1<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 3.0//EN"> 2<!-- 3 $Id: ncurses-intro.html,v 1.43 2007/03/03 19:31:50 tom Exp $ 4 **************************************************************************** 5 * Copyright (c) 1998-2006,2007 Free Software Foundation, Inc. * 6 * * 7 * Permission is hereby granted, free of charge, to any person obtaining a * 8 * copy of this software and associated documentation files (the * 9 * "Software"), to deal in the Software without restriction, including * 10 * without limitation the rights to use, copy, modify, merge, publish, * 11 * distribute, distribute with modifications, sublicense, and/or sell * 12 * copies of the Software, and to permit persons to whom the Software is * 13 * furnished to do so, subject to the following conditions: * 14 * * 15 * The above copyright notice and this permission notice shall be included * 16 * in all copies or substantial portions of the Software. * 17 * * 18 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS * 19 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF * 20 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. * 21 * IN NO EVENT SHALL THE ABOVE COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, * 22 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR * 23 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR * 24 * THE USE OR OTHER DEALINGS IN THE SOFTWARE. * 25 * * 26 * Except as contained in this notice, the name(s) of the above copyright * 27 * holders shall not be used in advertising or otherwise to promote the * 28 * sale, use or other dealings in this Software without prior written * 29 * authorization. * 30 **************************************************************************** 31--> 32<HTML> 33<HEAD> 34<TITLE>Writing Programs with NCURSES</TITLE> 35<link rev="made" href="mailto:bugs-ncurses@gnu.org"> 36<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> 37</HEAD> 38<BODY> 39 40<H1>Writing Programs with NCURSES</H1> 41 42<BLOCKQUOTE> 43by Eric S. Raymond and Zeyd M. Ben-Halim<BR> 44updates since release 1.9.9e by Thomas Dickey 45</BLOCKQUOTE> 46 47<H1>Contents</H1> 48<UL> 49<LI><A HREF="#introduction">Introduction</A> 50<UL> 51<LI><A HREF="#history">A Brief History of Curses</A> 52<LI><A HREF="#scope">Scope of This Document</A> 53<LI><A HREF="#terminology">Terminology</A> 54</UL> 55<LI><A HREF="#curses">The Curses Library</A> 56<UL> 57<LI><A HREF="#overview">An Overview of Curses</A> 58<UL> 59<LI><A HREF="#compiling">Compiling Programs using Curses</A> 60<LI><A HREF="#updating">Updating the Screen</A> 61<LI><A HREF="#stdscr">Standard Windows and Function Naming Conventions</A> 62<LI><A HREF="#variables">Variables</A> 63</UL> 64<LI><A HREF="#using">Using the Library</A> 65<UL> 66<LI><A HREF="#starting">Starting up</A> 67<LI><A HREF="#output">Output</A> 68<LI><A HREF="#input">Input</A> 69<LI><A HREF="#formschars">Using Forms Characters</A> 70<LI><A HREF="#attributes">Character Attributes and Color</A> 71<LI><A HREF="#mouse">Mouse Interfacing</A> 72<LI><A HREF="#finishing">Finishing Up</A> 73</UL> 74<LI><A HREF="#functions">Function Descriptions</A> 75<UL> 76<LI><A HREF="#init">Initialization and Wrapup</A> 77<LI><A HREF="#flush">Causing Output to the Terminal</A> 78<LI><A HREF="#lowlevel">Low-Level Capability Access</A> 79<LI><A HREF="#debugging">Debugging</A> 80</UL> 81<LI><A HREF="#hints">Hints, Tips, and Tricks</A> 82<UL> 83<LI><A HREF="#caution">Some Notes of Caution</A> 84<LI><A HREF="#leaving">Temporarily Leaving ncurses Mode</A> 85<LI><A HREF="#xterm">Using <CODE>ncurses</CODE> under <CODE>xterm</CODE></A> 86<LI><A HREF="#screens">Handling Multiple Terminal Screens</A> 87<LI><A HREF="#testing">Testing for Terminal Capabilities</A> 88<LI><A HREF="#tuning">Tuning for Speed</A> 89<LI><A HREF="#special">Special Features of <CODE>ncurses</CODE></A> 90</UL> 91<LI><A HREF="#compat">Compatibility with Older Versions</A> 92<UL> 93<LI><A HREF="#refbug">Refresh of Overlapping Windows</A> 94<LI><A HREF="#backbug">Background Erase</A> 95</UL> 96<LI><A HREF="#xsifuncs">XSI Curses Conformance</A> 97</UL> 98<LI><A HREF="#panels">The Panels Library</A> 99<UL> 100<LI><A HREF="#pcompile">Compiling With the Panels Library</A> 101<LI><A HREF="#poverview">Overview of Panels</A> 102<LI><A HREF="#pstdscr">Panels, Input, and the Standard Screen</A> 103<LI><A HREF="#hiding">Hiding Panels</A> 104<LI><A HREF="#pmisc">Miscellaneous Other Facilities</A> 105</UL> 106<LI><A HREF="#menu">The Menu Library</A> 107<UL> 108<LI><A HREF="#mcompile">Compiling with the menu Library</A> 109<LI><A HREF="#moverview">Overview of Menus</A> 110<LI><A HREF="#mselect">Selecting items</A> 111<LI><A HREF="#mdisplay">Menu Display</A> 112<LI><A HREF="#mwindows">Menu Windows</A> 113<LI><A HREF="#minput">Processing Menu Input</A> 114<LI><A HREF="#mmisc">Miscellaneous Other Features</A> 115</UL> 116<LI><A HREF="#form">The Forms Library</A> 117<UL> 118<LI><A HREF="#fcompile">Compiling with the forms Library</A> 119<LI><A HREF="#foverview">Overview of Forms</A> 120<LI><A HREF="#fcreate">Creating and Freeing Fields and Forms</A> 121<LI><A HREF="#fattributes">Fetching and Changing Field Attributes</A> 122<UL> 123<LI><A HREF="#fsizes">Fetching Size and Location Data</A> 124<LI><A HREF="#flocation">Changing the Field Location</A> 125<LI><A HREF="#fjust">The Justification Attribute</A> 126<LI><A HREF="#fdispatts">Field Display Attributes</A> 127<LI><A HREF="#foptions">Field Option Bits</A> 128<LI><A HREF="#fstatus">Field Status</A> 129<LI><A HREF="#fuser">Field User Pointer</A> 130</UL> 131<LI><A HREF="#fdynamic">Variable-Sized Fields</A> 132<LI><A HREF="#fvalidation">Field Validation</A> 133<UL> 134<LI><A HREF="#ftype_alpha">TYPE_ALPHA</A> 135<LI><A HREF="#ftype_alnum">TYPE_ALNUM</A> 136<LI><A HREF="#ftype_enum">TYPE_ENUM</A> 137<LI><A HREF="#ftype_integer">TYPE_INTEGER</A> 138<LI><A HREF="#ftype_numeric">TYPE_NUMERIC</A> 139<LI><A HREF="#ftype_regexp">TYPE_REGEXP</A> 140</UL> 141<LI><A HREF="#fbuffer">Direct Field Buffer Manipulation</A> 142<LI><A HREF="#formattrs">Attributes of Forms</A> 143<LI><A HREF="#fdisplay">Control of Form Display</A> 144<LI><A HREF="#fdriver">Input Processing in the Forms Driver</A> 145<UL> 146<LI><A HREF="#fpage">Page Navigation Requests</A> 147<LI><A HREF="#ffield">Inter-Field Navigation Requests</A> 148<LI><A HREF="#fifield">Intra-Field Navigation Requests</A> 149<LI><A HREF="#fscroll">Scrolling Requests</A> 150<LI><A HREF="#fedit">Field Editing Requests</A> 151<LI><A HREF="#forder">Order Requests</A> 152<LI><A HREF="#fappcmds">Application Commands</A> 153</UL> 154<LI><A HREF="#fhooks">Field Change Hooks</A> 155<LI><A HREF="#ffocus">Field Change Commands</A> 156<LI><A HREF="#frmoptions">Form Options</A> 157<LI><A HREF="#fcustom">Custom Validation Types</A> 158<UL> 159<LI><A HREF="#flinktypes">Union Types</A> 160<LI><A HREF="#fnewtypes">New Field Types</A> 161<LI><A HREF="#fcheckargs">Validation Function Arguments</A> 162<LI><A HREF="#fcustorder">Order Functions For Custom Types</A> 163<LI><A HREF="#fcustprobs">Avoiding Problems</A> 164</UL> 165</UL> 166</UL> 167 168<HR> 169<H1><A NAME="introduction">Introduction</A></H1> 170 171This document is an introduction to programming with <CODE>curses</CODE>. It is 172not an exhaustive reference for the curses Application Programming Interface 173(API); that role is filled by the <CODE>curses</CODE> manual pages. Rather, it 174is intended to help C programmers ease into using the package. <P> 175 176This document is aimed at C applications programmers not yet specifically 177familiar with ncurses. If you are already an experienced <CODE>curses</CODE> 178programmer, you should nevertheless read the sections on 179<A HREF="#mouse">Mouse Interfacing</A>, <A HREF="#debugging">Debugging</A>, 180<A HREF="#compat">Compatibility with Older Versions</A>, 181and <A HREF="#hints">Hints, Tips, and Tricks</A>. These will bring you up 182to speed on the special features and quirks of the <CODE>ncurses</CODE> 183implementation. If you are not so experienced, keep reading. <P> 184 185The <CODE>curses</CODE> package is a subroutine library for 186terminal-independent screen-painting and input-event handling which 187presents a high level screen model to the programmer, hiding differences 188between terminal types and doing automatic optimization of output to change 189one screen full of text into another. <CODE>Curses</CODE> uses terminfo, which 190is a database format that can describe the capabilities of thousands of 191different terminals. <P> 192 193The <CODE>curses</CODE> API may seem something of an archaism on UNIX desktops 194increasingly dominated by X, Motif, and Tcl/Tk. Nevertheless, UNIX still 195supports tty lines and X supports <EM>xterm(1)</EM>; the <CODE>curses</CODE> 196API has the advantage of (a) back-portability to character-cell terminals, 197and (b) simplicity. For an application that does not require bit-mapped 198graphics and multiple fonts, an interface implementation using <CODE>curses</CODE> 199will typically be a great deal simpler and less expensive than one using an 200X toolkit. 201 202<H2><A NAME="history">A Brief History of Curses</A></H2> 203 204Historically, the first ancestor of <CODE>curses</CODE> was the routines written to 205provide screen-handling for the game <CODE>rogue</CODE>; these used the 206already-existing <CODE>termcap</CODE> database facility for describing terminal 207capabilities. These routines were abstracted into a documented library and 208first released with the early BSD UNIX versions. <P> 209 210System III UNIX from Bell Labs featured a rewritten and much-improved 211<CODE>curses</CODE> library. It introduced the terminfo format. Terminfo is based 212on Berkeley's termcap database, but contains a number of improvements and 213extensions. Parameterized capabilities strings were introduced, making it 214possible to describe multiple video attributes, and colors and to handle far 215more unusual terminals than possible with termcap. In the later AT&T 216System V releases, <CODE>curses</CODE> evolved to use more facilities and offer 217more capabilities, going far beyond BSD curses in power and flexibility. 218 219<H2><A NAME="scope">Scope of This Document</A></H2> 220 221This document describes <CODE>ncurses</CODE>, a free implementation of 222the System V <CODE>curses</CODE> API with some clearly marked extensions. 223It includes the following System V curses features: 224<UL> 225<LI>Support for multiple screen highlights (BSD curses could only 226handle one `standout' highlight, usually reverse-video). 227<LI>Support for line- and box-drawing using forms characters. 228<LI>Recognition of function keys on input. 229<LI>Color support. 230<LI>Support for pads (windows of larger than screen size on which the 231screen or a subwindow defines a viewport). 232</UL> 233 234Also, this package makes use of the insert and delete line and character 235features of terminals so equipped, and determines how to optimally use these 236features with no help from the programmer. It allows arbitrary combinations of 237video attributes to be displayed, even on terminals that leave ``magic 238cookies'' on the screen to mark changes in attributes. <P> 239 240The <CODE>ncurses</CODE> package can also capture and use event reports from a 241mouse in some environments (notably, xterm under the X window system). This 242document includes tips for using the mouse. <P> 243 244The <CODE>ncurses</CODE> package was originated by Pavel Curtis. The original 245maintainer of this package is 246<A HREF="mailto:zmbenhal@netcom.com">Zeyd Ben-Halim</A> 247<zmbenhal@netcom.com>. 248<A HREF="mailto:esr@snark.thyrsus.com">Eric S. Raymond</A> 249<esr@snark.thyrsus.com> 250wrote many of the new features in versions after 1.8.1 251and wrote most of this introduction. 252Jürgen Pfeifer 253wrote all of the menu and forms code as well as the 254<A HREF="http://www.adahome.com">Ada95</A> binding. 255Ongoing work is being done by 256<A HREF="mailto:dickey@invisible-island.net">Thomas Dickey</A> (maintainer). 257Contact the current maintainers at 258<A HREF="mailto:bug-ncurses@gnu.org">bug-ncurses@gnu.org</A>. 259<P> 260 261This document also describes the <A HREF="#panels">panels</A> extension library, 262similarly modeled on the SVr4 panels facility. This library allows you to 263associate backing store with each of a stack or deck of overlapping windows, 264and provides operations for moving windows around in the stack that change 265their visibility in the natural way (handling window overlaps). <P> 266 267Finally, this document describes in detail the <A HREF="#menu">menus</A> and <A 268HREF="#form">forms</A> extension libraries, also cloned from System V, 269which support easy construction and sequences of menus and fill-in 270forms. 271 272 273<H2><A NAME="terminology">Terminology</A></H2> 274 275In this document, the following terminology is used with reasonable 276consistency: 277 278<DL> 279<DT> window 280<DD> 281A data structure describing a sub-rectangle of the screen (possibly the 282entire screen). You can write to a window as though it were a miniature 283screen, scrolling independently of other windows on the physical screen. 284<DT> screens 285<DD> 286A subset of windows which are as large as the terminal screen, i.e., they start 287at the upper left hand corner and encompass the lower right hand corner. One 288of these, <CODE>stdscr</CODE>, is automatically provided for the programmer. 289<DT> terminal screen 290<DD> 291The package's idea of what the terminal display currently looks like, i.e., 292what the user sees now. This is a special screen. 293</DL> 294 295<H1><A NAME="curses">The Curses Library</A></H1> 296 297<H2><A NAME="overview">An Overview of Curses</A></H2> 298 299<H3><A NAME="compiling">Compiling Programs using Curses</A></H3> 300 301In order to use the library, it is necessary to have certain types and 302variables defined. Therefore, the programmer must have a line: 303 304<PRE> 305 #include <curses.h> 306</PRE> 307 308at the top of the program source. The screen package uses the Standard I/O 309library, so <CODE><curses.h></CODE> includes 310<CODE><stdio.h></CODE>. <CODE><curses.h></CODE> also includes 311<CODE><termios.h></CODE>, <CODE><termio.h></CODE>, or 312<CODE><sgtty.h></CODE> depending on your system. It is redundant (but 313harmless) for the programmer to do these includes, too. In linking with 314<CODE>curses</CODE> you need to have <CODE>-lncurses</CODE> in your LDFLAGS or on the 315command line. There is no need for any other libraries. 316 317<H3><A NAME="updating">Updating the Screen</A></H3> 318 319In order to update the screen optimally, it is necessary for the routines to 320know what the screen currently looks like and what the programmer wants it to 321look like next. For this purpose, a data type (structure) named WINDOW is 322defined which describes a window image to the routines, including its starting 323position on the screen (the (y, x) coordinates of the upper left hand corner) 324and its size. One of these (called <CODE>curscr</CODE>, for current screen) is a 325screen image of what the terminal currently looks like. Another screen (called 326<CODE>stdscr</CODE>, for standard screen) is provided by default to make changes 327on. <P> 328 329A window is a purely internal representation. It is used to build and store a 330potential image of a portion of the terminal. It doesn't bear any necessary 331relation to what is really on the terminal screen; it's more like a 332scratchpad or write buffer. <P> 333 334To make the section of physical screen corresponding to a window reflect the 335contents of the window structure, the routine <CODE>refresh()</CODE> (or 336<CODE>wrefresh()</CODE> if the window is not <CODE>stdscr</CODE>) is called. <P> 337 338A given physical screen section may be within the scope of any number of 339overlapping windows. Also, changes can be made to windows in any order, 340without regard to motion efficiency. Then, at will, the programmer can 341effectively say ``make it look like this,'' and let the package implementation 342determine the most efficient way to repaint the screen. 