918   mentions  wnoutrefresh();  the  SVr4  documents  seem to be describing
919   entire-copy, but it is possible with some effort and straining to read
920   them the other way.
921
922   It  might  therefore  be unwise to rely on either behavior in programs
923   that  might  have  to  be  linked  with  other curses implementations.
924   Instead,  you  can do an explicit touchwin() before the wnoutrefresh()
925   call to guarantee an entire-contents copy anywhere.
926
927   The  really clean way to handle this is to use the panels library. If,
928   when  you want a screen update, you do update_panels(), it will do all
929   the  necessary  wnoutrefresh() calls for whatever panel stacking order
930   you  have  defined. Then you can do one doupdate() and there will be a
931   single burst of physical I/O that will do all your updates.
932
933  Background Erase
934
935   If you have been using a very old versions of ncurses (1.8.7 or older)
936   you  may be surprised by the behavior of the erase functions. In older
937   versions,  erased  areas of a window were filled with a blank modified
938   by  the  window's  current attribute (as set by wattrset(), wattron(),
939   wattroff() and friends).
940
941   In  newer  versions,  this is not so. Instead, the attribute of erased
942   blanks  is  normal  unless  and  until it is modified by the functions
943   bkgdset() or wbkgdset().
944
945   This change in behavior conforms ncurses to System V Release 4 and the
946   XSI Curses standard.
947
948XSI Curses Conformance
949
950   The  ncurses  library is intended to be base-level conformant with the
951   XSI  Curses  standard  from  X/Open.  Many extended-level features (in
952   fact,  almost all features not directly concerned with wide characters
953   and internationalization) are also supported.
954
955   One  effect  of  XSI  conformance  is the change in behavior described
956   under "Background Erase -- Compatibility with Old Versions".
957
958   Also,  ncurses  meets the XSI requirement that every macro entry point
959   have  a  corresponding  function  which  may  be  linked  (and will be
960   prototype-checked) if the macro definition is disabled with #undef.
961
962                              The Panels Library
963
964   The  ncurses  library  by  itself  provides  good  support  for screen
965   displays in which the windows are tiled (non-overlapping). In the more
966   general  case  that  windows  may overlap, you have to use a series of
967   wnoutrefresh()  calls  followed  by a doupdate(), and be careful about
968   the order you do the window refreshes in. It has to be bottom-upwards,
969   otherwise parts of windows that should be obscured will show through.
970
971   When  your  interface design is such that windows may dive deeper into
972   the  visibility  stack  or  pop  to  the top at runtime, the resulting
973   book-keeping  can  be  tedious  and  difficult to get right. Hence the
974   panels library.
975
976   The  panel  library  first  appeared  in  AT&T  System  V. The version
977   documented here is the panel code distributed with ncurses.
978
979Compiling With the Panels Library
980
981   Your  panels-using modules must import the panels library declarations
982   with
983          #include <panel.h>
984
985   and must be linked explicitly with the panels library using an -lpanel
986   argument.  Note  that  they  must  also  link the ncurses library with
987   -lncurses. Many linkers are two-pass and will accept either order, but
988   it is still good practice to put -lpanel first and -lncurses second.
989
990Overview of Panels
991
992   A  panel  object  is  a window that is implicitly treated as part of a
993   deck  including  all  other  panel  objects.  The deck has an implicit
994   bottom-to-top  visibility order. The panels library includes an update
995   function (analogous to refresh()) that displays all panels in the deck
996   in  the proper order to resolve overlaps. The standard window, stdscr,
997   is considered below all panels.
998
999   Details  on the panels functions are available in the man pages. We'll
1000   just hit the highlights here.
1001
1002   You  create  a  panel from a window by calling new_panel() on a window
1003   pointer.  It  then  becomes the top of the deck. The panel's window is
1004   available as the value of panel_window() called with the panel pointer
1005   as argument.
1006
1007   You  can  delete  a  panel (removing it from the deck) with del_panel.
1008   This  will  not  deallocate the associated window; you have to do that
1009   yourself.  You can replace a panel's window with a different window by
1010   calling  replace_window.  The new window may be of different size; the
1011   panel code will re-compute all overlaps. This operation doesn't change
1012   the panel's position in the deck.
1013
1014   To  move  a  panel's window, use move_panel(). The mvwin() function on
1015   the  panel's  window  isn't  sufficient  because it doesn't update the
1016   panels  library's  representation  of  where  the  windows  are.  This
1017   operation leaves the panel's depth, contents, and size unchanged.
1018
1019   Two   functions   (top_panel(),   bottom_panel())   are  provided  for
1020   rearranging the deck. The first pops its argument window to the top of
1021   the  deck;  the second sends it to the bottom. Either operation leaves
1022   the panel's screen location, contents, and size unchanged.
1023
1024   The  function update_panels() does all the wnoutrefresh() calls needed
1025   to prepare for doupdate() (which you must call yourself, afterwards).
1026
1027   Typically,  you  will want to call update_panels() and doupdate() just
1028   before accepting command input, once in each cycle of interaction with
1029   the  user.  If  you  call  update_panels()  after each and every panel
1030   write,  you'll  generate  a  lot  of  unnecessary refresh activity and
1031   screen flicker.
1032
1033Panels, Input, and the Standard Screen
1034
1035   You  shouldn't mix wnoutrefresh() or wrefresh() operations with panels
1036   code;  this will work only if the argument window is either in the top
1037   panel or unobscured by any other panels.
1038
1039   The  stsdcr  window  is  a  special  case.  It is considered below all
1040   panels. Because changes to panels may obscure parts of stdscr, though,
1041   you  should  call update_panels() before doupdate() even when you only
1042   change stdscr.
1043
1044   Note  that  wgetch  automatically  calls  wrefresh.  Therefore, before
1045   requesting  input  from  a  panel window, you need to be sure that the
1046   panel is totally unobscured.
1047
1048   There  is  presently  no  way to display changes to one obscured panel
1049   without repainting all panels.
1050
1051Hiding Panels
1052
1053   It's  possible  to  remove  a  panel  from  the  deck temporarily; use
1054   hide_panel  for this. Use show_panel() to render it visible again. The
1055   predicate  function  panel_hidden  tests  whether  or  not  a panel is
1056   hidden.
1057
1058   The panel_update code ignores hidden panels. You cannot do top_panel()
1059   or  bottom_panel  on  a  hidden  panel().  Other panels operations are
1060   applicable.
1061
1062Miscellaneous Other Facilities
1063
1064   It's  possible  to navigate the deck using the functions panel_above()
1065   and  panel_below.  Handed a panel pointer, they return the panel above
1066   or  below  that  panel.  Handed  NULL,  they return the bottom-most or
1067   top-most panel.
1068
1069   Every  panel  has  an  associated  user pointer, not used by the panel
1070   code,  to  which  you  can  attach  application data. See the man page
1071   documentation of set_panel_userptr() and panel_userptr for details.
1072
1073                               The Menu Library
1074
1075   A menu is a screen display that assists the user to choose some subset
1076   of  a  given set of items. The menu library is a curses extension that
1077   supports  easy  programming  of  menu  hierarchies  with a uniform but
1078   flexible interface.
1079
1080   The  menu  library  first  appeared  in  AT&T  System  V.  The version
1081   documented here is the menu code distributed with ncurses.
1082
1083Compiling With the menu Library
1084
1085   Your menu-using modules must import the menu library declarations with
1086          #include <menu.h>
1087
1088   and  must  be linked explicitly with the menus library using an -lmenu
1089   argument.  Note  that  they  must  also  link the ncurses library with
1090   -lncurses. Many linkers are two-pass and will accept either order, but
1091   it is still good practice to put -lmenu first and -lncurses second.
1092
1093Overview of Menus
1094
1095   The  menus  created  by  this  library consist of collections of items
1096   including  a  name  string part and a description string part. To make
1097   menus,  you  create  groups  of these items and connect them with menu
1098   frame objects.
1099
1100   The  menu can then by posted, that is written to an associated window.
1101   Actually, each menu has two associated windows; a containing window in
1102   which  the  programmer can scribble titles or borders, and a subwindow
1103   in which the menu items proper are displayed. If this subwindow is too
1104   small  to  display  all the items, it will be a scrollable viewport on
1105   the collection of items.
1106
1107   A  menu may also be unposted (that is, undisplayed), and finally freed
1108   to  make  the  storage  associated with it and its items available for
1109   re-use.