343 344<H3><A NAME="stdscr">Standard Windows and Function Naming Conventions</A></H3> 345 346As hinted above, the routines can use several windows, but two are 347automatically given: <CODE>curscr</CODE>, which knows what the terminal looks like, 348and <CODE>stdscr</CODE>, which is what the programmer wants the terminal to look 349like next. The user should never actually access <CODE>curscr</CODE> directly. 350Changes should be made to through the API, and then the routine 351<CODE>refresh()</CODE> (or <CODE>wrefresh()</CODE>) called. <P> 352 353Many functions are defined to use <CODE>stdscr</CODE> as a default screen. For 354example, to add a character to <CODE>stdscr</CODE>, one calls <CODE>addch()</CODE> with 355the desired character as argument. To write to a different window. use the 356routine <CODE>waddch()</CODE> (for `w'indow-specific addch()) is provided. This 357convention of prepending function names with a `w' when they are to be 358applied to specific windows is consistent. The only routines which do not 359follow it are those for which a window must always be specified. <P> 360 361In order to move the current (y, x) coordinates from one point to another, the 362routines <CODE>move()</CODE> and <CODE>wmove()</CODE> are provided. However, it is 363often desirable to first move and then perform some I/O operation. In order to 364avoid clumsiness, most I/O routines can be preceded by the prefix 'mv' and 365the desired (y, x) coordinates prepended to the arguments to the function. For 366example, the calls 367 368<PRE> 369 move(y, x); 370 addch(ch); 371</PRE> 372 373can be replaced by 374 375<PRE> 376 mvaddch(y, x, ch); 377</PRE> 378 379and 380 381<PRE> 382 wmove(win, y, x); 383 waddch(win, ch); 384</PRE> 385 386can be replaced by 387 388<PRE> 389 mvwaddch(win, y, x, ch); 390</PRE> 391 392Note that the window description pointer (win) comes before the added (y, x) 393coordinates. If a function requires a window pointer, it is always the first 394parameter passed. 395 396<H3><A NAME="variables">Variables</A></H3> 397 398The <CODE>curses</CODE> library sets some variables describing the terminal 399capabilities. 400 401<PRE> 402 type name description 403 ------------------------------------------------------------------ 404 int LINES number of lines on the terminal 405 int COLS number of columns on the terminal 406</PRE> 407 408The <CODE>curses.h</CODE> also introduces some <CODE>#define</CODE> constants and types 409of general usefulness: 410 411<DL> 412<DT> <CODE>bool</CODE> 413<DD> boolean type, actually a `char' (e.g., <CODE>bool doneit;</CODE>) 414<DT> <CODE>TRUE</CODE> 415<DD> boolean `true' flag (1). 416<DT> <CODE>FALSE</CODE> 417<DD> boolean `false' flag (0). 418<DT> <CODE>ERR</CODE> 419<DD> error flag returned by routines on a failure (-1). 420<DT> <CODE>OK</CODE> 421<DD> error flag returned by routines when things go right. 422</DL> 423 424<H2><A NAME="using">Using the Library</A></H2> 425 426Now we describe how to actually use the screen package. In it, we assume all 427updating, reading, etc. is applied to <CODE>stdscr</CODE>. These instructions will 428work on any window, providing you change the function names and parameters as 429mentioned above. <P> 430 431Here is a sample program to motivate the discussion: 432 433<PRE> 434#include <curses.h> 435#include <signal.h> 436 437static void finish(int sig); 438 439int 440main(int argc, char *argv[]) 441{ 442 int num = 0; 443 444 /* initialize your non-curses data structures here */ 445 446 (void) signal(SIGINT, finish); /* arrange interrupts to terminate */ 447 448 (void) initscr(); /* initialize the curses library */ 449 keypad(stdscr, TRUE); /* enable keyboard mapping */ 450 (void) nonl(); /* tell curses not to do NL->CR/NL on output */ 451 (void) cbreak(); /* take input chars one at a time, no wait for \n */ 452 (void) echo(); /* echo input - in color */ 453 454 if (has_colors()) 455 { 456 start_color(); 457 458 /* 459 * Simple color assignment, often all we need. Color pair 0 cannot 460 * be redefined. This example uses the same value for the color 461 * pair as for the foreground color, though of course that is not 462 * necessary: 463 */ 464 init_pair(1, COLOR_RED, COLOR_BLACK); 465 init_pair(2, COLOR_GREEN, COLOR_BLACK); 466 init_pair(3, COLOR_YELLOW, COLOR_BLACK); 467 init_pair(4, COLOR_BLUE, COLOR_BLACK); 468 init_pair(5, COLOR_CYAN, COLOR_BLACK); 469 init_pair(6, COLOR_MAGENTA, COLOR_BLACK); 470 init_pair(7, COLOR_WHITE, COLOR_BLACK); 471 } 472 473 for (;;) 474 { 475 int c = getch(); /* refresh, accept single keystroke of input */ 476 attrset(COLOR_PAIR(num % 8)); 477 num++; 478 479 /* process the command keystroke */ 480 } 481 482 finish(0); /* we're done */ 483} 484 485static void finish(int sig) 486{ 487 endwin(); 488 489 /* do your non-curses wrapup here */ 490 491 exit(0); 492} 493</PRE> 494 495<H3><A NAME="starting">Starting up</A></H3> 496 497In order to use the screen package, the routines must know about terminal 498characteristics, and the space for <CODE>curscr</CODE> and <CODE>stdscr</CODE> must be 499allocated. These function <CODE>initscr()</CODE> does both these things. Since it 500must allocate space for the windows, it can overflow memory when attempting to 501do so. On the rare occasions this happens, <CODE>initscr()</CODE> will terminate 502the program with an error message. <CODE>initscr()</CODE> must always be called 503before any of the routines which affect windows are used. If it is not, the 504program will core dump as soon as either <CODE>curscr</CODE> or <CODE>stdscr</CODE> are 505referenced. However, it is usually best to wait to call it until after you are 506sure you will need it, like after checking for startup errors. Terminal status 507changing routines like <CODE>nl()</CODE> and <CODE>cbreak()</CODE> should be called 508after <CODE>initscr()</CODE>. <P> 509 510Once the screen windows have been allocated, you can set them up for 511your program. If you want to, say, allow a screen to scroll, use 512<CODE>scrollok()</CODE>. If you want the cursor to be left in place after 513the last change, use <CODE>leaveok()</CODE>. If this isn't done, 514<CODE>refresh()</CODE> will move the cursor to the window's current (y, x) 515coordinates after updating it. <P> 516 517You can create new windows of your own using the functions <CODE>newwin()</CODE>, 518<CODE>derwin()</CODE>, and <CODE>subwin()</CODE>. The routine <CODE>delwin()</CODE> will 519allow you to get rid of old windows. All the options described above can be 520applied to any window. 521 522<H3><A NAME="output">Output</A></H3> 523 524Now that we have set things up, we will want to actually update the terminal. 525The basic functions used to change what will go on a window are 526<CODE>addch()</CODE> and <CODE>move()</CODE>. <CODE>addch()</CODE> adds a character at the 527current (y, x) coordinates. <CODE>move()</CODE> changes the current (y, x) 528coordinates to whatever you want them to be. It returns <CODE>ERR</CODE> if you 529try to move off the window. As mentioned above, you can combine the two into 530<CODE>mvaddch()</CODE> to do both things at once. <P> 531 532The other output functions, such as <CODE>addstr()</CODE> and <CODE>printw()</CODE>, 533all call <CODE>addch()</CODE> to add characters to the window. <P> 534 535After you have put on the window what you want there, when you want the portion 536of the terminal covered by the window to be made to look like it, you must call 537<CODE>refresh()</CODE>. In order to optimize finding changes, <CODE>refresh()</CODE> 538assumes that any part of the window not changed since the last 539<CODE>refresh()</CODE> of that window has not been changed on the terminal, i.e., 540that you have not refreshed a portion of the terminal with an overlapping 541window. If this is not the case, the routine <CODE>touchwin()</CODE> is provided 542to make it look like the entire window has been changed, thus making 543<CODE>refresh()</CODE> check the whole subsection of the terminal for changes. <P> 544 545If you call <CODE>wrefresh()</CODE> with <CODE>curscr</CODE> as its argument, it will 546make the screen look like <CODE>curscr</CODE> thinks it looks like. This is useful 547for implementing a command which would redraw the screen in case it get messed 548up. 549 550<H3><A NAME="input">Input</A></H3> 551 552The complementary function to <CODE>addch()</CODE> is <CODE>getch()</CODE> which, if 553echo is set, will call <CODE>addch()</CODE> to echo the character. Since the 554screen package needs to know what is on the terminal at all times, if 555characters are to be echoed, the tty must be in raw or cbreak mode. Since 556initially the terminal has echoing enabled and is in ordinary ``cooked'' mode, 557one or the other has to changed before calling <CODE>getch()</CODE>; otherwise, 558the program's output will be unpredictable. <P> 559 560When you need to accept line-oriented input in a window, the functions 561<CODE>wgetstr()</CODE> and friends are available. There is even a <CODE>wscanw()</CODE> 562function that can do <CODE>scanf()</CODE>(3)-style multi-field parsing on window 563input. These pseudo-line-oriented functions turn on echoing while they 564execute. <P> 565 566The example code above uses the call <CODE>keypad(stdscr, TRUE)</CODE> to enable 567support for function-key mapping. With this feature, the <CODE>getch()</CODE> code 568watches the input stream for character sequences that correspond to arrow and 569function keys. These sequences are returned as pseudo-character values. The 570<CODE>#define</CODE> values returned are listed in the <CODE>curses.h</CODE> The 571mapping from sequences to <CODE>#define</CODE> values is determined by 572<CODE>key_</CODE> capabilities in the terminal's terminfo entry. 573 574<H3><A NAME="formschars">Using Forms Characters</A></H3> 575 576The <CODE>addch()</CODE> function (and some others, including <CODE>box()</CODE> and 577<CODE>border()</CODE>) can accept some pseudo-character arguments which are specially 578defined by <CODE>ncurses</CODE>. These are <CODE>#define</CODE> values set up in 579the <CODE>curses.h</CODE> header; see there for a complete list (look for 580the prefix <CODE>ACS_</CODE>). <P> 581 582The most useful of the ACS defines are the forms-drawing characters. You can 583use these to draw boxes and simple graphs on the screen. If the terminal 584does not have such characters, <CODE>curses.h</CODE> will map them to a 585recognizable (though ugly) set of ASCII defaults. 586 587<H3><A NAME="attributes">Character Attributes and Color</A></H3> 588 589The <CODE>ncurses</CODE> package supports screen highlights including standout, 590reverse-video, underline, and blink. It also supports color, which is treated 591as another kind of highlight. <P> 592 593Highlights are encoded, internally, as high bits of the pseudo-character type 594(<CODE>chtype</CODE>) that <CODE>curses.h</CODE> uses to represent the contents of a 595screen cell. See the <CODE>curses.h</CODE> header file for a complete list of 596highlight mask values (look for the prefix <CODE>A_</CODE>).<P> 597 598There are two ways to make highlights. One is to logical-or the value of the 599highlights you want into the character argument of an <CODE>addch()</CODE> call, 600or any other output call that takes a <CODE>chtype</CODE> argument. <P> 601 602The other is to set the current-highlight value. This is logical-or'ed with 603any highlight you specify the first way. You do this with the functions 604<CODE>attron()</CODE>, <CODE>attroff()</CODE>, and <CODE>attrset()</CODE>; see the manual 605pages for details. 606 607Color is a special kind of highlight. The package actually thinks in terms 608of color pairs, combinations of foreground and background colors. The sample 609code above sets up eight color pairs, all of the guaranteed-available colors 610on black. Note that each color pair is, in effect, given the name of its 611foreground color. Any other range of eight non-conflicting values could 612have been used as the first arguments of the <CODE>init_pair()</CODE> values. <P> 613 614Once you've done an <CODE>init_pair()</CODE> that creates color-pair N, you can 615use <CODE>COLOR_PAIR(N)</CODE> as a highlight that invokes that particular 616color combination. Note that <CODE>COLOR_PAIR(N)</CODE>, for constant N, 617is itself a compile-time constant and can be used in initializers. 618 619<H3><A NAME="mouse">Mouse Interfacing</A></H3> 620 621The <CODE>ncurses</CODE> library also provides a mouse interface. 622<!-- The 'note' tag is not portable enough --> 623<blockquote> 624<strong>NOTE:</strong> this facility is specific to <CODE>ncurses</CODE>, it is not part of either 625the XSI Curses standard, nor of System V Release 4, nor BSD curses. 626System V Release 4 curses contains code with similar interface definitions, 627however it is not documented. Other than by disassembling the library, we 628have no way to determine exactly how that mouse code works. 629Thus, we recommend that you wrap mouse-related code in an #ifdef using the 630feature macro NCURSES_MOUSE_VERSION so it will not be compiled and linked 631on non-ncurses systems. 632</blockquote> 633 634Presently, mouse event reporting works in the following environments: 635<ul> 636<li>xterm and similar programs such as rxvt. 637<li>Linux console, when configured with <CODE>gpm</CODE>(1), Alessandro 638Rubini's mouse server. 639<li>FreeBSD sysmouse (console) 640<li>OS/2 EMX 641</ul> 642<P> 643The mouse interface is very simple. To activate it, you use the function 644<CODE>mousemask()</CODE>, passing it as first argument a bit-mask that specifies 645what kinds of events you want your program to be able to see. It will 646return the bit-mask of events that actually become visible, which may differ 647from the argument if the mouse device is not capable of reporting some of 648the event types you specify. <P> 649 650Once the mouse is active, your application's command loop should watch 651for a return value of <CODE>KEY_MOUSE</CODE> from <CODE>wgetch()</CODE>. When 652you see this, a mouse event report has been queued. To pick it off 653the queue, use the function <CODE>getmouse()</CODE> (you must do this before 654the next <CODE>wgetch()</CODE>, otherwise another mouse event might come 655in and make the first one inaccessible). <P> 656 657Each call to <CODE>getmouse()</CODE> fills a structure (the address of which you'll 658pass it) with mouse event data. The event data includes zero-origin, 659screen-relative character-cell coordinates of the mouse pointer. It also 660includes an event mask. Bits in this mask will be set, corresponding 661to the event type being reported. <P> 662 663The mouse structure contains two additional fields which may be 664significant in the future as ncurses interfaces to new kinds of 665pointing device. In addition to x and y coordinates, there is a slot 666for a z coordinate; this might be useful with touch-screens that can 667return a pressure or duration parameter. There is also a device ID 668field, which could be used to distinguish between multiple pointing 669devices. <P> 670 671The class of visible events may be changed at any time via <CODE>mousemask()</CODE>. 