1110
1111   The general flow of control of a menu program looks like this:
1112    1. Initialize curses.
1113    2. Create the menu items, using new_item().
1114    3. Create the menu using new_menu().
1115    4. Post the menu using post_menu().
1116    5. Refresh the screen.
1117    6. Process user requests via an input loop.
1118    7. Unpost the menu using unpost_menu().
1119    8. Free the menu, using free_menu().
1120    9. Free the items using free_item().
1121   10. Terminate curses.
1122
1123Selecting items
1124
1125   Menus  may  be  multi-valued  or  (the default) single-valued (see the
1126   manual  page  menu_opts(3x)  to  see  how to change the default). Both
1127   types always have a current item.
1128
1129   From  a  single-valued  menu you can read the selected value simply by
1130   looking  at  the  current  item. From a multi-valued menu, you get the
1131   selected  set  by  looping through the items applying the item_value()
1132   predicate  function.  Your  menu-processing  code can use the function
1133   set_item_value() to flag the items in the select set.
1134
1135   Menu   items   can  be  made  unselectable  using  set_item_opts()  or
1136   item_opts_off()  with  the  O_SELECTABLE  argument.  This  is the only
1137   option  so  far  defined for menus, but it is good practice to code as
1138   though other option bits might be on.
1139
1140Menu Display
1141
1142   The  menu  library  calculates a minimum display size for your window,
1143   based on the following variables:
1144     * The number and maximum length of the menu items
1145     * Whether the O_ROWMAJOR option is enabled
1146     * Whether display of descriptions is enabled
1147     * Whatever menu format may have been set by the programmer
1148     * The  length of the menu mark string used for highlighting selected
1149       items
1150
1151   The  function  set_menu_format() allows you to set the maximum size of
1152   the viewport or menu page that will be used to display menu items. You
1153   can retrieve any format associated with a menu with menu_format(). The
1154   default format is rows=16, columns=1.
1155
1156   The actual menu page may be smaller than the format size. This depends
1157   on  the item number and size and whether O_ROWMAJOR is on. This option
1158   (on  by  default) causes menu items to be displayed in a `raster-scan'
1159   pattern, so that if more than one item will fit horizontally the first
1160   couple  of  items  are side-by-side in the top row. The alternative is
1161   column-major  display,  which  tries to put the first several items in
1162   the first column.
1163
1164   As  mentioned above, a menu format not large enough to allow all items
1165   to  fit  on-screen  will  result  in a menu display that is vertically
1166   scrollable.
1167
1168   You  can  scroll  it  with  requests to the menu driver, which will be
1169   described in the section on menu input handling.
1170
1171   Each  menu  has a mark string used to visually tag selected items; see
1172   the menu_mark(3x) manual page for details. The mark string length also
1173   influences the menu page size.
1174
1175   The  function  scale_menu()  returns the minimum display size that the
1176   menu  code  computes  from  all  these  factors.  There are other menu
1177   display  attributes  including  a  select  attribute, an attribute for
1178   selectable  items,  an  attribute  for  unselectable  items, and a pad
1179   character used to separate item name text from description text. These
1180   have  reasonable  defaults which the library allows you to change (see
1181   the menu_attribs(3x) manual page.
1182
1183Menu Windows
1184
1185   Each  menu has, as mentioned previously, a pair of associated windows.
1186   Both these windows are painted when the menu is posted and erased when
1187   the menu is unposted.
1188
1189   The  outer  or  frame  window  is  not  otherwise  touched by the menu
1190   routines. It exists so the programmer can associate a title, a border,
1191   or  perhaps  help text with the menu and have it properly refreshed or
1192   erased at post/unpost time. The inner window or subwindow is where the
1193   current menu page is displayed.
1194
1195   By  default,  both  windows  are  stdscr.  You  can  set them with the
1196   functions in menu_win(3x).
1197
1198   When  you  call post_menu(), you write the menu to its subwindow. When
1199   you  call  unpost_menu(), you erase the subwindow, However, neither of
1200   these  actually  modifies  the  screen. To do that, call wrefresh() or
1201   some equivalent.
1202
1203Processing Menu Input
1204
1205   The  main  loop of your menu-processing code should call menu_driver()
1206   repeatedly.  The first argument of this routine is a menu pointer; the
1207   second  is  a  menu  command  code. You should write an input-fetching
1208   routine that maps input characters to menu command codes, and pass its
1209   output  to  menu_driver(). The menu command codes are fully documented
1210   in menu_driver(3x).
1211
1212   The  simplest  group of command codes is REQ_NEXT_ITEM, REQ_PREV_ITEM,
1213   REQ_FIRST_ITEM,     REQ_LAST_ITEM,     REQ_UP_ITEM,     REQ_DOWN_ITEM,
1214   REQ_LEFT_ITEM,  REQ_RIGHT_ITEM.  These  change  the currently selected
1215   item.  These  requests may cause scrolling of the menu page if it only
1216   partially displayed.
1217
1218   There  are  explicit  requests  for  scrolling  which  also change the
1219   current  item  (because  the  select location does not change, but the
1220   item    there   does).   These   are   REQ_SCR_DLINE,   REQ_SCR_ULINE,
1221   REQ_SCR_DPAGE, and REQ_SCR_UPAGE.
1222
1223   The  REQ_TOGGLE_ITEM  selects or deselects the current item. It is for
1224   use  in  multi-valued  menus; if you use it with O_ONEVALUE on, you'll
1225   get an error return (E_REQUEST_DENIED).
1226
1227   Each  menu  has  an associated pattern buffer. The menu_driver() logic
1228   tries  to  accumulate  printable  ASCII  characters  passed in in that
1229   buffer;  when  it  matches a prefix of an item name, that item (or the
1230   next  matching  item)  is selected. If appending a character yields no
1231   new  match,  that  character  is  deleted from the pattern buffer, and
1232   menu_driver() returns E_NO_MATCH.
1233
1234   Some  requests  change the pattern buffer directly: REQ_CLEAR_PATTERN,
1235   REQ_BACK_PATTERN,  REQ_NEXT_MATCH,  REQ_PREV_MATCH. The latter two are
1236   useful  when  pattern  buffer  input  matches  more than one item in a
1237   multi-valued menu.
1238
1239   Each  successful  scroll or item navigation request clears the pattern
1240   buffer.  It is also possible to set the pattern buffer explicitly with
1241   set_menu_pattern().
1242
1243   Finally,  menu  driver  requests  above  the  constant MAX_COMMAND are
1244   considered   application-specific  commands.  The  menu_driver()  code
1245   ignores them and returns E_UNKNOWN_COMMAND.
1246
1247Miscellaneous Other Features
1248
1249   Various  menu  options can affect the processing and visual appearance
1250   and input processing of menus. See menu_opts(3x) for details.
1251
1252   It  is possible to change the current item from application code; this
1253   is  useful  if  you  want to write your own navigation requests. It is
1254   also  possible  to explicitly set the top row of the menu display. See
1255   mitem_current(3x).  If  your  application  needs  to  change  the menu
1256   subwindow  cursor for any reason, pos_menu_cursor() will restore it to
1257   the correct location for continuing menu driver processing.
1258
1259   It  is  possible  to set hooks to be called at menu initialization and
1260   wrapup   time,   and   whenever   the   selected   item  changes.  See
1261   menu_hook(3x).
1262
1263   Each  item, and each menu, has an associated user pointer on which you
1264   can hang application data. See mitem_userptr(3x) and menu_userptr(3x).
1265
1266                               The Forms Library
1267
1268   The  form library is a curses extension that supports easy programming
1269   of on-screen forms for data entry and program control.
1270
1271   The  form  library  first  appeared  in  AT&T  System  V.  The version
1272   documented here is the form code distributed with ncurses.
1273
1274Compiling With the form Library
1275
1276   Your form-using modules must import the form library declarations with
1277          #include <form.h>
1278
1279   and  must  be linked explicitly with the forms library using an -lform
1280   argument.  Note  that  they  must  also  link the ncurses library with
1281   -lncurses. Many linkers are two-pass and will accept either order, but
1282   it is still good practice to put -lform first and -lncurses second.
1283
1284Overview of Forms
1285
1286   A  form  is  a  collection of fields; each field may be either a label
1287   (explanatory  text)  or  a  data-entry  location.  Long  forms  may be
1288   segmented into pages; each entry to a new page clears the screen.
1289
1290   To  make forms, you create groups of fields and connect them with form
1291   frame objects; the form library makes this relatively simple.
1292
1293   Once  defined,  a form can be posted, that is written to an associated
1294   window.  Actually,  each form has two associated windows; a containing
1295   window  in  which the programmer can scribble titles or borders, and a
1296   subwindow in which the form fields proper are displayed.
1297
1298   As  the  form  user  fills out the posted form, navigation and editing
1299   keys  support  movement between fields, editing keys support modifying
1300   field,  and plain text adds to or changes data in a current field. The
1301   form  library  allows you (the forms designer) to bind each navigation
1302   and  editing  key  to any keystroke accepted by curses Fields may have
1303   validation  conditions on them, so that they check input data for type
1304   and  value.  The form library supplies a rich set of pre-defined field
1305   types, and makes it relatively easy to define new ones.
1306
1307   Once its transaction is completed (or aborted), a form may be unposted
1308   (that  is,  undisplayed),  and  finally  freed  to  make  the  storage
1309   associated with it and its items available for re-use.
1310
1311   The general flow of control of a form program looks like this:
1312    1. Initialize curses.
1313    2. Create the form fields, using new_field().
1314    3. Create the form using new_form().
1315    4. Post the form using post_form().
1316    5. Refresh the screen.
1317    6. Process user requests via an input loop.
1318    7. Unpost the form using unpost_form().
1319    8. Free the form, using free_form().
1320    9. Free the fields using free_field().
1321   10. Terminate curses.
1322
1323   Note  that  this  looks  much  like  a  menu program; the form library
1324   handles  tasks  which  are in many ways similar, and its interface was
1325   obviously  designed  to  resemble  that  of  the menu library wherever
1326   possible.
1327
1328   In  forms  programs,  however, the `process user requests' is somewhat
1329   more   complicated   than  for  menus.  Besides  menu-like  navigation
1330   operations, the menu driver loop has to support field editing and data
1331   validation.
1332
1333Creating and Freeing Fields and Forms
1334
1335   The basic function for creating fields is new_field():
1336FIELD *new_field(int height, int width,   /* new field size */
1337                 int top, int left,       /* upper left corner */
1338                 int offscreen,           /* number of offscreen rows */
1339                 int nbuf);               /* number of working buffers */
1340
1341   Menu  items  always  occupy  a  single  row, but forms fields may have
1342   multiple  rows.  So  new_field()  requires  you to specify a width and
1343   height  (the  first  two  arguments,  which  mist both be greater than
1344   zero).
1345
1346   You must also specify the location of the field's upper left corner on
1347   the  screen  (the  third  and  fourth arguments, which must be zero or
1348   greater).  Note  that  these  coordinates  are  relative  to  the form
1349   subwindow,  which will coincide with stdscr by default but need not be
1350   stdscr if you've done an explicit set_form_win() call.
1351
1352   The  fifth argument allows you to specify a number of off-screen rows.
1353   If  this  is zero, the entire field will always be displayed. If it is
1354   nonzero,  the  form  will  be  scrollable,  with  only one screen-full
1355   (initially  the  top  part) displayed at any given time. If you make a
1356   field  dynamic and grow it so it will no longer fit on the screen, the
1357   form  will  become  scrollable  even  if  the  offscreen  argument was
1358   initially zero.
1359
1360   The  forms library allocates one working buffer per field; the size of
1361   each buffer is ((height + offscreen)*width + 1, one character for each
1362   position in the field plus a NUL terminator. The sixth argument is the
1363   number  of  additional  data  buffers  to allocate for the field; your
1364   application can use them for its own purposes.
1365FIELD *dup_field(FIELD *field,            /* field to copy */
1366                 int top, int left);      /* location of new copy */
1367
1368   The  function  dup_field()  duplicates  an  existing  field  at  a new
1369   location.  Size  and  buffering information are copied; some attribute
1370   flags  and  status  bits  are  not  (see  the  form_field_new(3X)  for
1371   details).
1372FIELD *link_field(FIELD *field,           /* field to copy */
1373                  int top, int left);     /* location of new copy */
1374
1375   The  function  link_field() also duplicates an existing field at a new
1376   location.  The difference from dup_field() is that it arranges for the
1377   new field's buffer to be shared with the old one.
1378
1379   Besides  the obvious use in making a field editable from two different
1380   form pages, linked fields give you a way to hack in dynamic labels. If
1381   you  declare  several fields linked to an original, and then make them
1382   inactive,  changes  from  the original will still be propagated to the
1383   linked fields.
1384
1385   As  with duplicated fields, linked fields have attribute bits separate
1386   from the original.
1387
1388   As  you  might  guess,  all these field-allocations return NULL if the
1389   field  allocation  is  not  possible  due to an out-of-memory error or
1390   out-of-bounds arguments.
1391
1392   To connect fields to a form, use
1393FORM *new_form(FIELD **fields);
1394
1395   This  function  expects  to  see  a  NULL-terminated  array  of  field
1396   pointers.  Said fields are connected to a newly-allocated form object;
1397   its address is returned (or else NULL if the allocation fails).
1398
1399   Note  that  new_field()  does  not copy the pointer array into private
1400   storage;  if you modify the contents of the pointer array during forms
1401   processing,  all manner of bizarre things might happen. Also note that
1402   any given field may only be connected to one form.
1403
1404   The  functions  free_field() and free_form are available to free field
1405   and  form objects. It is an error to attempt to free a field connected
1406   to a form, but not vice-versa; thus, you will generally free your form
1407   objects first.
1408
1409Fetching and Changing Field Attributes
1410
1411   Each  form  field  has  a  number  of  location  and  size  attributes
1412   associated  with  it. There are other field attributes used to control
1413   display and editing of the field. Some (for example, the O_STATIC bit)
1414   involve  sufficient  complications  to be covered in sections of their
1415   own later on. We cover the functions used to get and set several basic
1416   attributes here.
1417
1418   When a field is created, the attributes not specified by the new_field
1419   function  are  copied  from  an  invisible  system  default  field. In
1420   attribute-setting  and -fetching functions, the argument NULL is taken
1421   to mean this field. Changes to it persist as defaults until your forms
1422   application terminates.
1423
1424  Fetching Size and Location Data
1425
1426   You can retrieve field sizes and locations through:
1427int field_info(FIELD *field,              /* field from which to fetch */
1428               int *height, *int width,   /* field size */
1429               int *top, int *left,       /* upper left corner */
1430               int *offscreen,            /* number of offscreen rows */
1431               int *nbuf);                /* number of working buffers */
1432
1433   This  function is a sort of inverse of new_field(); instead of setting
1434   size  and  location attributes of a new field, it fetches them from an
1435   existing one.
1436
1437  Changing the Field Location
1438
1439   It is possible to move a field's location on the screen:
1440int move_field(FIELD *field,              /* field to alter */
1441               int top, int left);        /* new upper-left corner */
1442
1443   You can, of course. query the current location through field_info().
1444
1445  The Justification Attribute
1446
1447   One-line  fields  may be unjustified, justified right, justified left,
1448   or centered. Here is how you manipulate this attribute:
1449int set_field_just(FIELD *field,          /* field to alter */
1450                   int justmode);         /* mode to set */
1451
1452int field_just(FIELD *field);             /* fetch mode of field */
1453
1454   The   mode   values  accepted  and  returned  by  this  functions  are
1455   preprocessor  macros NO_JUSTIFICATION, JUSTIFY_RIGHT, JUSTIFY_LEFT, or
1456   JUSTIFY_CENTER.
1457
1458  Field Display Attributes
1459
1460   For  each  field,  you  can  set  a  foreground  attribute for entered
1461   characters,  a  background  attribute  for the entire field, and a pad
1462   character  for the unfilled portion of the field. You can also control
1463   pagination of the form.
1464
1465   This  group of four field attributes controls the visual appearance of
1466   the  field on the screen, without affecting in any way the data in the
1467   field buffer.