672Events that can be reported include presses, releases, single-, double- and 673triple-clicks (you can set the maximum button-down time for clicks). If 674you don't make clicks visible, they will be reported as press-release 675pairs. In some environments, the event mask may include bits reporting 676the state of shift, alt, and ctrl keys on the keyboard during the event. <P> 677 678A function to check whether a mouse event fell within a given window is 679also supplied. You can use this to see whether a given window should 680consider a mouse event relevant to it. <P> 681 682Because mouse event reporting will not be available in all 683environments, it would be unwise to build <CODE>ncurses</CODE> 684applications that <EM>require</EM> the use of a mouse. Rather, you should 685use the mouse as a shortcut for point-and-shoot commands your application 686would normally accept from the keyboard. Two of the test games in the 687<CODE>ncurses</CODE> distribution (<CODE>bs</CODE> and <CODE>knight</CODE>) contain 688code that illustrates how this can be done. <P> 689 690See the manual page <CODE>curs_mouse(3X)</CODE> for full details of the 691mouse-interface functions. 692 693<H3><A NAME="finishing">Finishing Up</A></H3> 694 695In order to clean up after the <CODE>ncurses</CODE> routines, the routine 696<CODE>endwin()</CODE> is provided. It restores tty modes to what they were when 697<CODE>initscr()</CODE> was first called, and moves the cursor down to the 698lower-left corner. Thus, anytime after the call to initscr, <CODE>endwin()</CODE> 699should be called before exiting. 700 701<H2><A NAME="functions">Function Descriptions</A></H2> 702 703We describe the detailed behavior of some important curses functions here, as a 704supplement to the manual page descriptions. 705 706<H3><A NAME="init">Initialization and Wrapup</A></H3> 707 708<DL> 709<DT> <CODE>initscr()</CODE> 710<DD> The first function called should almost always be <CODE>initscr()</CODE>. 711This will determine the terminal type and 712initialize curses data structures. <CODE>initscr()</CODE> also arranges that 713the first call to <CODE>refresh()</CODE> will clear the screen. If an error 714occurs a message is written to standard error and the program 715exits. Otherwise it returns a pointer to stdscr. A few functions may be 716called before initscr (<CODE>slk_init()</CODE>, <CODE>filter()</CODE>, 717<CODE>ripoffline()</CODE>, <CODE>use_env()</CODE>, and, if you are using multiple 718terminals, <CODE>newterm()</CODE>.) 719<DT> <CODE>endwin()</CODE> 720<DD> Your program should always call <CODE>endwin()</CODE> before exiting or 721shelling out of the program. This function will restore tty modes, 722move the cursor to the lower left corner of the screen, reset the 723terminal into the proper non-visual mode. Calling <CODE>refresh()</CODE> 724or <CODE>doupdate()</CODE> after a temporary escape from the program will 725restore the ncurses screen from before the escape. 726<DT> <CODE>newterm(type, ofp, ifp)</CODE> 727<DD> A program which outputs to more than one terminal should use 728<CODE>newterm()</CODE> instead of <CODE>initscr()</CODE>. <CODE>newterm()</CODE> should 729be called once for each terminal. It returns a variable of type 730<CODE>SCREEN *</CODE> which should be saved as a reference to that 731terminal. 732(NOTE: a SCREEN variable is not a <em>screen</em> in the sense we 733are describing in this introduction, but a collection of 734parameters used to assist in optimizing the display.) 735The arguments are the type of the terminal (a string) and 736<CODE>FILE</CODE> pointers for the output and input of the terminal. If 737type is NULL then the environment variable <CODE>$TERM</CODE> is used. 738<CODE>endwin()</CODE> should called once at wrapup time for each terminal 739opened using this function. 740<DT> <CODE>set_term(new)</CODE> 741<DD> This function is used to switch to a different terminal previously 742opened by <CODE>newterm()</CODE>. The screen reference for the new terminal 743is passed as the parameter. The previous terminal is returned by the 744function. All other calls affect only the current terminal. 745<DT> <CODE>delscreen(sp)</CODE> 746<DD> The inverse of <CODE>newterm()</CODE>; deallocates the data structures 747associated with a given <CODE>SCREEN</CODE> reference. 748</DL> 749 750<H3><A NAME="flush">Causing Output to the Terminal</A></H3> 751 752<DL> 753<DT> <CODE>refresh()</CODE> and <CODE>wrefresh(win)</CODE> 754<DD> These functions must be called to actually get any output on 755the terminal, as other routines merely manipulate data 756structures. <CODE>wrefresh()</CODE> copies the named window to the physical 757terminal screen, taking into account what is already 758there in order to do optimizations. <CODE>refresh()</CODE> does a 759refresh of <CODE>stdscr</CODE>. Unless <CODE>leaveok()</CODE> has been 760enabled, the physical cursor of the terminal is left at the 761location of the window's cursor. 762<DT> <CODE>doupdate()</CODE> and <CODE>wnoutrefresh(win)</CODE> 763<DD> These two functions allow multiple updates with more efficiency 764than wrefresh. To use them, it is important to understand how curses 765works. In addition to all the window structures, curses keeps two 766data structures representing the terminal screen: a physical screen, 767describing what is actually on the screen, and a virtual screen, 768describing what the programmer wants to have on the screen. wrefresh 769works by first copying the named window to the virtual screen 770(<CODE>wnoutrefresh()</CODE>), and then calling the routine to update the 771screen (<CODE>doupdate()</CODE>). If the programmer wishes to output 772several windows at once, a series of calls to <CODE>wrefresh</CODE> will result 773in alternating calls to <CODE>wnoutrefresh()</CODE> and <CODE>doupdate()</CODE>, 774causing several bursts of output to the screen. By calling 775<CODE>wnoutrefresh()</CODE> for each window, it is then possible to call 776<CODE>doupdate()</CODE> once, resulting in only one burst of output, with 777fewer total characters transmitted (this also avoids a visually annoying 778flicker at each update). 779</DL> 780 781<H3><A NAME="lowlevel">Low-Level Capability Access</A></H3> 782 783<DL> 784<DT> <CODE>setupterm(term, filenum, errret)</CODE> 785<DD> This routine is called to initialize a terminal's description, without setting 786up the curses screen structures or changing the tty-driver mode bits. 787<CODE>term</CODE> is the character string representing the name of the terminal 788being used. <CODE>filenum</CODE> is the UNIX file descriptor of the terminal to 789be used for output. <CODE>errret</CODE> is a pointer to an integer, in which a 790success or failure indication is returned. The values returned can be 1 (all 791is well), 0 (no such terminal), or -1 (some problem locating the terminfo 792database). <P> 793 794The value of <CODE>term</CODE> can be given as NULL, which will cause the value of 795<CODE>TERM</CODE> in the environment to be used. The <CODE>errret</CODE> pointer can 796also be given as NULL, meaning no error code is wanted. If <CODE>errret</CODE> is 797defaulted, and something goes wrong, <CODE>setupterm()</CODE> will print an 798appropriate error message and exit, rather than returning. Thus, a simple 799program can call setupterm(0, 1, 0) and not worry about initialization 800errors. <P> 801 802After the call to <CODE>setupterm()</CODE>, the global variable <CODE>cur_term</CODE> is 803set to point to the current structure of terminal capabilities. By calling 804<CODE>setupterm()</CODE> for each terminal, and saving and restoring 805<CODE>cur_term</CODE>, it is possible for a program to use two or more terminals at 806once. <CODE>Setupterm()</CODE> also stores the names section of the terminal 807description in the global character array <CODE>ttytype[]</CODE>. Subsequent calls 808to <CODE>setupterm()</CODE> will overwrite this array, so you'll have to save it 809yourself if need be. 810</DL> 811 812<H3><A NAME="debugging">Debugging</A></H3> 813 814<!-- The 'note' tag is not portable enough --> 815<blockquote> 816<strong>NOTE:</strong> These functions are not part of the standard curses API! 817</blockquote> 818 819<DL> 820<DT> <CODE>trace()</CODE> 821<DD> 822This function can be used to explicitly set a trace level. If the 823trace level is nonzero, execution of your program will generate a file 824called `trace' in the current working directory containing a report on 825the library's actions. Higher trace levels enable more detailed (and 826verbose) reporting -- see comments attached to <CODE>TRACE_</CODE> defines 827in the <CODE>curses.h</CODE> file for details. (It is also possible to set 828a trace level by assigning a trace level value to the environment variable 829<CODE>NCURSES_TRACE</CODE>). 830<DT> <CODE>_tracef()</CODE> 831<DD> 832This function can be used to output your own debugging information. It is only 833available only if you link with -lncurses_g. It can be used the same way as 834<CODE>printf()</CODE>, only it outputs a newline after the end of arguments. 835The output goes to a file called <CODE>trace</CODE> in the current directory. 836</DL> 837 838Trace logs can be difficult to interpret due to the sheer volume of 839data dumped in them. There is a script called <STRONG>tracemunch</STRONG> 840included with the <CODE>ncurses</CODE> distribution that can alleviate 841this problem somewhat; it compacts long sequences of similar operations into 842more succinct single-line pseudo-operations. These pseudo-ops can be 843distinguished by the fact that they are named in capital letters. 844 845<H2><A NAME="hints">Hints, Tips, and Tricks</A></H2> 846 847The <CODE>ncurses</CODE> manual pages are a complete reference for this library. 848In the remainder of this document, we discuss various useful methods that 849may not be obvious from the manual page descriptions. 850 851<H3><A NAME="caution">Some Notes of Caution</A></H3> 852 853If you find yourself thinking you need to use <CODE>noraw()</CODE> or 854<CODE>nocbreak()</CODE>, think again and move carefully. It's probably 855better design to use <CODE>getstr()</CODE> or one of its relatives to 856simulate cooked mode. The <CODE>noraw()</CODE> and <CODE>nocbreak()</CODE> 857functions try to restore cooked mode, but they may end up clobbering 858some control bits set before you started your application. Also, they 859have always been poorly documented, and are likely to hurt your 860application's usability with other curses libraries. <P> 861 862Bear in mind that <CODE>refresh()</CODE> is a synonym for <CODE>wrefresh(stdscr)</CODE>. 863Don't try to mix use of <CODE>stdscr</CODE> with use of windows declared 864by <CODE>newwin()</CODE>; a <CODE>refresh()</CODE> call will blow them off the 865screen. The right way to handle this is to use <CODE>subwin()</CODE>, or 866not touch <CODE>stdscr</CODE> at all and tile your screen with declared 867windows which you then <CODE>wnoutrefresh()</CODE> somewhere in your program 868event loop, with a single <CODE>doupdate()</CODE> call to trigger actual 869repainting. <P> 870 871You are much less likely to run into problems if you design your screen 872layouts to use tiled rather than overlapping windows. Historically, 873curses support for overlapping windows has been weak, fragile, and poorly 874documented. The <CODE>ncurses</CODE> library is not yet an exception to this 875rule. <P> 876 877There is a panels library included in the <CODE>ncurses</CODE> 878distribution that does a pretty good job of strengthening the 879overlapping-windows facilities. <P> 880 881Try to avoid using the global variables LINES and COLS. Use 882<CODE>getmaxyx()</CODE> on the <CODE>stdscr</CODE> context instead. Reason: 883your code may be ported to run in an environment with window resizes, 884in which case several screens could be open with different sizes. 885 886<H3><A NAME="leaving">Temporarily Leaving NCURSES Mode</A></H3> 887 888Sometimes you will want to write a program that spends most of its time in 889screen mode, but occasionally returns to ordinary `cooked' mode. A common 890reason for this is to support shell-out. This behavior is simple to arrange 891in <CODE>ncurses</CODE>. <P> 892 893To leave <CODE>ncurses</CODE> mode, call <CODE>endwin()</CODE> as you would if you 894were intending to terminate the program. This will take the screen back to 895cooked mode; you can do your shell-out. When you want to return to 896<CODE>ncurses</CODE> mode, simply call <CODE>refresh()</CODE> or <CODE>doupdate()</CODE>. 897This will repaint the screen. <P> 898 899There is a boolean function, <CODE>isendwin()</CODE>, which code can use to 900test whether <CODE>ncurses</CODE> screen mode is active. It returns <CODE>TRUE</CODE> 901in the interval between an <CODE>endwin()</CODE> call and the following 902<CODE>refresh()</CODE>, <CODE>FALSE</CODE> otherwise. <P> 903 904Here is some sample code for shellout: 905 906<PRE> 907 addstr("Shelling out..."); 908 def_prog_mode(); /* save current tty modes */ 909 endwin(); /* restore original tty modes */ 910 system("sh"); /* run shell */ 911 addstr("returned.\n"); /* prepare return message */ 912 refresh(); /* restore save modes, repaint screen */ 913</PRE> 914 915<H3><A NAME="xterm">Using NCURSES under XTERM</A></H3> 916 917A resize operation in X sends <CODE>SIGWINCH</CODE> to the application running 918under xterm. 919 920The easiest way to handle <CODE>SIGWINCH</CODE> 921is to do an <CODE>endwin</CODE>, 922followed by an <CODE>refresh</CODE> and a screen repaint you code 923yourself. 924The <CODE>refresh</CODE> will pick up the new screen size from the 925xterm's environment. <P> 926 927That is the standard way, of course (it even works with some vendor's curses 928implementations). 929Its drawback is that it clears the screen to reinitialize the display, and does 930not resize subwindows which must be shrunk. 931<CODE>Ncurses</CODE> provides an extension which works better, the 932<CODE>resizeterm</CODE> function. That function ensures that all windows 933are limited to the new screen dimensions, and pads <CODE>stdscr</CODE> 934with blanks if the screen is larger. <P> 935 936The <CODE>ncurses</CODE> library provides a SIGWINCH signal handler, 937which pushes a <CODE>KEY_RESIZE</CODE> via the wgetch() calls. 938When <CODE>ncurses</CODE> returns that code, 939it calls <code>resizeterm</CODE> 940to update the size of the standard screen's window, repainting that 941(filling with blanks or truncating as needed). 942It also resizes other windows, 943but its effect may be less satisfactory because it cannot 944know how you want the screen re-painted. 945You will usually have to write special-purpose code to handle 946<CODE>KEY_RESIZE</CODE> yourself. 