1468int set_field_fore(FIELD *field,          /* field to alter */
1469                   chtype attr);          /* attribute to set */
1470
1471chtype field_fore(FIELD *field);          /* field to query */
1472
1473int set_field_back(FIELD *field,          /* field to alter */
1474                   chtype attr);          /* attribute to set */
1475
1476chtype field_back(FIELD *field);          /* field to query */
1477
1478int set_field_pad(FIELD *field,           /* field to alter */
1479                 int pad);                /* pad character to set */
1480
1481chtype field_pad(FIELD *field);
1482
1483int set_new_page(FIELD *field,            /* field to alter */
1484                 int flag);               /* TRUE to force new page */
1485
1486chtype new_page(FIELD *field);            /* field to query */
1487
1488   The attributes set and returned by the first four functions are normal
1489   curses(3x)  display  attribute  values  (A_STANDOUT, A_BOLD, A_REVERSE
1490   etc).  The page bit of a field controls whether it is displayed at the
1491   start of a new form screen.
1492
1493  Field Option Bits
1494
1495   There  is  also a large collection of field option bits you can set to
1496   control  various  aspects of forms processing. You can manipulate them
1497   with these functions:
1498int set_field_opts(FIELD *field,          /* field to alter */
1499                   int attr);             /* attribute to set */
1500
1501int field_opts_on(FIELD *field,           /* field to alter */
1502                  int attr);              /* attributes to turn on */
1503
1504int field_opts_off(FIELD *field,          /* field to alter */
1505                   int attr);             /* attributes to turn off */
1506
1507int field_opts(FIELD *field);             /* field to query */
1508
1509   By default, all options are on. Here are the available option bits:
1510
1511   O_VISIBLE
1512          Controls  whether  the  field  is visible on the screen. Can be
1513          used  during form processing to hide or pop up fields depending
1514          on the value of parent fields.
1515
1516   O_ACTIVE
1517          Controls  whether  the  field is active during forms processing
1518          (i.e.  visited  by  form  navigation keys). Can be used to make
1519          labels  or  derived  fields with buffer values alterable by the
1520          forms application, not the user.
1521
1522   O_PUBLIC
1523          Controls  whether data is displayed during field entry. If this
1524          option  is  turned  off on a field, the library will accept and
1525          edit  data  in that field, but it will not be displayed and the
1526          visible  field  cursor  will  not  move.  You  can turn off the
1527          O_PUBLIC bit to define password fields.
1528
1529   O_EDIT
1530          Controls  whether  the  field's data can be modified. When this
1531          option  is off, all editing requests except REQ_PREV_CHOICE and
1532          REQ_NEXT_CHOICE  will fail. Such read-only fields may be useful
1533          for help messages.
1534
1535   O_WRAP
1536          Controls word-wrapping in multi-line fields. Normally, when any
1537          character  of  a  (blank-separated) word reaches the end of the
1538          current  line,  the  entire  word  is  wrapped to the next line
1539          (assuming there is one). When this option is off, the word will
1540          be split across the line break.
1541
1542   O_BLANK
1543          Controls  field  blanking.  When  this option is on, entering a
1544          character  at  the first field position erases the entire field
1545          (except for the just-entered character).
1546
1547   O_AUTOSKIP
1548          Controls  automatic  skip  to  next  field when this one fills.
1549          Normally,  when  the  forms user tries to type more data into a
1550          field  than will fit, the editing location jumps to next field.
1551          When this option is off, the user's cursor will hang at the end
1552          of  the  field.  This  option is ignored in dynamic fields that
1553          have not reached their size limit.
1554
1555   O_NULLOK
1556          Controls   whether  validation  is  applied  to  blank  fields.
1557          Normally,  it  is not; the user can leave a field blank without
1558          invoking  the usual validation check on exit. If this option is
1559          off on a field, exit from it will invoke a validation check.
1560
1561   O_PASSOK
1562          Controls whether validation occurs on every exit, or only after
1563          the  field  is  modified.  Normally the latter is true. Setting
1564          O_PASSOK  may be useful if your field's validation function may
1565          change during forms processing.
1566
1567   O_STATIC
1568          Controls  whether the field is fixed to its initial dimensions.
1569          If  you  turn  this  off,  the  field  becomes dynamic and will
1570          stretch to fit entered data.
1571
1572   A  field's  options  cannot  be  changed  while the field is currently
1573   selected.  However,  options  may be changed on posted fields that are
1574   not current.
1575
1576   The option values are bit-masks and can be composed with logical-or in
1577   the obvious way.
1578
1579Field Status
1580
1581   Every field has a status flag, which is set to FALSE when the field is
1582   created  and  TRUE when the value in field buffer 0 changes. This flag
1583   can be queried and set directly:
1584int set_field_status(FIELD *field,      /* field to alter */
1585                   int status);         /* mode to set */
1586
1587int field_status(FIELD *field);         /* fetch mode of field */
1588
1589   Setting  this  flag under program control can be useful if you use the
1590   same form repeatedly, looking for modified fields each time.
1591
1592   Calling  field_status()  on  a  field not currently selected for input
1593   will return a correct value. Calling field_status() on a field that is
1594   currently  selected for input may not necessarily give a correct field
1595   status  value, because entered data isn't necessarily copied to buffer
1596   zero  before the exit validation check. To guarantee that the returned
1597   status  value  reflects reality, call field_status() either (1) in the
1598   field's  exit validation check routine, (2) from the field's or form's
1599   initialization   or   termination   hooks,   or   (3)   just  after  a
1600   REQ_VALIDATION request has been processed by the forms driver.
1601
1602Field User Pointer
1603
1604   Each  field  structure contains one character pointer slot that is not
1605   used  by  the forms library. It is intended to be used by applications
1606   to store private per-field data. You can manipulate it with:
1607int set_field_userptr(FIELD *field,       /* field to alter */
1608                   char *userptr);        /* mode to set */
1609
1610char *field_userptr(FIELD *field);        /* fetch mode of field */
1611
1612   (Properly,  this  user  pointer field ought to have (void *) type. The
1613   (char *) type is retained for System V compatibility.)
1614
1615   It  is  valid  to  set  the  user pointer of the default field (with a
1616   set_field_userptr()  call  passed  a  NULL  field pointer.) When a new
1617   field  is  created,  the  default-field  user  pointer  is  copied  to
1618   initialize the new field's user pointer.
1619
1620Variable-Sized Fields
1621
1622   Normally,  a  field  is fixed at the size specified for it at creation
1623   time.  If,  however, you turn off its O_STATIC bit, it becomes dynamic
1624   and  will  automatically  resize  itself  to accommodate data as it is
1625   entered.  If the field has extra buffers associated with it, they will
1626   grow right along with the main input buffer.
1627
1628   A  one-line  dynamic  field  will have a fixed height (1) but variable
1629   width, scrolling horizontally to display data within the field area as
1630   originally  dimensioned  and  located. A multi-line dynamic field will
1631   have  a  fixed  width, but variable height (number of rows), scrolling
1632   vertically  to  display  data  within  the  field  area  as originally
1633   dimensioned and located.
1634
1635   Normally,  a dynamic field is allowed to grow without limit. But it is
1636   possible  to set an upper limit on the size of a dynamic field. You do
1637   it with this function:
1638int set_max_field(FIELD *field,     /* field to alter (may not be NULL) */
1639                   int max_size);   /* upper limit on field size */
1640
1641   If the field is one-line, max_size is taken to be a column size limit;
1642   if  it  is multi-line, it is taken to be a line size limit. To disable
1643   any  limit,  use  an argument of zero. The growth limit can be changed
1644   whether or not the O_STATIC bit is on, but has no effect until it is.
1645
1646   The following properties of a field change when it becomes dynamic:
1647     * If  there  is  no  growth limit, there is no final position of the
1648       field; therefore O_AUTOSKIP and O_NL_OVERLOAD are ignored.
1649     * Field justification will be ignored (though whatever justification
1650       is set up will be retained internally and can be queried).
1651     * The  dup_field() and link_field() calls copy dynamic-buffer sizes.
1652       If  the  O_STATIC  option  is set on one of a collection of links,
1653       buffer  resizing  will occur only when the field is edited through
1654       that link.
1655     * The  call  field_info()  will retrieve the original static size of
1656       the  field;  use  dynamic_field_info()  to  get the actual dynamic
1657       size.
1658
1659Field Validation
1660
1661   By  default,  a  field will accept any data that will fit in its input
1662   buffer.  However,  it  is  possible  to  attach a validation type to a
1663   field.  If  you  do  this,  any  attempt  to  leave the field while it
1664   contains  data  that doesn't match the validation type will fail. Some
1665   validation  types also have a character-validity check for each time a
1666   character is entered in the field.
1667
1668   A   field's   validation   check   (if   any)   is   not  called  when
1669   set_field_buffer()  modifies the input buffer, nor when that buffer is
1670   changed through a linked field.
1671
1672   The  form library provides a rich set of pre-defined validation types,
1673   and  gives  you  the capability to define custom ones of your own. You
1674   can  examine and change field validation attributes with the following
1675   functions:
1676int set_field_type(FIELD *field,          /* field to alter */
1677                   FIELDTYPE *ftype,      /* type to associate */
1678                   ...);                  /* additional arguments*/
1679
1680FIELDTYPE *field_type(FIELD *field);      /* field to query */
1681
1682   The  validation  type  of  a  field  is considered an attribute of the
1683   field.  As  with  other field attributes, Also, doing set_field_type()
1684   with  a  NULL  field  default  will  change  the  system  default  for
1685   validation of newly-created fields.
1686
1687   Here are the pre-defined validation types:
1688
1689  TYPE_ALPHA
1690
1691   This  field  type  accepts  alphabetic  data; no blanks, no digits, no
1692   special  characters  (this  is checked at character-entry time). It is
1693   set up with:
1694int set_field_type(FIELD *field,          /* field to alter */
1695                   TYPE_ALPHA,            /* type to associate */
1696                   int width);            /* maximum width of field */
1697
1698   The width argument sets a minimum width of data. Typically you'll want
1699   to  set this to the field width; if it's greater than the field width,
1700   the  validation  check will always fail. A minimum width of zero makes
1701   field completion optional.
1702
1703  TYPE_ALNUM
1704
1705   This  field  type  accepts  alphabetic  data and digits; no blanks, no
1706   special  characters  (this  is checked at character-entry time). It is
1707   set up with:
1708int set_field_type(FIELD *field,          /* field to alter */
1709                   TYPE_ALNUM,            /* type to associate */
1710                   int width);            /* maximum width of field */
1711
1712   The  width  argument sets a minimum width of data. As with TYPE_ALPHA,
1713   typically  you'll want to set this to the field width; if it's greater
1714   than the field width, the validation check will always fail. A minimum
1715   width of zero makes field completion optional.
1716
1717  TYPE_ENUM
1718
1719   This  type  allows  you  to  restrict  a  field's values to be among a
1720   specified  set  of  string  values (for example, the two-letter postal
1721   codes for U.S. states). It is set up with:
1722int set_field_type(FIELD *field,          /* field to alter */
1723                   TYPE_ENUM,             /* type to associate */
1724                   char **valuelist;      /* list of possible values */
1725                   int checkcase;         /* case-sensitive? */
1726                   int checkunique);      /* must specify uniquely? */
1727
1728   The  valuelist parameter must point at a NULL-terminated list of valid
1729   strings.  The  checkcase  argument, if true, makes comparison with the
1730   string case-sensitive.
1731
1732   When  the user exits a TYPE_ENUM field, the validation procedure tries
1733   to  complete  the  data  in the buffer to a valid entry. If a complete
1734   choice  string has been entered, it is of course valid. But it is also
1735   possible to enter a prefix of a valid string and have it completed for
1736   you.
1737
1738   By  default,  if  you enter such a prefix and it matches more than one
1739   value  in  the  string list, the prefix will be completed to the first
1740   matching value. But the checkunique argument, if true, requires prefix
1741   matches to be unique in order to be valid.
1742
1743   The   REQ_NEXT_CHOICE   and  REQ_PREV_CHOICE  input  requests  can  be
1744   particularly useful with these fields.
1745
1746  TYPE_INTEGER
1747
1748   This field type accepts an integer. It is set up as follows:
1749int set_field_type(FIELD *field,          /* field to alter */
1750                   TYPE_INTEGER,          /* type to associate */
1751                   int padding,           /* # places to zero-pad to */
1752                   int vmin, int vmax);   /* valid range */
1753
1754   Valid  characters consist of an optional leading minus and digits. The
1755   range check is performed on exit. If the range maximum is less than or
1756   equal to the minimum, the range is ignored.
1757
1758   If the value passes its range check, it is padded with as many leading
1759   zero digits as necessary to meet the padding argument.
1760
1761   A TYPE_INTEGER value buffer can conveniently be interpreted with the C
1762   library function atoi(3).
1763
1764  TYPE_NUMERIC
1765
1766   This field type accepts a decimal number. It is set up as follows:
1767int set_field_type(FIELD *field,              /* field to alter */
1768                   TYPE_NUMERIC,              /* type to associate */
1769                   int padding,               /* # places of precision */
1770                   double vmin, double vmax); /* valid range */
1771
1772   Valid  characters  consist  of  an  optional leading minus and digits.
1773   possibly  including a decimal point. If your system supports locale's,
1774   the  decimal  point  character  used  must  be the one defined by your
1775   locale.  The range check is performed on exit. If the range maximum is
1776   less than or equal to the minimum, the range is ignored.
1777
1778   If  the  value  passes  its  range  check,  it  is padded with as many
1779   trailing zero digits as necessary to meet the padding argument.
1780
1781   A TYPE_NUMERIC value buffer can conveniently be interpreted with the C
1782   library function atof(3).
1783
1784  TYPE_REGEXP
1785
1786   This  field type accepts data matching a regular expression. It is set
1787   up as follows:
1788int set_field_type(FIELD *field,          /* field to alter */
1789                   TYPE_REGEXP,           /* type to associate */
1790                   char *regexp);         /* expression to match */
1791
1792   The  syntax  for  regular expressions is that of regcomp(3). The check
1793   for regular-expression match is performed on exit.
1794
1795Direct Field Buffer Manipulation
1796
1797   The chief attribute of a field is its buffer contents. When a form has
1798   been  completed,  your  application usually needs to know the state of
1799   each field buffer. You can find this out with:
1800char *field_buffer(FIELD *field,          /* field to query */
1801                   int bufindex);         /* number of buffer to query */
1802
1803   Normally,  the state of the zero-numbered buffer for each field is set
1804   by  the user's editing actions on that field. It's sometimes useful to
1805   be  able  to set the value of the zero-numbered (or some other) buffer
1806   from your application:
1807int set_field_buffer(FIELD *field,        /* field to alter */
1808                   int bufindex,          /* number of buffer to alter */
1809                   char *value);          /* string value to set */
1810
1811   If  the  field  is  not  large  enough  and  cannot  be  resized  to a
1812   sufficiently large size to contain the specified value, the value will
1813   be truncated to fit.
1814
1815   Calling  field_buffer() with a null field pointer will raise an error.
1816   Calling  field_buffer()  on  a  field not currently selected for input
1817   will return a correct value. Calling field_buffer() on a field that is
1818   currently  selected for input may not necessarily give a correct field
1819   buffer  value, because entered data isn't necessarily copied to buffer
1820   zero  before the exit validation check. To guarantee that the returned
1821   buffer  value  reflects  on-screen reality, call field_buffer() either
1822   (1) in the field's exit validation check routine, (2) from the field's
1823   or  form's  initialization  or  termination hooks, or (3) just after a
1824   REQ_VALIDATION request has been processed by the forms driver.
1825
1826Attributes of Forms
1827
1828   As  with  field  attributes,  form attributes inherit a default from a
1829   system default form structure. These defaults can be queried or set by
1830   of these functions using a form-pointer argument of NULL.
1831
1832   The principal attribute of a form is its field list. You can query and
1833   change this list with:
1834int set_form_fields(FORM *form,           /* form to alter */
1835                    FIELD **fields);      /* fields to connect */
1836
1837char *form_fields(FORM *form);            /* fetch fields of form */
1838
1839int field_count(FORM *form);              /* count connect fields */
1840
1841   The  second  argument  of  set_form_fields()  may be a NULL-terminated
1842   field pointer array like the one required by new_form(). In that case,
1843   the  old  fields  of  the  form  are  disconnected  but not freed (and
1844   eligible  to  be  connected  to  other forms), then the new fields are
1845   connected.
1846
1847   It  may  also  be  null, in which case the old fields are disconnected
1848   (and not freed) but no new ones are connected.
1849
1850   The   field_count()  function  simply  counts  the  number  of  fields
1851   connected  to a given from. It returns -1 if the form-pointer argument
1852   is NULL.