947 948<H3><A NAME="screens">Handling Multiple Terminal Screens</A></H3> 949 950The <CODE>initscr()</CODE> function actually calls a function named 951<CODE>newterm()</CODE> to do most of its work. If you are writing a program that 952opens multiple terminals, use <CODE>newterm()</CODE> directly. <P> 953 954For each call, you will have to specify a terminal type and a pair of file 955pointers; each call will return a screen reference, and <CODE>stdscr</CODE> will be 956set to the last one allocated. You will switch between screens with the 957<CODE>set_term</CODE> call. Note that you will also have to call 958<CODE>def_shell_mode</CODE> and <CODE>def_prog_mode</CODE> on each tty yourself. 959 960<H3><A NAME="testing">Testing for Terminal Capabilities</A></H3> 961 962Sometimes you may want to write programs that test for the presence of various 963capabilities before deciding whether to go into <CODE>ncurses</CODE> mode. An easy 964way to do this is to call <CODE>setupterm()</CODE>, then use the functions 965<CODE>tigetflag()</CODE>, <CODE>tigetnum()</CODE>, and <CODE>tigetstr()</CODE> to do your 966testing. <P> 967 968A particularly useful case of this often comes up when you want to 969test whether a given terminal type should be treated as `smart' 970(cursor-addressable) or `stupid'. The right way to test this is to see 971if the return value of <CODE>tigetstr("cup")</CODE> is non-NULL. Alternatively, 972you can include the <CODE>term.h</CODE> file and test the value of the 973macro <CODE>cursor_address</CODE>. 974 975<H3><A NAME="tuning">Tuning for Speed</A></H3> 976 977Use the <CODE>addchstr()</CODE> family of functions for fast 978screen-painting of text when you know the text doesn't contain any 979control characters. Try to make attribute changes infrequent on your 980screens. Don't use the <CODE>immedok()</CODE> option! 981 982<H3><A NAME="special">Special Features of NCURSES</A></H3> 983 984The <CODE>wresize()</CODE> function allows you to resize a window in place. 985The associated <CODE>resizeterm()</CODE> function simplifies the construction 986of <a HREF="#xterm">SIGWINCH</a> handlers, for resizing all windows. <P> 987 988The <CODE>define_key()</CODE> function allows you 989to define at runtime function-key control sequences which are not in the 990terminal description. 991The <CODE>keyok()</CODE> function allows you to temporarily 992enable or disable interpretation of any function-key control sequence. <P> 993 994The <CODE>use_default_colors()</CODE> function allows you to construct 995applications which can use the terminal's default foreground and 996background colors as an additional "default" color. 997Several terminal emulators support this feature, which is based on ISO 6429. <P> 998 999Ncurses supports up 16 colors, unlike SVr4 curses which defines only 8. 1000While most terminals which provide color allow only 8 colors, about 1001a quarter (including XFree86 xterm) support 16 colors. 1002 1003<H2><A NAME="compat">Compatibility with Older Versions</A></H2> 1004 1005Despite our best efforts, there are some differences between <CODE>ncurses</CODE> 1006and the (undocumented!) behavior of older curses implementations. These arise 1007from ambiguities or omissions in the documentation of the API. 1008 1009<H3><A NAME="refbug">Refresh of Overlapping Windows</A></H3> 1010 1011If you define two windows A and B that overlap, and then alternately scribble 1012on and refresh them, the changes made to the overlapping region under historic 1013<CODE>curses</CODE> versions were often not documented precisely. <P> 1014 1015To understand why this is a problem, remember that screen updates are 1016calculated between two representations of the <EM>entire</EM> display. The 1017documentation says that when you refresh a window, it is first copied to the 1018virtual screen, and then changes are calculated to update the physical screen 1019(and applied to the terminal). But "copied to" is not very specific, and 1020subtle differences in how copying works can produce different behaviors in the 1021case where two overlapping windows are each being refreshed at unpredictable 1022intervals. <P> 1023 1024What happens to the overlapping region depends on what <CODE>wnoutrefresh()</CODE> 1025does with its argument -- what portions of the argument window it copies to the 1026virtual screen. Some implementations do "change copy", copying down only 1027locations in the window that have changed (or been marked changed with 1028<CODE>wtouchln()</CODE> and friends). Some implementations do "entire copy", 1029copying <EM>all</EM> window locations to the virtual screen whether or not 1030they have changed. <P> 1031 1032The <CODE>ncurses</CODE> library itself has not always been consistent on this 1033score. Due to a bug, versions 1.8.7 to 1.9.8a did entire copy. Versions 10341.8.6 and older, and versions 1.9.9 and newer, do change copy. <P> 1035 1036For most commercial curses implementations, it is not documented and not known 1037for sure (at least not to the <CODE>ncurses</CODE> maintainers) whether they do 1038change copy or entire copy. We know that System V release 3 curses has logic 1039in it that looks like an attempt to do change copy, but the surrounding logic 1040and data representations are sufficiently complex, and our knowledge 1041sufficiently indirect, that it's hard to know whether this is reliable. 1042 1043It is not clear what the SVr4 documentation and XSI standard intend. The XSI 1044Curses standard barely mentions wnoutrefresh(); the SVr4 documents seem to be 1045describing entire-copy, but it is possible with some effort and straining to 1046read them the other way. <P> 1047 1048It might therefore be unwise to rely on either behavior in programs that might 1049have to be linked with other curses implementations. Instead, you can do an 1050explicit <CODE>touchwin()</CODE> before the <CODE>wnoutrefresh()</CODE> call to 1051guarantee an entire-contents copy anywhere. <P> 1052 1053The really clean way to handle this is to use the panels library. If, 1054when you want a screen update, you do <CODE>update_panels()</CODE>, it will 1055do all the necessary <CODE>wnoutrefresh()</CODE> calls for whatever panel 1056stacking order you have defined. Then you can do one <CODE>doupdate()</CODE> 1057and there will be a <EM>single</EM> burst of physical I/O that will do 1058all your updates. 1059 1060<H3><A NAME="backbug">Background Erase</A></H3> 1061 1062If you have been using a very old versions of <CODE>ncurses</CODE> (1.8.7 or 1063older) you may be surprised by the behavior of the erase functions. In older 1064versions, erased areas of a window were filled with a blank modified by the 1065window's current attribute (as set by <STRONG>wattrset()</STRONG>, <STRONG>wattron()</STRONG>, 1066<STRONG>wattroff()</STRONG> and friends). <P> 1067 1068In newer versions, this is not so. Instead, the attribute of erased blanks 1069is normal unless and until it is modified by the functions <CODE>bkgdset()</CODE> 1070or <CODE>wbkgdset()</CODE>. <P> 1071 1072This change in behavior conforms <CODE>ncurses</CODE> to System V Release 4 and 1073the XSI Curses standard. 1074 1075<H2><A NAME="xsifuncs">XSI Curses Conformance</A></H2> 1076 1077The <CODE>ncurses</CODE> library is intended to be base-level conformant with the 1078XSI Curses standard from X/Open. Many extended-level features (in fact, almost 1079all features not directly concerned with wide characters and 1080internationalization) are also supported. <P> 1081 1082One effect of XSI conformance is the change in behavior described under 1083<A HREF="#backbug">"Background Erase -- Compatibility with Old Versions"</A>. <P> 1084 1085Also, <CODE>ncurses</CODE> meets the XSI requirement that every macro 1086entry point have a corresponding function which may be linked (and 1087will be prototype-checked) if the macro definition is disabled with 1088<CODE>#undef</CODE>. 1089 1090<H1><A NAME="panels">The Panels Library</A></H1> 1091 1092The <CODE>ncurses</CODE> library by itself provides good support for screen 1093displays in which the windows are tiled (non-overlapping). In the more 1094general case that windows may overlap, you have to use a series of 1095<CODE>wnoutrefresh()</CODE> calls followed by a <CODE>doupdate()</CODE>, and be 1096careful about the order you do the window refreshes in. It has to be 1097bottom-upwards, otherwise parts of windows that should be obscured will 1098show through. <P> 1099 1100When your interface design is such that windows may dive deeper into the 1101visibility stack or pop to the top at runtime, the resulting book-keeping 1102can be tedious and difficult to get right. Hence the panels library. <P> 1103 1104The <CODE>panel</CODE> library first appeared in AT&T System V. The 1105version documented here is the <CODE>panel</CODE> code distributed 1106with <CODE>ncurses</CODE>. 1107 1108<H2><A NAME="pcompile">Compiling With the Panels Library</A></H2> 1109 1110Your panels-using modules must import the panels library declarations with 1111 1112<PRE> 1113 #include <panel.h> 1114</PRE> 1115 1116and must be linked explicitly with the panels library using an 1117<CODE>-lpanel</CODE> argument. Note that they must also link the 1118<CODE>ncurses</CODE> library with <CODE>-lncurses</CODE>. Many linkers 1119are two-pass and will accept either order, but it is still good practice 1120to put <CODE>-lpanel</CODE> first and <CODE>-lncurses</CODE> second. 1121 1122<H2><A NAME="poverview">Overview of Panels</A></H2> 1123 1124A panel object is a window that is implicitly treated as part of a 1125<DFN>deck</DFN> including all other panel objects. The deck has an implicit 1126bottom-to-top visibility order. The panels library includes an update 1127function (analogous to <CODE>refresh()</CODE>) that displays all panels in the 1128deck in the proper order to resolve overlaps. The standard window, 1129<CODE>stdscr</CODE>, is considered below all panels. <P> 1130 1131Details on the panels functions are available in the man pages. We'll just 1132hit the highlights here. <P> 1133 1134You create a panel from a window by calling <CODE>new_panel()</CODE> on a 1135window pointer. It then becomes the top of the deck. The panel's window 1136is available as the value of <CODE>panel_window()</CODE> called with the 1137panel pointer as argument.<P> 1138 1139You can delete a panel (removing it from the deck) with <CODE>del_panel</CODE>. 1140This will not deallocate the associated window; you have to do that yourself. 1141 1142You can replace a panel's window with a different window by calling 1143<CODE>replace_window</CODE>. The new window may be of different size; 1144the panel code will re-compute all overlaps. This operation doesn't 1145change the panel's position in the deck. <P> 1146 1147To move a panel's window, use <CODE>move_panel()</CODE>. The 1148<CODE>mvwin()</CODE> function on the panel's window isn't sufficient because it 1149doesn't update the panels library's representation of where the windows are. 1150This operation leaves the panel's depth, contents, and size unchanged. <P> 1151 1152Two functions (<CODE>top_panel()</CODE>, <CODE>bottom_panel()</CODE>) are 1153provided for rearranging the deck. The first pops its argument window to the 1154top of the deck; the second sends it to the bottom. Either operation leaves 1155the panel's screen location, contents, and size unchanged. <P> 1156 1157The function <CODE>update_panels()</CODE> does all the 1158<CODE>wnoutrefresh()</CODE> calls needed to prepare for 1159<CODE>doupdate()</CODE> (which you must call yourself, afterwards). <P> 1160 1161Typically, you will want to call <CODE>update_panels()</CODE> and 1162<CODE>doupdate()</CODE> just before accepting command input, once in each cycle 1163of interaction with the user. If you call <CODE>update_panels()</CODE> after 1164each and every panel write, you'll generate a lot of unnecessary refresh 1165activity and screen flicker. 1166 1167<H2><A NAME="pstdscr">Panels, Input, and the Standard Screen</A></H2> 1168 1169You shouldn't mix <CODE>wnoutrefresh()</CODE> or <CODE>wrefresh()</CODE> 1170operations with panels code; this will work only if the argument window 1171is either in the top panel or unobscured by any other panels. <P> 1172 1173The <CODE>stsdcr</CODE> window is a special case. It is considered below all 1174panels. Because changes to panels may obscure parts of <CODE>stdscr</CODE>, 1175though, you should call <CODE>update_panels()</CODE> before 1176<CODE>doupdate()</CODE> even when you only change <CODE>stdscr</CODE>. <P> 1177 1178Note that <CODE>wgetch</CODE> automatically calls <CODE>wrefresh</CODE>. 1179Therefore, before requesting input from a panel window, you need to be sure 1180that the panel is totally unobscured. <P> 1181 1182There is presently no way to display changes to one obscured panel without 1183repainting all panels. 1184 1185<H2><A NAME="hiding">Hiding Panels</A></H2> 1186 1187It's possible to remove a panel from the deck temporarily; use 1188<CODE>hide_panel</CODE> for this. Use <CODE>show_panel()</CODE> to render it 1189visible again. The predicate function <CODE>panel_hidden</CODE> 1190tests whether or not a panel is hidden. <P> 1191 1192The <CODE>panel_update</CODE> code ignores hidden panels. You cannot do 1193<CODE>top_panel()</CODE> or <CODE>bottom_panel</CODE> on a hidden panel(). 1194Other panels operations are applicable. 1195 1196<H2><A NAME="pmisc">Miscellaneous Other Facilities</A></H2> 1197 1198It's possible to navigate the deck using the functions 1199<CODE>panel_above()</CODE> and <CODE>panel_below</CODE>. Handed a panel 1200pointer, they return the panel above or below that panel. Handed 1201<CODE>NULL</CODE>, they return the bottom-most or top-most panel. <P> 1202 1203Every panel has an associated user pointer, not used by the panel code, to 1204which you can attach application data. See the man page documentation 1205of <CODE>set_panel_userptr()</CODE> and <CODE>panel_userptr</CODE> for 1206details. 1207 1208<H1><A NAME="menu">The Menu Library</A></H1> 1209 1210A menu is a screen display that assists the user to choose some subset 1211of a given set of items. The <CODE>menu</CODE> library is a curses 1212extension that supports easy programming of menu hierarchies with a 1213uniform but flexible interface. <P> 1214 1215The <CODE>menu</CODE> library first appeared in AT&T System V. The 1216version documented here is the <CODE>menu</CODE> code distributed 1217with <CODE>ncurses</CODE>. 1218 1219<H2><A NAME="mcompile">Compiling With the menu Library</A></H2> 1220 1221Your menu-using modules must import the menu library declarations with 1222 1223<PRE> 1224 #include <menu.h> 1225</PRE> 1226 1227and must be linked explicitly with the menus library using an 1228<CODE>-lmenu</CODE> argument. Note that they must also link the 1229<CODE>ncurses</CODE> library with <CODE>-lncurses</CODE>. Many linkers 1230are two-pass and will accept either order, but it is still good practice 1231to put <CODE>-lmenu</CODE> first and <CODE>-lncurses</CODE> second. 1232 1233<H2><A NAME="moverview">Overview of Menus</A></H2> 1234 1235The menus created by this library consist of collections of 1236<DFN>items</DFN> including a name string part and a description string 1237part. To make menus, you create groups of these items and connect 1238them with menu frame objects. <P> 1239 1240The menu can then by <DFN>posted</DFN>, that is written to an 1241associated window. Actually, each menu has two associated windows; a 1242containing window in which the programmer can scribble titles or 1243borders, and a subwindow in which the menu items proper are displayed. 