1853
1854Control of Form Display
1855
1856   In  the  overview section, you saw that to display a form you normally
1857   start  by  defining  its size (and fields), posting it, and refreshing
1858   the  screen.  There  is  an  hidden  step before posting, which is the
1859   association  of  the  form  with  a  frame window (actually, a pair of
1860   windows)  within  which  it  will  be displayed. By default, the forms
1861   library associates every form with the full-screen window stdscr.
1862
1863   By making this step explicit, you can associate a form with a declared
1864   frame window on your screen display. This can be useful if you want to
1865   adapt  the  form  display  to different screen sizes, dynamically tile
1866   forms  on  the  screen,  or  use a form as part of an interface layout
1867   managed by panels.
1868
1869   The  two  windows associated with each form have the same functions as
1870   their  analogues  in  the menu library. Both these windows are painted
1871   when the form is posted and erased when the form is unposted.
1872
1873   The  outer  or  frame  window  is  not  otherwise  touched by the form
1874   routines. It exists so the programmer can associate a title, a border,
1875   or  perhaps  help text with the form and have it properly refreshed or
1876   erased at post/unpost time. The inner window or subwindow is where the
1877   current form page is actually displayed.
1878
1879   In  order  to declare your own frame window for a form, you'll need to
1880   know  the  size  of  the  form's  bounding rectangle. You can get this
1881   information with:
1882int scale_form(FORM *form,                /* form to query */
1883               int *rows,                 /* form rows */
1884               int *cols);                /* form cols */
1885
1886   The form dimensions are passed back in the locations pointed to by the
1887   arguments.  Once  you have this information, you can use it to declare
1888   of windows, then use one of these functions:
1889int set_form_win(FORM *form,              /* form to alter */
1890                 WINDOW *win);            /* frame window to connect */
1891
1892WINDOW *form_win(FORM *form);             /* fetch frame window of form */
1893
1894int set_form_sub(FORM *form,              /* form to alter */
1895                 WINDOW *win);            /* form subwindow to connect */
1896
1897WINDOW *form_sub(FORM *form);             /* fetch form subwindow of form */
1898
1899   Note  that curses operations, including refresh(), on the form, should
1900   be done on the frame window, not the form subwindow.
1901
1902   It  is  possible  to  check  from  your  application  whether all of a
1903   scrollable  field is actually displayed within the menu subwindow. Use
1904   these functions:
1905int data_ahead(FORM *form);               /* form to be queried */
1906
1907int data_behind(FORM *form);              /* form to be queried */
1908
1909   The  function  data_ahead()  returns  TRUE if (a) the current field is
1910   one-line  and  has  undisplayed data off to the right, (b) the current
1911   field is multi-line and there is data off-screen below it.
1912
1913   The function data_behind() returns TRUE if the first (upper left hand)
1914   character position is off-screen (not being displayed).
1915
1916   Finally,  there  is  a function to restore the form window's cursor to
1917   the value expected by the forms driver:
1918int pos_form_cursor(FORM *)               /* form to be queried */
1919
1920   If your application changes the form window cursor, call this function
1921   before   handing  control  back  to  the  forms  driver  in  order  to
1922   re-synchronize it.
1923
1924Input Processing in the Forms Driver
1925
1926   The function form_driver() handles virtualized input requests for form
1927   navigation, editing, and validation requests, just as menu_driver does
1928   for menus (see the section on menu input handling).
1929int form_driver(FORM *form,               /* form to pass input to */
1930                int request);             /* form request code */
1931
1932   Your  input  virtualization  function  needs  to  take  input and then
1933   convert  it  to  either an alphanumeric character (which is treated as
1934   data  to  be  entered  in  the  currently-selected  field), or a forms
1935   processing request.
1936
1937   The   forms   driver  provides  hooks  (through  input-validation  and
1938   field-termination  functions)  with  which  your  application code can
1939   check that the input taken by the driver matched what was expected.
1940
1941  Page Navigation Requests
1942
1943   These  requests  cause  page-level  moves through the form, triggering
1944   display of a new form screen.
1945
1946   REQ_NEXT_PAGE
1947          Move to the next form page.
1948
1949   REQ_PREV_PAGE
1950          Move to the previous form page.
1951
1952   REQ_FIRST_PAGE
1953          Move to the first form page.
1954
1955   REQ_LAST_PAGE
1956          Move to the last form page.
1957
1958   These  requests  treat the list as cyclic; that is, REQ_NEXT_PAGE from
1959   the last page goes to the first, and REQ_PREV_PAGE from the first page
1960   goes to the last.
1961
1962  Inter-Field Navigation Requests
1963
1964   These requests handle navigation between fields on the same page.
1965
1966   REQ_NEXT_FIELD
1967          Move to next field.
1968
1969   REQ_PREV_FIELD
1970          Move to previous field.
1971
1972   REQ_FIRST_FIELD
1973          Move to the first field.
1974
1975   REQ_LAST_FIELD
1976          Move to the last field.
1977
1978   REQ_SNEXT_FIELD
1979          Move to sorted next field.
1980
1981   REQ_SPREV_FIELD
1982          Move to sorted previous field.
1983
1984   REQ_SFIRST_FIELD
1985          Move to the sorted first field.
1986
1987   REQ_SLAST_FIELD
1988          Move to the sorted last field.
1989
1990   REQ_LEFT_FIELD
1991          Move left to field.
1992
1993   REQ_RIGHT_FIELD
1994          Move right to field.
1995
1996   REQ_UP_FIELD
1997          Move up to field.
1998
1999   REQ_DOWN_FIELD
2000          Move down to field.
2001
2002   These  requests treat the list of fields on a page as cyclic; that is,
2003   REQ_NEXT_FIELD   from   the   last   field  goes  to  the  first,  and
2004   REQ_PREV_FIELD from the first field goes to the last. The order of the
2005   fields for these (and the REQ_FIRST_FIELD and REQ_LAST_FIELD requests)
2006   is simply the order of the field pointers in the form array (as set up
2007   by new_form() or set_form_fields()
2008
2009   It  is also possible to traverse the fields as if they had been sorted
2010   in  screen-position  order,  so  the  sequence  goes left-to-right and
2011   top-to-bottom.   To   do   this,   use   the   second  group  of  four
2012   sorted-movement requests.
2013
2014   Finally, it is possible to move between fields using visual directions
2015   up,  down, right, and left. To accomplish this, use the third group of
2016   four requests. Note, however, that the position of a form for purposes
2017   of these requests is its upper-left corner.
2018
2019   For   example,  suppose  you  have  a  multi-line  field  B,  and  two
2020   single-line fields A and C on the same line with B, with A to the left
2021   of  B  and  C  to the right of B. A REQ_MOVE_RIGHT from A will go to B
2022   only  if  A, B, and C all share the same first line; otherwise it will
2023   skip over B to C.
2024
2025  Intra-Field Navigation Requests
2026
2027   These  requests drive movement of the edit cursor within the currently
2028   selected field.
2029
2030   REQ_NEXT_CHAR
2031          Move to next character.
2032
2033   REQ_PREV_CHAR
2034          Move to previous character.
2035
2036   REQ_NEXT_LINE
2037          Move to next line.
2038
2039   REQ_PREV_LINE
2040          Move to previous line.
2041
2042   REQ_NEXT_WORD
2043          Move to next word.
2044
2045   REQ_PREV_WORD
2046          Move to previous word.
2047
2048   REQ_BEG_FIELD
2049          Move to beginning of field.
2050
2051   REQ_END_FIELD
2052          Move to end of field.
2053
2054   REQ_BEG_LINE
2055          Move to beginning of line.
2056
2057   REQ_END_LINE
2058          Move to end of line.
2059
2060   REQ_LEFT_CHAR
2061          Move left in field.
2062
2063   REQ_RIGHT_CHAR
2064          Move right in field.
2065
2066   REQ_UP_CHAR
2067          Move up in field.
2068
2069   REQ_DOWN_CHAR
2070          Move down in field.
2071
2072   Each  word  is  separated  from  the  previous  and next characters by
2073   whitespace. The commands to move to beginning and end of line or field
2074   look for the first or last non-pad character in their ranges.