1244If this subwindow is too small to display all the items, it will be a 1245scrollable viewport on the collection of items. <P> 1246 1247A menu may also be <DFN>unposted</DFN> (that is, undisplayed), and finally 1248freed to make the storage associated with it and its items available for 1249re-use. <P> 1250 1251The general flow of control of a menu program looks like this: 1252 1253<OL> 1254<LI>Initialize <CODE>curses</CODE>. 1255<LI>Create the menu items, using <CODE>new_item()</CODE>. 1256<LI>Create the menu using <CODE>new_menu()</CODE>. 1257<LI>Post the menu using <CODE>post_menu()</CODE>. 1258<LI>Refresh the screen. 1259<LI>Process user requests via an input loop. 1260<LI>Unpost the menu using <CODE>unpost_menu()</CODE>. 1261<LI>Free the menu, using <CODE>free_menu()</CODE>. 1262<LI>Free the items using <CODE>free_item()</CODE>. 1263<LI>Terminate <CODE>curses</CODE>. 1264</OL> 1265 1266<H2><A NAME="mselect">Selecting items</A></H2> 1267 1268Menus may be multi-valued or (the default) single-valued (see the manual 1269page <CODE>menu_opts(3x)</CODE> to see how to change the default). 1270Both types always have a <DFN>current item</DFN>. <P> 1271 1272From a single-valued menu you can read the selected value simply by looking 1273at the current item. From a multi-valued menu, you get the selected set 1274by looping through the items applying the <CODE>item_value()</CODE> 1275predicate function. Your menu-processing code can use the function 1276<CODE>set_item_value()</CODE> to flag the items in the select set. <P> 1277 1278Menu items can be made unselectable using <CODE>set_item_opts()</CODE> 1279or <CODE>item_opts_off()</CODE> with the <CODE>O_SELECTABLE</CODE> 1280argument. This is the only option so far defined for menus, but it 1281is good practice to code as though other option bits might be on. 1282 1283<H2><A NAME="mdisplay">Menu Display</A></H2> 1284 1285The menu library calculates a minimum display size for your window, based 1286on the following variables: 1287 1288<UL> 1289<LI>The number and maximum length of the menu items 1290<LI>Whether the O_ROWMAJOR option is enabled 1291<LI>Whether display of descriptions is enabled 1292<LI>Whatever menu format may have been set by the programmer 1293<LI>The length of the menu mark string used for highlighting selected items 1294</UL> 1295 1296The function <CODE>set_menu_format()</CODE> allows you to set the 1297maximum size of the viewport or <DFN>menu page</DFN> that will be used 1298to display menu items. You can retrieve any format associated with a 1299menu with <CODE>menu_format()</CODE>. The default format is rows=16, 1300columns=1. <P> 1301 1302The actual menu page may be smaller than the format size. This depends 1303on the item number and size and whether O_ROWMAJOR is on. This option 1304(on by default) causes menu items to be displayed in a `raster-scan' 1305pattern, so that if more than one item will fit horizontally the first 1306couple of items are side-by-side in the top row. The alternative is 1307column-major display, which tries to put the first several items in 1308the first column. <P> 1309 1310As mentioned above, a menu format not large enough to allow all items to fit 1311on-screen will result in a menu display that is vertically scrollable. <P> 1312You can scroll it with requests to the menu driver, which will be described 1313in the section on <A HREF="#minput">menu input handling</A>. <P> 1314 1315Each menu has a <DFN>mark string</DFN> used to visually tag selected items; 1316see the <CODE>menu_mark(3x)</CODE> manual page for details. The mark 1317string length also influences the menu page size. <P> 1318 1319The function <CODE>scale_menu()</CODE> returns the minimum display size 1320that the menu code computes from all these factors. 1321 1322There are other menu display attributes including a select attribute, 1323an attribute for selectable items, an attribute for unselectable items, 1324and a pad character used to separate item name text from description 1325text. These have reasonable defaults which the library allows you to 1326change (see the <CODE>menu_attribs(3x)</CODE> manual page. 1327 1328<H2><A NAME="mwindows">Menu Windows</A></H2> 1329 1330Each menu has, as mentioned previously, a pair of associated windows. 1331Both these windows are painted when the menu is posted and erased when 1332the menu is unposted. <P> 1333 1334The outer or frame window is not otherwise touched by the menu 1335routines. It exists so the programmer can associate a title, a 1336border, or perhaps help text with the menu and have it properly 1337refreshed or erased at post/unpost time. The inner window or 1338<DFN>subwindow</DFN> is where the current menu page is displayed. <P> 1339 1340By default, both windows are <CODE>stdscr</CODE>. You can set them with the 1341functions in <CODE>menu_win(3x)</CODE>. <P> 1342 1343When you call <CODE>post_menu()</CODE>, you write the menu to its 1344subwindow. When you call <CODE>unpost_menu()</CODE>, you erase the 1345subwindow, However, neither of these actually modifies the screen. To 1346do that, call <CODE>wrefresh()</CODE> or some equivalent. 1347 1348<H2><A NAME="minput">Processing Menu Input</A></H2> 1349 1350The main loop of your menu-processing code should call 1351<CODE>menu_driver()</CODE> repeatedly. The first argument of this routine 1352is a menu pointer; the second is a menu command code. You should write an 1353input-fetching routine that maps input characters to menu command codes, and 1354pass its output to <CODE>menu_driver()</CODE>. The menu command codes are 1355fully documented in <CODE>menu_driver(3x)</CODE>. <P> 1356 1357The simplest group of command codes is <CODE>REQ_NEXT_ITEM</CODE>, 1358<CODE>REQ_PREV_ITEM</CODE>, <CODE>REQ_FIRST_ITEM</CODE>, 1359<CODE>REQ_LAST_ITEM</CODE>, <CODE>REQ_UP_ITEM</CODE>, 1360<CODE>REQ_DOWN_ITEM</CODE>, <CODE>REQ_LEFT_ITEM</CODE>, 1361<CODE>REQ_RIGHT_ITEM</CODE>. These change the currently selected 1362item. These requests may cause scrolling of the menu page if it only 1363partially displayed. <P> 1364 1365There are explicit requests for scrolling which also change the 1366current item (because the select location does not change, but the 1367item there does). These are <CODE>REQ_SCR_DLINE</CODE>, 1368<CODE>REQ_SCR_ULINE</CODE>, <CODE>REQ_SCR_DPAGE</CODE>, and 1369<CODE>REQ_SCR_UPAGE</CODE>. <P> 1370 1371The <CODE>REQ_TOGGLE_ITEM</CODE> selects or deselects the current item. 1372It is for use in multi-valued menus; if you use it with <CODE>O_ONEVALUE</CODE> 1373on, you'll get an error return (<CODE>E_REQUEST_DENIED</CODE>). <P> 1374 1375Each menu has an associated pattern buffer. The 1376<CODE>menu_driver()</CODE> logic tries to accumulate printable ASCII 1377characters passed in in that buffer; when it matches a prefix of an 1378item name, that item (or the next matching item) is selected. If 1379appending a character yields no new match, that character is deleted 1380from the pattern buffer, and <CODE>menu_driver()</CODE> returns 1381<CODE>E_NO_MATCH</CODE>. <P> 1382 1383Some requests change the pattern buffer directly: 1384<CODE>REQ_CLEAR_PATTERN</CODE>, <CODE>REQ_BACK_PATTERN</CODE>, 1385<CODE>REQ_NEXT_MATCH</CODE>, <CODE>REQ_PREV_MATCH</CODE>. The latter 1386two are useful when pattern buffer input matches more than one item 1387in a multi-valued menu. <P> 1388 1389Each successful scroll or item navigation request clears the pattern 1390buffer. It is also possible to set the pattern buffer explicitly 1391with <CODE>set_menu_pattern()</CODE>. <P> 1392 1393Finally, menu driver requests above the constant <CODE>MAX_COMMAND</CODE> 1394are considered application-specific commands. The <CODE>menu_driver()</CODE> 1395code ignores them and returns <CODE>E_UNKNOWN_COMMAND</CODE>. 1396 1397<H2><A NAME="mmisc">Miscellaneous Other Features</A></H2> 1398 1399Various menu options can affect the processing and visual appearance 1400and input processing of menus. See <CODE>menu_opts(3x) for 1401details.</CODE> <P> 1402 1403It is possible to change the current item from application code; this 1404is useful if you want to write your own navigation requests. It is 1405also possible to explicitly set the top row of the menu display. See 1406<CODE>mitem_current(3x)</CODE>. 1407 1408If your application needs to change the menu subwindow cursor for 1409any reason, <CODE>pos_menu_cursor()</CODE> will restore it to the 1410correct location for continuing menu driver processing. <P> 1411 1412It is possible to set hooks to be called at menu initialization and 1413wrapup time, and whenever the selected item changes. See 1414<CODE>menu_hook(3x)</CODE>. <P> 1415 1416Each item, and each menu, has an associated user pointer on which you 1417can hang application data. See <CODE>mitem_userptr(3x)</CODE> and 1418<CODE>menu_userptr(3x)</CODE>. 1419 1420<H1><A NAME="form">The Forms Library</A></H1> 1421 1422The <CODE>form</CODE> library is a curses extension that supports easy 1423programming of on-screen forms for data entry and program control. <P> 1424 1425The <CODE>form</CODE> library first appeared in AT&T System V. The 1426version documented here is the <CODE>form</CODE> code distributed 1427with <CODE>ncurses</CODE>. 1428 1429<H2><A NAME="fcompile">Compiling With the form Library</A></H2> 1430 1431Your form-using modules must import the form library declarations with 1432 1433<PRE> 1434 #include <form.h> 1435</PRE> 1436 1437and must be linked explicitly with the forms library using an 1438<CODE>-lform</CODE> argument. Note that they must also link the 1439<CODE>ncurses</CODE> library with <CODE>-lncurses</CODE>. Many linkers 1440are two-pass and will accept either order, but it is still good practice 1441to put <CODE>-lform</CODE> first and <CODE>-lncurses</CODE> second. 1442 1443<H2><A NAME="foverview">Overview of Forms</A></H2> 1444 1445A form is a collection of fields; each field may be either a label 1446(explanatory text) or a data-entry location. Long forms may be 1447segmented into pages; each entry to a new page clears the screen. <P> 1448To make forms, you create groups of fields and connect them with form 1449frame objects; the form library makes this relatively simple. <P> 1450 1451Once defined, a form can be <DFN>posted</DFN>, that is written to an 1452associated window. Actually, each form has two associated windows; a 1453containing window in which the programmer can scribble titles or 1454borders, and a subwindow in which the form fields proper are displayed. <P> 1455 1456As the form user fills out the posted form, navigation and editing 1457keys support movement between fields, editing keys support modifying 1458field, and plain text adds to or changes data in a current field. The 1459form library allows you (the forms designer) to bind each navigation 1460and editing key to any keystroke accepted by <CODE>curses</CODE> 1461 1462Fields may have validation conditions on them, so that they check input 1463data for type and value. The form library supplies a rich set of 1464pre-defined field types, and makes it relatively easy to define new ones. <P> 1465 1466Once its transaction is completed (or aborted), a form may be 1467<DFN>unposted</DFN> (that is, undisplayed), and finally freed to make 1468the storage associated with it and its items available for re-use. <P> 1469 1470The general flow of control of a form program looks like this: 1471 1472<OL> 1473<LI>Initialize <CODE>curses</CODE>. 1474<LI>Create the form fields, using <CODE>new_field()</CODE>. 1475<LI>Create the form using <CODE>new_form()</CODE>. 1476<LI>Post the form using <CODE>post_form()</CODE>. 1477<LI>Refresh the screen. 1478<LI>Process user requests via an input loop. 1479<LI>Unpost the form using <CODE>unpost_form()</CODE>. 1480<LI>Free the form, using <CODE>free_form()</CODE>. 1481<LI>Free the fields using <CODE>free_field()</CODE>. 1482<LI>Terminate <CODE>curses</CODE>. 1483</OL> 1484 1485Note that this looks much like a menu program; the form library handles 1486tasks which are in many ways similar, and its interface was obviously 1487designed to resemble that of the <A HREF="#menu">menu library</A> 1488wherever possible. <P> 1489 1490In forms programs, however, the `process user requests' is somewhat more 1491complicated than for menus. Besides menu-like navigation operations, 1492the menu driver loop has to support field editing and data validation. 1493 1494<H2><A NAME="fcreate">Creating and Freeing Fields and Forms</A></H2> 1495 1496The basic function for creating fields is <CODE>new_field()</CODE>: 1497 1498<PRE> 1499FIELD *new_field(int height, int width, /* new field size */ 1500 int top, int left, /* upper left corner */ 1501 int offscreen, /* number of offscreen rows */ 1502 int nbuf); /* number of working buffers */ 1503</PRE> 1504 1505Menu items always occupy a single row, but forms fields may have 1506multiple rows. So <CODE>new_field()</CODE> requires you to specify a 1507width and height (the first two arguments, which mist both be greater 1508than zero). <P> 1509 1510You must also specify the location of the field's upper left corner on 1511the screen (the third and fourth arguments, which must be zero or 1512greater). Note that these coordinates are relative to the form 1513subwindow, which will coincide with <CODE>stdscr</CODE> by default but 1514need not be <CODE>stdscr</CODE> if you've done an explicit 1515<CODE>set_form_win()</CODE> call. <P> 1516 1517The fifth argument allows you to specify a number of off-screen rows. If 1518this is zero, the entire field will always be displayed. If it is 1519nonzero, the form will be scrollable, with only one screen-full (initially 1520the top part) displayed at any given time. If you make a field dynamic 1521and grow it so it will no longer fit on the screen, the form will become 1522scrollable even if the <CODE>offscreen</CODE> argument was initially zero. <P> 1523 1524The forms library allocates one working buffer per field; the size of 1525each buffer is <CODE>((height + offscreen)*width + 1</CODE>, one character 1526for each position in the field plus a NUL terminator. The sixth 1527argument is the number of additional data buffers to allocate for the 1528field; your application can use them for its own purposes. 1529 1530<PRE> 1531FIELD *dup_field(FIELD *field, /* field to copy */ 1532 int top, int left); /* location of new copy */ 1533</PRE> 1534 1535The function <CODE>dup_field()</CODE> duplicates an existing field at a 1536new location. Size and buffering information are copied; some 1537attribute flags and status bits are not (see the 1538<CODE>form_field_new(3X)</CODE> for details). 1539 1540<PRE> 1541FIELD *link_field(FIELD *field, /* field to copy */ 1542 int top, int left); /* location of new copy */ 1543</PRE> 1544 1545The function <CODE>link_field()</CODE> also duplicates an existing field 1546at a new location. The difference from <CODE>dup_field()</CODE> is that 1547it arranges for the new field's buffer to be shared with the old one. <P> 1548 1549Besides the obvious use in making a field editable from two different 1550form pages, linked fields give you a way to hack in dynamic labels. If 1551you declare several fields linked to an original, and then make them 1552inactive, changes from the original will still be propagated to the 1553linked fields. <P> 1554 1555As with duplicated fields, linked fields have attribute bits separate 1556from the original. <P> 1557 1558As you might guess, all these field-allocations return <CODE>NULL</CODE> if 1559the field allocation is not possible due to an out-of-memory error or 1560out-of-bounds arguments. <P> 1561 1562To connect fields to a form, use 1563 1564<PRE> 1565FORM *new_form(FIELD **fields); 1566</PRE> 1567 1568This function expects to see a NULL-terminated array of field pointers. 1569Said fields are connected to a newly-allocated form object; its address 1570is returned (or else NULL if the allocation fails). <P> 1571 1572Note that <CODE>new_field()</CODE> does <EM>not</EM> copy the pointer array 1573into private storage; if you modify the contents of the pointer array 1574during forms processing, all manner of bizarre things might happen. Also 1575note that any given field may only be connected to one form. <P> 1576 1577The functions <CODE>free_field()</CODE> and <CODE>free_form</CODE> are available 1578to free field and form objects. It is an error to attempt to free a field 1579connected to a form, but not vice-versa; thus, you will generally free 1580your form objects first. 1581 1582<H2><A NAME="fattributes">Fetching and Changing Field Attributes</A></H2> 1583 1584Each form field has a number of location and size attributes 1585associated with it. There are other field attributes used to control 1586display and editing of the field. Some (for example, the <CODE>O_STATIC</CODE> bit) 1587involve sufficient complications to be covered in sections of their own 1588later on. We cover the functions used to get and set several basic 1589attributes here. <P> 1590 1591When a field is created, the attributes not specified by the 1592<CODE>new_field</CODE> function are copied from an invisible system 1593default field. In attribute-setting and -fetching functions, the 1594argument NULL is taken to mean this field. Changes to it persist 1595as defaults until your forms application terminates. 1596 1597<H3><A NAME="fsizes">Fetching Size and Location Data</A></H3> 1598 1599You can retrieve field sizes and locations through: 1600 1601<PRE> 1602int field_info(FIELD *field, /* field from which to fetch */ 1603 int *height, *int width, /* field size */ 1604 int *top, int *left, /* upper left corner */ 1605 int *offscreen, /* number of offscreen rows */ 1606 int *nbuf); /* number of working buffers */ 1607</PRE> 1608 1609This function is a sort of inverse of <CODE>new_field()</CODE>; instead of 1610setting size and location attributes of a new field, it fetches them 1611from an existing one. 1612 1613<H3><A NAME="flocation">Changing the Field Location</A></H3> 1614 1615It is possible to move a field's location on the screen: 1616 1617<PRE> 1618int move_field(FIELD *field, /* field to alter */ 1619 int top, int left); /* new upper-left corner */ 1620</PRE> 1621 1622You can, of course. query the current location through <CODE>field_info()</CODE>. 1623 1624<H3><A NAME="fjust">The Justification Attribute</A></H3> 1625 1626One-line fields may be unjustified, justified right, justified left, 1627or centered. Here is how you manipulate this attribute: 1628 1629<PRE> 1630int set_field_just(FIELD *field, /* field to alter */ 1631 int justmode); /* mode to set */ 1632 1633int field_just(FIELD *field); /* fetch mode of field */ 1634</PRE> 1635 1636The mode values accepted and returned by this functions are 1637preprocessor macros <CODE>NO_JUSTIFICATION</CODE>, <CODE>JUSTIFY_RIGHT</CODE>, 1638<CODE>JUSTIFY_LEFT</CODE>, or <CODE>JUSTIFY_CENTER</CODE>. 1639 1640<H3><A NAME="fdispatts">Field Display Attributes</A></H3> 1641 1642For each field, you can set a foreground attribute for entered 1643characters, a background attribute for the entire field, and a pad 1644character for the unfilled portion of the field. You can also 1645control pagination of the form. <P> 1646 1647This group of four field attributes controls the visual appearance 1648of the field on the screen, without affecting in any way the data 1649in the field buffer. 1650 1651<PRE> 1652int set_field_fore(FIELD *field, /* field to alter */ 1653 chtype attr); /* attribute to set */ 1654 1655chtype field_fore(FIELD *field); /* field to query */ 1656 1657int set_field_back(FIELD *field, /* field to alter */ 1658 chtype attr); /* attribute to set */ 1659 1660chtype field_back(FIELD *field); /* field to query */ 1661 1662int set_field_pad(FIELD *field, /* field to alter */ 1663 int pad); /* pad character to set */ 1664 1665chtype field_pad(FIELD *field); 1666 1667int set_new_page(FIELD *field, /* field to alter */ 1668 int flag); /* TRUE to force new page */ 1669 1670chtype new_page(FIELD *field); /* field to query */ 1671</PRE> 1672 1673The attributes set and returned by the first four functions are normal 1674<CODE>curses(3x)</CODE> display attribute values (<CODE>A_STANDOUT</CODE>, 1675<CODE>A_BOLD</CODE>, <CODE>A_REVERSE</CODE> etc). 1676 1677The page bit of a field controls whether it is displayed at the start of 1678a new form screen. 1679 1680<H3><A NAME="foptions">Field Option Bits</A></H3> 1681 1682There is also a large collection of field option bits you can set to control 1683various aspects of forms processing. You can manipulate them with these 1684functions: 1685 1686<PRE> 1687int set_field_opts(FIELD *field, /* field to alter */ 1688 int attr); /* attribute to set */ 1689 1690int field_opts_on(FIELD *field, /* field to alter */ 1691 int attr); /* attributes to turn on */ 1692 1693int field_opts_off(FIELD *field, /* field to alter */ 1694 int attr); /* attributes to turn off */ 1695 1696int field_opts(FIELD *field); /* field to query */ 1697</PRE> 1698 1699By default, all options are on. Here are the available option bits: 1700<DL> 1701<DT> O_VISIBLE 1702<DD> Controls whether the field is visible on the screen. Can be used 1703during form processing to hide or pop up fields depending on the value 1704of parent fields. 1705<DT> O_ACTIVE 1706<DD> Controls whether the field is active during forms processing (i.e. 1707visited by form navigation keys). Can be used to make labels or derived 1708fields with buffer values alterable by the forms application, not the user. 1709<DT> O_PUBLIC 1710<DD> Controls whether data is displayed during field entry. If this option is 1711turned off on a field, the library will accept and edit data in that field, 1712but it will not be displayed and the visible field cursor will not move. 1713You can turn off the O_PUBLIC bit to define password fields. 1714<DT> O_EDIT 1715<DD> Controls whether the field's data can be modified. When this option is 1716off, all editing requests except <CODE>REQ_PREV_CHOICE</CODE> and 1717<CODE>REQ_NEXT_CHOICE</CODE> will fail. Such read-only fields may be useful for 1718help messages. 1719<DT> O_WRAP 1720<DD> Controls word-wrapping in multi-line fields. Normally, when any 1721character of a (blank-separated) word reaches the end of the current line, the 1722entire word is wrapped to the next line (assuming there is one). When this 1723option is off, the word will be split across the line break. 1724<DT> O_BLANK 1725<DD> Controls field blanking. When this option is on, entering a character at 1726the first field position erases the entire field (except for the just-entered 1727character). 1728<DT> O_AUTOSKIP 1729<DD> Controls automatic skip to next field when this one fills. Normally, 1730when the forms user tries to type more data into a field than will fit, 1731the editing location jumps to next field. When this option is off, the 1732user's cursor will hang at the end of the field. This option is ignored 1733in dynamic fields that have not reached their size limit. 1734<DT> O_NULLOK 1735<DD> Controls whether <A HREF="#fvalidation">validation</A> is applied to 1736blank fields. Normally, it is not; the user can leave a field blank 1737without invoking the usual validation check on exit. If this option is 1738off on a field, exit from it will invoke a validation check. 1739<DT> O_PASSOK 1740<DD> Controls whether validation occurs on every exit, or only after 1741the field is modified. Normally the latter is true. Setting O_PASSOK 1742may be useful if your field's validation function may change during 1743forms processing. 1744<DT> O_STATIC 1745<DD> Controls whether the field is fixed to its initial dimensions. If you 1746turn this off, the field becomes <A HREF="#fdynamic">dynamic</A> and will 1747stretch to fit entered data. 1748</DL> 1749 1750A field's options cannot be changed while the field is currently selected. 1751However, options may be changed on posted fields that are not current. <P> 1752 1753The option values are bit-masks and can be composed with logical-or in 1754the obvious way. 1755 1756<H2><A NAME="fstatus">Field Status</A></H2> 1757 1758Every field has a status flag, which is set to FALSE when the field is 1759created and TRUE when the value in field buffer 0 changes. This flag can 1760be queried and set directly: 1761 1762<PRE> 1763int set_field_status(FIELD *field, /* field to alter */ 1764 int status); /* mode to set */ 1765 1766int field_status(FIELD *field); /* fetch mode of field */ 1767</PRE> 1768 1769Setting this flag under program control can be useful if you use the same 1770form repeatedly, looking for modified fields each time. <P> 1771 1772Calling <CODE>field_status()</CODE> on a field not currently selected 1773for input will return a correct value. Calling <CODE>field_status()</CODE> on a 1774field that is currently selected for input may not necessarily give a 1775correct field status value, because entered data isn't necessarily copied to 1776buffer zero before the exit validation check. 1777 1778To guarantee that the returned status value reflects reality, call 1779<CODE>field_status()</CODE> either (1) in the field's exit validation check 1780routine, (2) from the field's or form's initialization or termination 1781hooks, or (3) just after a <CODE>REQ_VALIDATION</CODE> request has been 1782processed by the forms driver. 1783 1784<H2><A NAME="fuser">Field User Pointer</A></H2> 1785 1786Each field structure contains one character pointer slot that is not used 1787by the forms library. It is intended to be used by applications to store 1788private per-field data. You can manipulate it with: 1789 1790<PRE> 1791int set_field_userptr(FIELD *field, /* field to alter */ 1792 char *userptr); /* mode to set */ 1793 1794char *field_userptr(FIELD *field); /* fetch mode of field */ 1795</PRE> 1796 1797(Properly, this user pointer field ought to have <CODE>(void *)</CODE> type. 1798The <CODE>(char *)</CODE> type is retained for System V compatibility.) <P> 1799 1800It is valid to set the user pointer of the default field (with a 1801<CODE>set_field_userptr()</CODE> call passed a NULL field pointer.) 1802When a new field is created, the default-field user pointer is copied 1803to initialize the new field's user pointer. 1804 1805<H2><A NAME="fdynamic">Variable-Sized Fields</A></H2> 1806 1807Normally, a field is fixed at the size specified for it at creation 1808time. If, however, you turn off its O_STATIC bit, it becomes 1809<DFN>dynamic</DFN> and will automatically resize itself to accommodate 1810data as it is entered. If the field has extra buffers associated with it, 1811they will grow right along with the main input buffer. <P> 1812 1813A one-line dynamic field will have a fixed height (1) but variable 1814width, scrolling horizontally to display data within the field area as 1815originally dimensioned and located. A multi-line dynamic field will 1816have a fixed width, but variable height (number of rows), scrolling 1817vertically to display data within the field area as originally 1818dimensioned and located. <P> 1819 1820Normally, a dynamic field is allowed to grow without limit. But it is 1821possible to set an upper limit on the size of a dynamic field. You do 1822it with this function: 1823 1824<PRE> 1825int set_max_field(FIELD *field, /* field to alter (may not be NULL) */ 1826 int max_size); /* upper limit on field size */ 1827</PRE> 1828 1829If the field is one-line, <CODE>max_size</CODE> is taken to be a column size 1830limit; if it is multi-line, it is taken to be a line size limit. To disable 1831any limit, use an argument of zero. The growth limit can be changed whether 1832or not the O_STATIC bit is on, but has no effect until it is. <P> 1833 1834The following properties of a field change when it becomes dynamic: 1835 1836<UL> 1837<LI>If there is no growth limit, there is no final position of the field; 1838therefore <CODE>O_AUTOSKIP</CODE> and <CODE>O_NL_OVERLOAD</CODE> are ignored. 1839<LI>Field justification will be ignored (though whatever justification is 1840set up will be retained internally and can be queried). 1841<LI>The <CODE>dup_field()</CODE> and <CODE>link_field()</CODE> calls copy 1842dynamic-buffer sizes. If the <CODE>O_STATIC</CODE> option is set on one of a 1843collection of links, buffer resizing will occur only when the field is 1844edited through that link. 1845<LI>The call <CODE>field_info()</CODE> will retrieve the original static size of 1846the field; use <CODE>dynamic_field_info()</CODE> to get the actual dynamic size. 1847</UL> 1848 1849<H2><A NAME="fvalidation">Field Validation</A></H2> 1850 1851By default, a field will accept any data that will fit in its input buffer. 1852However, it is possible to attach a validation type to a field. If you do 1853this, any attempt to leave the field while it contains data that doesn't 1854match the validation type will fail. Some validation types also have a 1855character-validity check for each time a character is entered in the field. <P> 1856 1857A field's validation check (if any) is not called when 1858<CODE>set_field_buffer()</CODE> modifies the input buffer, nor when that buffer 1859is changed through a linked field. <P> 1860 1861The <CODE>form</CODE> library provides a rich set of pre-defined validation 1862types, and gives you the capability to define custom ones of your own. You 1863can examine and change field validation attributes with the following 1864functions: 1865 1866<PRE> 1867int set_field_type(FIELD *field, /* field to alter */ 1868 FIELDTYPE *ftype, /* type to associate */ 1869 ...); /* additional arguments*/ 1870 1871FIELDTYPE *field_type(FIELD *field); /* field to query */ 1872</PRE> 1873 1874The validation type of a field is considered an attribute of the field. As 1875with other field attributes, Also, doing <CODE>set_field_type()</CODE> with a 1876<CODE>NULL</CODE> field default will change the system default for validation of 1877newly-created fields. <P> 1878 1879Here are the pre-defined validation types: 1880 1881<H3><A NAME="ftype_alpha">TYPE_ALPHA</A></H3> 1882 1883This field type accepts alphabetic data; no blanks, no digits, no special 1884characters (this is checked at character-entry time). It is set up with: 1885 1886<PRE> 1887int set_field_type(FIELD *field, /* field to alter */ 1888 TYPE_ALPHA, /* type to associate */ 1889 int width); /* maximum width of field */ 1890</PRE> 1891 1892The <CODE>width</CODE> argument sets a minimum width of data. Typically 1893you'll want to set this to the field width; if it's greater than the 1894field width, the validation check will always fail. A minimum width 1895of zero makes field completion optional. 