2075
2076  Scrolling Requests
2077
2078   Fields  that  are dynamic and have grown and fields explicitly created
2079   with   offscreen   rows   are   scrollable.   One-line  fields  scroll
2080   horizontally;  multi-line  fields scroll vertically. Most scrolling is
2081   triggered by editing and intra-field movement (the library scrolls the
2082   field  to  keep  the  cursor  visible).  It  is possible to explicitly
2083   request scrolling with the following requests:
2084
2085   REQ_SCR_FLINE
2086          Scroll vertically forward a line.
2087
2088   REQ_SCR_BLINE
2089          Scroll vertically backward a line.
2090
2091   REQ_SCR_FPAGE
2092          Scroll vertically forward a page.
2093
2094   REQ_SCR_BPAGE
2095          Scroll vertically backward a page.
2096
2097   REQ_SCR_FHPAGE
2098          Scroll vertically forward half a page.
2099
2100   REQ_SCR_BHPAGE
2101          Scroll vertically backward half a page.
2102
2103   REQ_SCR_FCHAR
2104          Scroll horizontally forward a character.
2105
2106   REQ_SCR_BCHAR
2107          Scroll horizontally backward a character.
2108
2109   REQ_SCR_HFLINE
2110          Scroll horizontally one field width forward.
2111
2112   REQ_SCR_HBLINE
2113          Scroll horizontally one field width backward.
2114
2115   REQ_SCR_HFHALF
2116          Scroll horizontally one half field width forward.
2117
2118   REQ_SCR_HBHALF
2119          Scroll horizontally one half field width backward.
2120
2121   For scrolling purposes, a page of a field is the height of its visible
2122   part.
2123
2124  Editing Requests
2125
2126   When  you pass the forms driver an ASCII character, it is treated as a
2127   request  to add the character to the field's data buffer. Whether this
2128   is  an  insertion  or  a  replacement depends on the field's edit mode
2129   (insertion is the default.
2130
2131   The following requests support editing the field and changing the edit
2132   mode:
2133
2134   REQ_INS_MODE
2135          Set insertion mode.
2136
2137   REQ_OVL_MODE
2138          Set overlay mode.
2139
2140   REQ_NEW_LINE
2141          New line request (see below for explanation).
2142
2143   REQ_INS_CHAR
2144          Insert space at character location.
2145
2146   REQ_INS_LINE
2147          Insert blank line at character location.
2148
2149   REQ_DEL_CHAR
2150          Delete character at cursor.
2151
2152   REQ_DEL_PREV
2153          Delete previous word at cursor.
2154
2155   REQ_DEL_LINE
2156          Delete line at cursor.
2157
2158   REQ_DEL_WORD
2159          Delete word at cursor.
2160
2161   REQ_CLR_EOL
2162          Clear to end of line.
2163
2164   REQ_CLR_EOF
2165          Clear to end of field.
2166
2167   REQ_CLEAR_FIELD
2168          Clear entire field.
2169
2170   The   behavior  of  the  REQ_NEW_LINE  and  REQ_DEL_PREV  requests  is
2171   complicated  and  partly  controlled  by  a pair of forms options. The
2172   special  cases  are triggered when the cursor is at the beginning of a
2173   field, or on the last line of the field.
2174
2175   First, we consider REQ_NEW_LINE:
2176
2177   The  normal  behavior  of  REQ_NEW_LINE in insert mode is to break the
2178   current line at the position of the edit cursor, inserting the portion
2179   of  the  current  line  after  the  cursor as a new line following the
2180   current  and  moving the cursor to the beginning of that new line (you
2181   may think of this as inserting a newline in the field buffer).
2182
2183   The  normal  behavior  of REQ_NEW_LINE in overlay mode is to clear the
2184   current  line from the position of the edit cursor to end of line. The
2185   cursor is then moved to the beginning of the next line.
2186
2187   However, REQ_NEW_LINE at the beginning of a field, or on the last line
2188   of  a  field,  instead  does a REQ_NEXT_FIELD. O_NL_OVERLOAD option is
2189   off, this special action is disabled.
2190
2191   Now, let us consider REQ_DEL_PREV:
2192
2193   The  normal  behavior  of  REQ_DEL_PREV  is  to  delete  the  previous
2194   character.  If  insert mode is on, and the cursor is at the start of a
2195   line,  and  the  text  on  that  line will fit on the previous one, it
2196   instead  appends  the contents of the current line to the previous one
2197   and  deletes  the  current  line  (you may think of this as deleting a
2198   newline from the field buffer).
2199
2200   However,  REQ_DEL_PREV  at the beginning of a field is instead treated
2201   as a REQ_PREV_FIELD.
2202
2203   If  the  O_BS_OVERLOAD  option is off, this special action is disabled
2204   and the forms driver just returns E_REQUEST_DENIED.
2205
2206   See  Form  Options for discussion of how to set and clear the overload
2207   options.
2208
2209  Order Requests
2210
2211   If the type of your field is ordered, and has associated functions for
2212   getting  the  next and previous values of the type from a given value,
2213   there are requests that can fetch that value into the field buffer:
2214
2215   REQ_NEXT_CHOICE
2216          Place the successor value of the current value in the buffer.
2217
2218   REQ_PREV_CHOICE
2219          Place the predecessor value of the current value in the buffer.
2220
2221   Of the built-in field types, only TYPE_ENUM has built-in successor and
2222   predecessor  functions.  When you define a field type of your own (see
2223   Custom   Validation   Types),  you  can  associate  our  own  ordering
2224   functions.
2225
2226  Application Commands
2227
2228   Form  requests  are  represented  as  integers  above the curses value
2229   greater   than  KEY_MAX  and  less  than  or  equal  to  the  constant
2230   MAX_COMMAND.  If  your  input-virtualization  routine  returns a value
2231   above MAX_COMMAND, the forms driver will ignore it.
2232
2233Field Change Hooks
2234
2235   It  is  possible  to  set  function  hooks to be executed whenever the
2236   current  field  or  form  changes. Here are the functions that support
2237   this:
2238typedef void    (*HOOK)();       /* pointer to function returning void */
2239
2240int set_form_init(FORM *form,    /* form to alter */
2241                  HOOK hook);    /* initialization hook */
2242
2243HOOK form_init(FORM *form);      /* form to query */
2244
2245int set_form_term(FORM *form,    /* form to alter */
2246                  HOOK hook);    /* termination hook */
2247
2248HOOK form_term(FORM *form);      /* form to query */
2249
2250int set_field_init(FORM *form,   /* form to alter */
2251                  HOOK hook);    /* initialization hook */
2252
2253HOOK field_init(FORM *form);     /* form to query */
2254
2255int set_field_term(FORM *form,   /* form to alter */
2256                  HOOK hook);    /* termination hook */
2257
2258HOOK field_term(FORM *form);     /* form to query */
2259
2260   These functions allow you to either set or query four different hooks.
2261   In  each  of  the  set  functions,  the  second argument should be the
2262   address  of a hook function. These functions differ only in the timing
2263   of the hook call.
2264
2265   form_init
2266          This  hook  is called when the form is posted; also, just after
2267          each page change operation.
2268
2269   field_init
2270          This  hook  is called when the form is posted; also, just after
2271          each field change
2272
2273   field_term
2274          This  hook is called just after field validation; that is, just
2275          before the field is altered. It is also called when the form is
2276          unposted.
2277
2278   form_term
2279          This  hook  is  called  when  the  form is unposted; also, just
2280          before each page change operation.
2281
2282   Calls to these hooks may be triggered
2283    1. When user editing requests are processed by the forms driver
2284    2. When the current page is changed by set_current_field() call
2285    3. When the current field is changed by a set_form_page() call
2286
2287   See Field Change Commands for discussion of the latter two cases.
2288
2289   You  can  set  a default hook for all fields by passing one of the set
2290   functions a NULL first argument.
2291
2292   You  can  disable  any of these hooks by (re)setting them to NULL, the
2293   default value.
2294
2295Field Change Commands
2296
2297   Normally,  navigation  through  the  form will be driven by the user's
2298   input  requests.  But  sometimes  it  is useful to be able to move the
2299   focus  for  editing  and viewing under control of your application, or
2300   ask  which  field it currently is in. The following functions help you
2301   accomplish this:
2302int set_current_field(FORM *form,         /* form to alter */
2303                      FIELD *field);      /* field to shift to */
2304
2305FIELD *current_field(FORM *form);         /* form to query */
2306
2307int field_index(FORM *form,               /* form to query */
2308                FIELD *field);            /* field to get index of */
2309
2310   The function field_index() returns the index of the given field in the
2311   given   form's   field  array  (the  array  passed  to  new_form()  or
2312   set_form_fields()).