1896 1897<H3><A NAME="ftype_alnum">TYPE_ALNUM</A></H3> 1898 1899This field type accepts alphabetic data and digits; no blanks, no special 1900characters (this is checked at character-entry time). It is set up with: 1901 1902<PRE> 1903int set_field_type(FIELD *field, /* field to alter */ 1904 TYPE_ALNUM, /* type to associate */ 1905 int width); /* maximum width of field */ 1906</PRE> 1907 1908The <CODE>width</CODE> argument sets a minimum width of data. As with 1909TYPE_ALPHA, typically you'll want to set this to the field width; if it's 1910greater than the field width, the validation check will always fail. A 1911minimum width of zero makes field completion optional. 1912 1913<H3><A NAME="ftype_enum">TYPE_ENUM</A></H3> 1914 1915This type allows you to restrict a field's values to be among a specified 1916set of string values (for example, the two-letter postal codes for U.S. 1917states). It is set up with: 1918 1919<PRE> 1920int set_field_type(FIELD *field, /* field to alter */ 1921 TYPE_ENUM, /* type to associate */ 1922 char **valuelist; /* list of possible values */ 1923 int checkcase; /* case-sensitive? */ 1924 int checkunique); /* must specify uniquely? */ 1925</PRE> 1926 1927The <CODE>valuelist</CODE> parameter must point at a NULL-terminated list of 1928valid strings. The <CODE>checkcase</CODE> argument, if true, makes comparison 1929with the string case-sensitive. <P> 1930 1931When the user exits a TYPE_ENUM field, the validation procedure tries to 1932complete the data in the buffer to a valid entry. If a complete choice string 1933has been entered, it is of course valid. But it is also possible to enter a 1934prefix of a valid string and have it completed for you. <P> 1935 1936By default, if you enter such a prefix and it matches more than one value 1937in the string list, the prefix will be completed to the first matching 1938value. But the <CODE>checkunique</CODE> argument, if true, requires prefix 1939matches to be unique in order to be valid. <P> 1940 1941The <CODE>REQ_NEXT_CHOICE</CODE> and <CODE>REQ_PREV_CHOICE</CODE> input requests 1942can be particularly useful with these fields. 1943 1944<H3><A NAME="ftype_integer">TYPE_INTEGER</A></H3> 1945 1946This field type accepts an integer. It is set up as follows: 1947 1948<PRE> 1949int set_field_type(FIELD *field, /* field to alter */ 1950 TYPE_INTEGER, /* type to associate */ 1951 int padding, /* # places to zero-pad to */ 1952 int vmin, int vmax); /* valid range */ 1953</PRE> 1954 1955Valid characters consist of an optional leading minus and digits. 1956The range check is performed on exit. If the range maximum is less 1957than or equal to the minimum, the range is ignored. <P> 1958 1959If the value passes its range check, it is padded with as many leading 1960zero digits as necessary to meet the padding argument. <P> 1961 1962A <CODE>TYPE_INTEGER</CODE> value buffer can conveniently be interpreted 1963with the C library function <CODE>atoi(3)</CODE>. 1964 1965<H3><A NAME="ftype_numeric">TYPE_NUMERIC</A></H3> 1966 1967This field type accepts a decimal number. It is set up as follows: 1968 1969<PRE> 1970int set_field_type(FIELD *field, /* field to alter */ 1971 TYPE_NUMERIC, /* type to associate */ 1972 int padding, /* # places of precision */ 1973 double vmin, double vmax); /* valid range */ 1974</PRE> 1975 1976Valid characters consist of an optional leading minus and digits. possibly 1977including a decimal point. If your system supports locale's, the decimal point 1978character used must be the one defined by your locale. The range check is 1979performed on exit. If the range maximum is less than or equal to the minimum, 1980the range is ignored. <P> 1981 1982If the value passes its range check, it is padded with as many trailing 1983zero digits as necessary to meet the padding argument. <P> 1984 1985A <CODE>TYPE_NUMERIC</CODE> value buffer can conveniently be interpreted 1986with the C library function <CODE>atof(3)</CODE>. 1987 1988<H3><A NAME="ftype_regexp">TYPE_REGEXP</A></H3> 1989 1990This field type accepts data matching a regular expression. It is set up 1991as follows: 1992 1993<PRE> 1994int set_field_type(FIELD *field, /* field to alter */ 1995 TYPE_REGEXP, /* type to associate */ 1996 char *regexp); /* expression to match */ 1997</PRE> 1998 1999The syntax for regular expressions is that of <CODE>regcomp(3)</CODE>. 2000The check for regular-expression match is performed on exit. 2001 2002<H2><A NAME="fbuffer">Direct Field Buffer Manipulation</A></H2> 2003 2004The chief attribute of a field is its buffer contents. When a form has 2005been completed, your application usually needs to know the state of each 2006field buffer. You can find this out with: 2007 2008<PRE> 2009char *field_buffer(FIELD *field, /* field to query */ 2010 int bufindex); /* number of buffer to query */ 2011</PRE> 2012 2013Normally, the state of the zero-numbered buffer for each field is set by 2014the user's editing actions on that field. It's sometimes useful to be able 2015to set the value of the zero-numbered (or some other) buffer from your 2016application: 2017 2018<PRE> 2019int set_field_buffer(FIELD *field, /* field to alter */ 2020 int bufindex, /* number of buffer to alter */ 2021 char *value); /* string value to set */ 2022</PRE> 2023 2024If the field is not large enough and cannot be resized to a sufficiently 2025large size to contain the specified value, the value will be truncated 2026to fit. <P> 2027 2028Calling <CODE>field_buffer()</CODE> with a null field pointer will raise an 2029error. Calling <CODE>field_buffer()</CODE> on a field not currently selected 2030for input will return a correct value. Calling <CODE>field_buffer()</CODE> on a 2031field that is currently selected for input may not necessarily give a 2032correct field buffer value, because entered data isn't necessarily copied to 2033buffer zero before the exit validation check. 2034 2035To guarantee that the returned buffer value reflects on-screen reality, 2036call <CODE>field_buffer()</CODE> either (1) in the field's exit validation 2037check routine, (2) from the field's or form's initialization or termination 2038hooks, or (3) just after a <CODE>REQ_VALIDATION</CODE> request has been processed 2039by the forms driver. 2040 2041<H2><A NAME="formattrs">Attributes of Forms</A></H2> 2042 2043As with field attributes, form attributes inherit a default from a 2044system default form structure. These defaults can be queried or set by 2045of these functions using a form-pointer argument of <CODE>NULL</CODE>. <P> 2046 2047The principal attribute of a form is its field list. You can query 2048and change this list with: 2049 2050<PRE> 2051int set_form_fields(FORM *form, /* form to alter */ 2052 FIELD **fields); /* fields to connect */ 2053 2054char *form_fields(FORM *form); /* fetch fields of form */ 2055 2056int field_count(FORM *form); /* count connect fields */ 2057</PRE> 2058 2059The second argument of <CODE>set_form_fields()</CODE> may be a 2060NULL-terminated field pointer array like the one required by 2061<CODE>new_form()</CODE>. In that case, the old fields of the form are 2062disconnected but not freed (and eligible to be connected to other 2063forms), then the new fields are connected. <P> 2064 2065It may also be null, in which case the old fields are disconnected 2066(and not freed) but no new ones are connected. <P> 2067 2068The <CODE>field_count()</CODE> function simply counts the number of fields 2069connected to a given from. It returns -1 if the form-pointer argument 2070is NULL. 2071 2072<H2><A NAME="fdisplay">Control of Form Display</A></H2> 2073 2074In the overview section, you saw that to display a form you normally 2075start by defining its size (and fields), posting it, and refreshing 2076the screen. There is an hidden step before posting, which is the 2077association of the form with a frame window (actually, a pair of 2078windows) within which it will be displayed. By default, the forms 2079library associates every form with the full-screen window 2080<CODE>stdscr</CODE>. <P> 2081 2082By making this step explicit, you can associate a form with a declared 2083frame window on your screen display. This can be useful if you want to 2084adapt the form display to different screen sizes, dynamically tile 2085forms on the screen, or use a form as part of an interface layout 2086managed by <A HREF="#panels">panels</A>. <P> 2087 2088The two windows associated with each form have the same functions as 2089their analogues in the <A HREF="#menu">menu library</A>. Both these 2090windows are painted when the form is posted and erased when the form 2091is unposted. <P> 2092 2093The outer or frame window is not otherwise touched by the form 2094routines. It exists so the programmer can associate a title, a 2095border, or perhaps help text with the form and have it properly 2096refreshed or erased at post/unpost time. The inner window or subwindow 2097is where the current form page is actually displayed. <P> 2098 2099In order to declare your own frame window for a form, you'll need to 2100know the size of the form's bounding rectangle. You can get this 2101information with: 2102 2103<PRE> 2104int scale_form(FORM *form, /* form to query */ 2105 int *rows, /* form rows */ 2106 int *cols); /* form cols */ 2107</PRE> 2108 2109The form dimensions are passed back in the locations pointed to by 2110the arguments. Once you have this information, you can use it to 2111declare of windows, then use one of these functions: 2112 2113<PRE> 2114int set_form_win(FORM *form, /* form to alter */ 2115 WINDOW *win); /* frame window to connect */ 2116 2117WINDOW *form_win(FORM *form); /* fetch frame window of form */ 2118 2119int set_form_sub(FORM *form, /* form to alter */ 2120 WINDOW *win); /* form subwindow to connect */ 2121 2122WINDOW *form_sub(FORM *form); /* fetch form subwindow of form */ 2123</PRE> 2124 2125Note that curses operations, including <CODE>refresh()</CODE>, on the form, 2126should be done on the frame window, not the form subwindow. <P> 2127 2128It is possible to check from your application whether all of a 2129scrollable field is actually displayed within the menu subwindow. Use 2130these functions: 2131 2132<PRE> 2133int data_ahead(FORM *form); /* form to be queried */ 2134 2135int data_behind(FORM *form); /* form to be queried */ 2136</PRE> 2137 2138The function <CODE>data_ahead()</CODE> returns TRUE if (a) the current 2139field is one-line and has undisplayed data off to the right, (b) the current 2140field is multi-line and there is data off-screen below it. <P> 2141 2142The function <CODE>data_behind()</CODE> returns TRUE if the first (upper 2143left hand) character position is off-screen (not being displayed). <P> 2144 2145Finally, there is a function to restore the form window's cursor to the 2146value expected by the forms driver: 2147 2148<PRE> 2149int pos_form_cursor(FORM *) /* form to be queried */ 2150</PRE> 2151 2152If your application changes the form window cursor, call this function before 2153handing control back to the forms driver in order to re-synchronize it. 2154 2155<H2><A NAME="fdriver">Input Processing in the Forms Driver</A></H2> 2156 2157The function <CODE>form_driver()</CODE> handles virtualized input requests 2158for form navigation, editing, and validation requests, just as 2159<CODE>menu_driver</CODE> does for menus (see the section on <A 2160HREF="#minput">menu input handling</A>). 2161 2162<PRE> 2163int form_driver(FORM *form, /* form to pass input to */ 2164 int request); /* form request code */ 2165</PRE> 2166 2167Your input virtualization function needs to take input and then convert it 2168to either an alphanumeric character (which is treated as data to be 2169entered in the currently-selected field), or a forms processing request. <P> 2170 2171The forms driver provides hooks (through input-validation and 2172field-termination functions) with which your application code can check 2173that the input taken by the driver matched what was expected. 2174 2175<H3><A NAME="fpage">Page Navigation Requests</A></H3> 2176 2177These requests cause page-level moves through the form, 2178triggering display of a new form screen. 2179 2180<DL> 2181<DT> <CODE>REQ_NEXT_PAGE</CODE> 2182<DD> Move to the next form page. 2183<DT> <CODE>REQ_PREV_PAGE</CODE> 2184<DD> Move to the previous form page. 2185<DT> <CODE>REQ_FIRST_PAGE</CODE> 2186<DD> Move to the first form page. 2187<DT> <CODE>REQ_LAST_PAGE</CODE> 2188<DD> Move to the last form page. 2189</DL> 2190 2191These requests treat the list as cyclic; that is, <CODE>REQ_NEXT_PAGE</CODE> 2192from the last page goes to the first, and <CODE>REQ_PREV_PAGE</CODE> from 2193the first page goes to the last. 2194 2195<H3><A NAME="ffield">Inter-Field Navigation Requests</A></H3> 2196 2197These requests handle navigation between fields on the same page. 2198 2199<DL> 2200<DT> <CODE>REQ_NEXT_FIELD</CODE> 2201<DD> Move to next field. 2202<DT> <CODE>REQ_PREV_FIELD</CODE> 2203<DD> Move to previous field. 2204<DT> <CODE>REQ_FIRST_FIELD</CODE> 2205<DD> Move to the first field. 2206<DT> <CODE>REQ_LAST_FIELD</CODE> 2207<DD> Move to the last field. 2208<DT> <CODE>REQ_SNEXT_FIELD</CODE> 2209<DD> Move to sorted next field. 2210<DT> <CODE>REQ_SPREV_FIELD</CODE> 2211<DD> Move to sorted previous field. 2212<DT> <CODE>REQ_SFIRST_FIELD</CODE> 2213<DD> Move to the sorted first field. 2214<DT> <CODE>REQ_SLAST_FIELD</CODE> 2215<DD> Move to the sorted last field. 2216<DT> <CODE>REQ_LEFT_FIELD</CODE> 2217<DD> Move left to field. 2218<DT> <CODE>REQ_RIGHT_FIELD</CODE> 2219<DD> Move right to field. 2220<DT> <CODE>REQ_UP_FIELD</CODE> 2221<DD> Move up to field. 2222<DT> <CODE>REQ_DOWN_FIELD</CODE> 2223<DD> Move down to field. 2224</DL> 2225 2226These requests treat the list of fields on a page as cyclic; that is, 2227<CODE>REQ_NEXT_FIELD</CODE> from the last field goes to the first, and 2228<CODE>REQ_PREV_FIELD</CODE> from the first field goes to the last. The 2229order of the fields for these (and the <CODE>REQ_FIRST_FIELD</CODE> and 2230<CODE>REQ_LAST_FIELD</CODE> requests) is simply the order of the field 2231pointers in the form array (as set up by <CODE>new_form()</CODE> or 2232<CODE>set_form_fields()</CODE> <P> 2233 2234It is also possible to traverse the fields as if they had been sorted in 2235screen-position order, so the sequence goes left-to-right and top-to-bottom. 2236To do this, use the second group of four sorted-movement requests. <P> 2237 2238Finally, it is possible to move between fields using visual directions up, 2239down, right, and left. To accomplish this, use the third group of four 2240requests. Note, however, that the position of a form for purposes of these 2241requests is its upper-left corner. <P> 2242 2243For example, suppose you have a multi-line field B, and two 2244single-line fields A and C on the same line with B, with A to the left 2245of B and C to the right of B. A <CODE>REQ_MOVE_RIGHT</CODE> from A will 2246go to B only if A, B, and C <EM>all</EM> share the same first line; 2247otherwise it will skip over B to C. 2248 2249<H3><A NAME="fifield">Intra-Field Navigation Requests</A></H3> 2250 2251These requests drive movement of the edit cursor within the currently 2252selected field. 2253 2254<DL> 2255<DT> <CODE>REQ_NEXT_CHAR</CODE> 2256<DD> Move to next character. 2257<DT> <CODE>REQ_PREV_CHAR</CODE> 2258<DD> Move to previous character. 