2313
2314   The  initial  current field of a form is the first active field on the
2315   first page. The function set_form_fields() resets this.
2316
2317   It is also possible to move around by pages.
2318int set_form_page(FORM *form,             /* form to alter */
2319                  int page);              /* page to go to (0-origin) */
2320
2321int form_page(FORM *form);                /* return form's current page */
2322
2323   The   initial  page  of  a  newly-created  form  is  0.  The  function
2324   set_form_fields() resets this.
2325
2326Form Options
2327
2328   Like  fields,  forms may have control option bits. They can be changed
2329   or queried with these functions:
2330int set_form_opts(FORM *form,             /* form to alter */
2331                  int attr);              /* attribute to set */
2332
2333int form_opts_on(FORM *form,              /* form to alter */
2334                 int attr);               /* attributes to turn on */
2335
2336int form_opts_off(FORM *form,             /* form to alter */
2337                  int attr);              /* attributes to turn off */
2338
2339int form_opts(FORM *form);                /* form to query */
2340
2341   By default, all options are on. Here are the available option bits:
2342
2343   O_NL_OVERLOAD
2344          Enable  overloading  of  REQ_NEW_LINE  as  described in Editing
2345          Requests. The value of this option is ignored on dynamic fields
2346          that  have  not  reached  their  size limit; these have no last
2347          line,  so  the  circumstances  for  triggering a REQ_NEXT_FIELD
2348          never arise.
2349
2350   O_BS_OVERLOAD
2351          Enable  overloading  of  REQ_DEL_PREV  as  described in Editing
2352          Requests.
2353
2354   The option values are bit-masks and can be composed with logical-or in
2355   the obvious way.
2356
2357Custom Validation Types
2358
2359   The  form library gives you the capability to define custom validation
2360   types  of  your  own.  Further,  the  optional additional arguments of
2361   set_field_type effectively allow you to parameterize validation types.
2362   Most  of the complications in the validation-type interface have to do
2363   with the handling of the additional arguments within custom validation
2364   functions.
2365
2366  Union Types
2367
2368   The  simplest  way  to create a custom data type is to compose it from
2369   two preexisting ones:
2370FIELD *link_fieldtype(FIELDTYPE *type1,
2371                      FIELDTYPE *type2);
2372
2373   This  function creates a field type that will accept any of the values
2374   legal  for  either  of  its  argument field types (which may be either
2375   predefined  or  programmer-defined).  If a set_field_type() call later
2376   requires  arguments,  the new composite type expects all arguments for
2377   the  first  type,  than  all arguments for the second. Order functions
2378   (see  Order Requests) associated with the component types will work on
2379   the  composite;  what it does is check the validation function for the
2380   first  type,  then  for  the  second,  to  figure what type the buffer
2381   contents should be treated as.
2382
2383  New Field Types
2384
2385   To  create  a field type from scratch, you need to specify one or both
2386   of the following things:
2387     * A  character-validation function, to check each character as it is
2388       entered.
2389     * A field-validation function to be applied on exit from the field.
2390
2391   Here's how you do that:
2392typedef int     (*HOOK)();       /* pointer to function returning int */
2393
2394FIELDTYPE *new_fieldtype(HOOK f_validate, /* field validator */
2395                         HOOK c_validate) /* character validator */
2396
2397
2398int free_fieldtype(FIELDTYPE *ftype);     /* type to free */
2399
2400   At least one of the arguments of new_fieldtype() must be non-NULL. The
2401   forms  driver  will  automatically  call  the  new  type's  validation
2402   functions at appropriate points in processing a field of the new type.
2403
2404   The  function  free_fieldtype()  deallocates  the  argument fieldtype,
2405   freeing all storage associated with it.
2406
2407   Normally,  a field validator is called when the user attempts to leave
2408   the  field.  Its  first argument is a field pointer, from which it can
2409   get  to  field buffer 0 and test it. If the function returns TRUE, the
2410   operation  succeeds; if it returns FALSE, the edit cursor stays in the
2411   field.
2412
2413   A  character  validator  gets  the  character  passed  in  as  a first
2414   argument.  It  too should return TRUE if the character is valid, FALSE
2415   otherwise.
2416
2417  Validation Function Arguments
2418
2419   Your  field-  and  character-  validation  functions  will be passed a
2420   second  argument  as  well.  This  second argument is the address of a
2421   structure   (which   we'll   call  a  pile)  built  from  any  of  the
2422   field-type-specific  arguments  passed to set_field_type(). If no such
2423   arguments  are  defined for the field type, this pile pointer argument
2424   will be NULL.
2425
2426   In order to arrange for such arguments to be passed to your validation
2427   functions,  you  must  associate  a  small  set  of storage-management
2428   functions with the type. The forms driver will use these to synthesize
2429   a  pile from the trailing arguments of each set_field_type() argument,
2430   and a pointer to the pile will be passed to the validation functions.
2431
2432   Here is how you make the association:
2433typedef char    *(*PTRHOOK)();    /* pointer to function returning (char *) */
2434typedef void    (*VOIDHOOK)();    /* pointer to function returning void */
2435
2436int set_fieldtype_arg(FIELDTYPE *type,    /* type to alter */
2437                      PTRHOOK make_str,   /* make structure from args */
2438                      PTRHOOK copy_str,   /* make copy of structure */
2439                      VOIDHOOK free_str); /* free structure storage */
2440
2441   Here is how the storage-management hooks are used:
2442
2443   make_str
2444          This  function  is  called  by  set_field_type().  It  gets one
2445          argument,  a  va_list  of the type-specific arguments passed to
2446          set_field_type().  It is expected to return a pile pointer to a
2447          data structure that encapsulates those arguments.
2448
2449   copy_str
2450          This function is called by form library functions that allocate
2451          new  field  instances.  It  is expected to take a pile pointer,
2452          copy  the  pile to allocated storage, and return the address of
2453          the pile copy.
2454
2455   free_str
2456          This   function  is  called  by  field-  and  type-deallocation
2457          routines  in the library. It takes a pile pointer argument, and
2458          is expected to free the storage of that pile.
2459
2460   The  make_str  and  copy_str  functions  may  return  NULL  to  signal
2461   allocation  failure.  The  library  routines  will that call them will
2462   return  error  indication  when  this  happens.  Thus, your validation
2463   functions  should  never  see  a  NULL file pointer and need not check
2464   specially for it.
2465
2466  Order Functions For Custom Types
2467
2468   Some  custom  field  types are simply ordered in the same well-defined
2469   way  that  TYPE_ENUM  is.  For  such  types,  it is possible to define
2470   successor and predecessor functions to support the REQ_NEXT_CHOICE and
2471   REQ_PREV_CHOICE requests. Here's how:
2472typedef int     (*INTHOOK)();     /* pointer to function returning int */
2473
2474int set_fieldtype_arg(FIELDTYPE *type,    /* type to alter */
2475                      INTHOOK succ,       /* get successor value */
2476                      INTHOOK pred);      /* get predecessor value */
2477
2478   The  successor  and  predecessor  arguments  will  each  be passed two
2479   arguments;  a field pointer, and a pile pointer (as for the validation
2480   functions).  They  are  expected to use the function field_buffer() to
2481   read  the current value, and set_field_buffer() on buffer 0 to set the
2482   next  or  previous  value.  Either  hook  may  return TRUE to indicate
2483   success  (a legal next or previous value was set) or FALSE to indicate
2484   failure.
2485
2486  Avoiding Problems
2487
2488   The  interface  for  defining  custom types is complicated and tricky.
2489   Rather  than attempting to create a custom type entirely from scratch,
2490   you  should start by studying the library source code for whichever of
2491   the pre-defined types seems to be closest to what you want.
2492
2493   Use  that code as a model, and evolve it towards what you really want.
2494   You  will avoid many problems and annoyances that way. The code in the
2495   ncurses  library  has  been  specifically  exempted  from  the package
2496   copyright to support this.
2497
2498   If  your  custom  type  defines  order  functions,  have  do something
2499   intuitive  with  a  blank  field.  A  useful convention is to make the
2500   successor   of  a  blank  field  the  types  minimum  value,  and  its
2501   predecessor the maximum.
2502