2259<DT> <CODE>REQ_NEXT_LINE</CODE> 2260<DD> Move to next line. 2261<DT> <CODE>REQ_PREV_LINE</CODE> 2262<DD> Move to previous line. 2263<DT> <CODE>REQ_NEXT_WORD</CODE> 2264<DD> Move to next word. 2265<DT> <CODE>REQ_PREV_WORD</CODE> 2266<DD> Move to previous word. 2267<DT> <CODE>REQ_BEG_FIELD</CODE> 2268<DD> Move to beginning of field. 2269<DT> <CODE>REQ_END_FIELD</CODE> 2270<DD> Move to end of field. 2271<DT> <CODE>REQ_BEG_LINE</CODE> 2272<DD> Move to beginning of line. 2273<DT> <CODE>REQ_END_LINE</CODE> 2274<DD> Move to end of line. 2275<DT> <CODE>REQ_LEFT_CHAR</CODE> 2276<DD> Move left in field. 2277<DT> <CODE>REQ_RIGHT_CHAR</CODE> 2278<DD> Move right in field. 2279<DT> <CODE>REQ_UP_CHAR</CODE> 2280<DD> Move up in field. 2281<DT> <CODE>REQ_DOWN_CHAR</CODE> 2282<DD> Move down in field. 2283</DL> 2284 2285Each <EM>word</EM> is separated from the previous and next characters 2286by whitespace. The commands to move to beginning and end of line or field 2287look for the first or last non-pad character in their ranges. 2288 2289<H3><A NAME="fscroll">Scrolling Requests</A></H3> 2290 2291Fields that are dynamic and have grown and fields explicitly created 2292with offscreen rows are scrollable. One-line fields scroll horizontally; 2293multi-line fields scroll vertically. Most scrolling is triggered by 2294editing and intra-field movement (the library scrolls the field to keep the 2295cursor visible). It is possible to explicitly request scrolling with the 2296following requests: 2297 2298<DL> 2299<DT> <CODE>REQ_SCR_FLINE</CODE> 2300<DD> Scroll vertically forward a line. 2301<DT> <CODE>REQ_SCR_BLINE</CODE> 2302<DD> Scroll vertically backward a line. 2303<DT> <CODE>REQ_SCR_FPAGE</CODE> 2304<DD> Scroll vertically forward a page. 2305<DT> <CODE>REQ_SCR_BPAGE</CODE> 2306<DD> Scroll vertically backward a page. 2307<DT> <CODE>REQ_SCR_FHPAGE</CODE> 2308<DD> Scroll vertically forward half a page. 2309<DT> <CODE>REQ_SCR_BHPAGE</CODE> 2310<DD> Scroll vertically backward half a page. 2311<DT> <CODE>REQ_SCR_FCHAR</CODE> 2312<DD> Scroll horizontally forward a character. 2313<DT> <CODE>REQ_SCR_BCHAR</CODE> 2314<DD> Scroll horizontally backward a character. 2315<DT> <CODE>REQ_SCR_HFLINE</CODE> 2316<DD> Scroll horizontally one field width forward. 2317<DT> <CODE>REQ_SCR_HBLINE</CODE> 2318<DD> Scroll horizontally one field width backward. 2319<DT> <CODE>REQ_SCR_HFHALF</CODE> 2320<DD> Scroll horizontally one half field width forward. 2321<DT> <CODE>REQ_SCR_HBHALF</CODE> 2322<DD> Scroll horizontally one half field width backward. 2323</DL> 2324 2325For scrolling purposes, a <EM>page</EM> of a field is the height 2326of its visible part. 2327 2328<H3><A NAME="fedit">Editing Requests</A></H3> 2329 2330When you pass the forms driver an ASCII character, it is treated as a 2331request to add the character to the field's data buffer. Whether this 2332is an insertion or a replacement depends on the field's edit mode 2333(insertion is the default. <P> 2334 2335The following requests support editing the field and changing the edit 2336mode: 2337 2338<DL> 2339<DT> <CODE>REQ_INS_MODE</CODE> 2340<DD> Set insertion mode. 2341<DT> <CODE>REQ_OVL_MODE</CODE> 2342<DD> Set overlay mode. 2343<DT> <CODE>REQ_NEW_LINE</CODE> 2344<DD> New line request (see below for explanation). 2345<DT> <CODE>REQ_INS_CHAR</CODE> 2346<DD> Insert space at character location. 2347<DT> <CODE>REQ_INS_LINE</CODE> 2348<DD> Insert blank line at character location. 2349<DT> <CODE>REQ_DEL_CHAR</CODE> 2350<DD> Delete character at cursor. 2351<DT> <CODE>REQ_DEL_PREV</CODE> 2352<DD> Delete previous word at cursor. 2353<DT> <CODE>REQ_DEL_LINE</CODE> 2354<DD> Delete line at cursor. 2355<DT> <CODE>REQ_DEL_WORD</CODE> 2356<DD> Delete word at cursor. 2357<DT> <CODE>REQ_CLR_EOL</CODE> 2358<DD> Clear to end of line. 2359<DT> <CODE>REQ_CLR_EOF</CODE> 2360<DD> Clear to end of field. 2361<DT> <CODE>REQ_CLEAR_FIELD</CODE> 2362<DD> Clear entire field. 2363</DL> 2364 2365The behavior of the <CODE>REQ_NEW_LINE</CODE> and <CODE>REQ_DEL_PREV</CODE> requests 2366is complicated and partly controlled by a pair of forms options. 2367The special cases are triggered when the cursor is at the beginning of 2368a field, or on the last line of the field. <P> 2369 2370First, we consider <CODE>REQ_NEW_LINE</CODE>: <P> 2371 2372The normal behavior of <CODE>REQ_NEW_LINE</CODE> in insert mode is to break the 2373current line at the position of the edit cursor, inserting the portion of 2374the current line after the cursor as a new line following the current 2375and moving the cursor to the beginning of that new line (you may think 2376of this as inserting a newline in the field buffer). <P> 2377 2378The normal behavior of <CODE>REQ_NEW_LINE</CODE> in overlay mode is to clear the 2379current line from the position of the edit cursor to end of line. 2380The cursor is then moved to the beginning of the next line. <P> 2381 2382However, <CODE>REQ_NEW_LINE</CODE> at the beginning of a field, or on the 2383last line of a field, instead does a <CODE>REQ_NEXT_FIELD</CODE>. 2384<CODE>O_NL_OVERLOAD</CODE> option is off, this special action is 2385disabled. <P> 2386 2387Now, let us consider <CODE>REQ_DEL_PREV</CODE>: <P> 2388 2389The normal behavior of <CODE>REQ_DEL_PREV</CODE> is to delete the previous 2390character. If insert mode is on, and the cursor is at the start of a 2391line, and the text on that line will fit on the previous one, it 2392instead appends the contents of the current line to the previous one 2393and deletes the current line (you may think of this as deleting a 2394newline from the field buffer). <P> 2395 2396However, <CODE>REQ_DEL_PREV</CODE> at the beginning of a field is instead 2397treated as a <CODE>REQ_PREV_FIELD</CODE>. <P> If the 2398<CODE>O_BS_OVERLOAD</CODE> option is off, this special action is 2399disabled and the forms driver just returns <CODE>E_REQUEST_DENIED</CODE>. <P> 2400 2401See <A HREF="#frmoptions">Form Options</A> for discussion of how to set 2402and clear the overload options. 2403 2404<H3><A NAME="forder">Order Requests</A></H3> 2405 2406If the type of your field is ordered, and has associated functions 2407for getting the next and previous values of the type from a given value, 2408there are requests that can fetch that value into the field buffer: 2409 2410<DL> 2411<DT> <CODE>REQ_NEXT_CHOICE</CODE> 2412<DD> Place the successor value of the current value in the buffer. 2413<DT> <CODE>REQ_PREV_CHOICE</CODE> 2414<DD> Place the predecessor value of the current value in the buffer. 2415</DL> 2416 2417Of the built-in field types, only <CODE>TYPE_ENUM</CODE> has built-in successor 2418and predecessor functions. When you define a field type of your own 2419(see <A HREF="#fcustom">Custom Validation Types</A>), you can associate 2420our own ordering functions. 2421 2422<H3><A NAME="fappcmds">Application Commands</A></H3> 2423 2424Form requests are represented as integers above the <CODE>curses</CODE> value 2425greater than <CODE>KEY_MAX</CODE> and less than or equal to the constant 2426<CODE>MAX_COMMAND</CODE>. If your input-virtualization routine returns a 2427value above <CODE>MAX_COMMAND</CODE>, the forms driver will ignore it. 2428 2429<H2><A NAME="fhooks">Field Change Hooks</A></H2> 2430 2431It is possible to set function hooks to be executed whenever the 2432current field or form changes. Here are the functions that support this: 2433 2434<PRE> 2435typedef void (*HOOK)(); /* pointer to function returning void */ 2436 2437int set_form_init(FORM *form, /* form to alter */ 2438 HOOK hook); /* initialization hook */ 2439 2440HOOK form_init(FORM *form); /* form to query */ 2441 2442int set_form_term(FORM *form, /* form to alter */ 2443 HOOK hook); /* termination hook */ 2444 2445HOOK form_term(FORM *form); /* form to query */ 2446 2447int set_field_init(FORM *form, /* form to alter */ 2448 HOOK hook); /* initialization hook */ 2449 2450HOOK field_init(FORM *form); /* form to query */ 2451 2452int set_field_term(FORM *form, /* form to alter */ 2453 HOOK hook); /* termination hook */ 2454 2455HOOK field_term(FORM *form); /* form to query */ 2456</PRE> 2457 2458These functions allow you to either set or query four different hooks. 2459In each of the set functions, the second argument should be the 2460address of a hook function. These functions differ only in the timing 2461of the hook call. 2462 2463<DL> 2464<DT> form_init 2465<DD> This hook is called when the form is posted; also, just after 2466each page change operation. 2467<DT> field_init 2468<DD> This hook is called when the form is posted; also, just after 2469each field change 2470<DT> field_term 2471<DD> This hook is called just after field validation; that is, just before 2472the field is altered. It is also called when the form is unposted. 2473<DT> form_term 2474<DD> This hook is called when the form is unposted; also, just before 2475each page change operation. 2476</DL> 2477 2478Calls to these hooks may be triggered 2479<OL> 2480<LI>When user editing requests are processed by the forms driver 2481<LI>When the current page is changed by <CODE>set_current_field()</CODE> call 2482<LI>When the current field is changed by a <CODE>set_form_page()</CODE> call 2483</OL> 2484 2485See <A NAME="ffocus">Field Change Commands</A> for discussion of the latter 2486two cases. <P> 2487 2488You can set a default hook for all fields by passing one of the set functions 2489a NULL first argument. <P> 2490 2491You can disable any of these hooks by (re)setting them to NULL, the default 2492value. 2493 2494<H2><A HREF="#ffocus">Field Change Commands</A></H2> 2495 2496Normally, navigation through the form will be driven by the user's 2497input requests. But sometimes it is useful to be able to move the 2498focus for editing and viewing under control of your application, or 2499ask which field it currently is in. The following functions help you 2500accomplish this: 2501 2502<PRE> 2503int set_current_field(FORM *form, /* form to alter */ 2504 FIELD *field); /* field to shift to */ 2505 2506FIELD *current_field(FORM *form); /* form to query */ 2507 2508int field_index(FORM *form, /* form to query */ 2509 FIELD *field); /* field to get index of */ 2510</PRE> 2511 2512The function <CODE>field_index()</CODE> returns the index of the given field 2513in the given form's field array (the array passed to <CODE>new_form()</CODE> or 2514<CODE>set_form_fields()</CODE>). <P> 2515 2516The initial current field of a form is the first active field on the 2517first page. The function <CODE>set_form_fields()</CODE> resets this.<P> 2518 2519It is also possible to move around by pages. 2520 2521<PRE> 2522int set_form_page(FORM *form, /* form to alter */ 2523 int page); /* page to go to (0-origin) */ 2524 2525int form_page(FORM *form); /* return form's current page */ 2526</PRE> 2527 2528The initial page of a newly-created form is 0. The function 2529<CODE>set_form_fields()</CODE> resets this. 2530 2531<H2><A NAME="frmoptions">Form Options</A></H2> 2532 2533Like fields, forms may have control option bits. They can be changed 2534or queried with these functions: 2535 2536<PRE> 2537int set_form_opts(FORM *form, /* form to alter */ 2538 int attr); /* attribute to set */ 2539 2540int form_opts_on(FORM *form, /* form to alter */ 2541 int attr); /* attributes to turn on */ 2542 2543int form_opts_off(FORM *form, /* form to alter */ 2544 int attr); /* attributes to turn off */ 2545 2546int form_opts(FORM *form); /* form to query */ 2547</PRE> 2548 2549By default, all options are on. Here are the available option bits: 2550 2551<DL> 2552<DT> O_NL_OVERLOAD 2553<DD> Enable overloading of <CODE>REQ_NEW_LINE</CODE> as described in <A 2554href="#fedit">Editing Requests</A>. The value of this option is 2555ignored on dynamic fields that have not reached their size limit; 2556these have no last line, so the circumstances for triggering a 2557<CODE>REQ_NEXT_FIELD</CODE> never arise. 2558<DT> O_BS_OVERLOAD 2559<DD> Enable overloading of <CODE>REQ_DEL_PREV</CODE> as described in 2560<A href="#fedit">Editing Requests</A>. 2561</DL> 2562 2563The option values are bit-masks and can be composed with logical-or in 2564the obvious way. 2565 2566<H2><A NAME="fcustom">Custom Validation Types</A></H2> 2567 2568The <CODE>form</CODE> library gives you the capability to define custom 2569validation types of your own. Further, the optional additional arguments 2570of <CODE>set_field_type</CODE> effectively allow you to parameterize validation 2571types. Most of the complications in the validation-type interface have to 2572do with the handling of the additional arguments within custom validation 2573functions. 2574 2575<H3><A NAME="flinktypes">Union Types</A></H3> 2576 2577The simplest way to create a custom data type is to compose it from two 2578preexisting ones: 2579 2580<PRE> 2581FIELD *link_fieldtype(FIELDTYPE *type1, 2582 FIELDTYPE *type2); 2583</PRE> 2584 2585This function creates a field type that will accept any of the values 2586legal for either of its argument field types (which may be either 2587predefined or programmer-defined). 2588 2589If a <CODE>set_field_type()</CODE> call later requires arguments, the new 2590composite type expects all arguments for the first type, than all arguments 2591for the second. Order functions (see <A HREF="#forder">Order Requests</A>) 2592associated with the component types will work on the composite; what it does 2593is check the validation function for the first type, then for the second, to 2594figure what type the buffer contents should be treated as. 2595 2596<H3><A NAME="fnewtypes">New Field Types</A></H3> 2597 2598To create a field type from scratch, you need to specify one or both of the 2599following things: 2600 2601<UL> 2602<LI>A character-validation function, to check each character as it is entered. 2603<LI>A field-validation function to be applied on exit from the field. 2604</UL> 2605 2606Here's how you do that: 2607<PRE> 2608typedef int (*HOOK)(); /* pointer to function returning int */ 2609 2610FIELDTYPE *new_fieldtype(HOOK f_validate, /* field validator */ 2611 HOOK c_validate) /* character validator */ 2612 2613 2614int free_fieldtype(FIELDTYPE *ftype); /* type to free */ 2615</PRE> 2616 2617At least one of the arguments of <CODE>new_fieldtype()</CODE> must be 2618non-NULL. The forms driver will automatically call the new type's 2619validation functions at appropriate points in processing a field of 2620the new type. <P> 2621 2622The function <CODE>free_fieldtype()</CODE> deallocates the argument 2623fieldtype, freeing all storage associated with it. <P> 2624 2625Normally, a field validator is called when the user attempts to 2626leave the field. Its first argument is a field pointer, from which it 2627can get to field buffer 0 and test it. If the function returns TRUE, 2628the operation succeeds; if it returns FALSE, the edit cursor stays in 2629the field. <P> 2630 2631A character validator gets the character passed in as a first argument. 2632It too should return TRUE if the character is valid, FALSE otherwise. 2633 2634<H3><A NAME="fcheckargs">Validation Function Arguments</A></H3> 2635 2636Your field- and character- validation functions will be passed a 2637second argument as well. This second argument is the address of a 2638structure (which we'll call a <EM>pile</EM>) built from any of the 2639field-type-specific arguments passed to <CODE>set_field_type()</CODE>. If 2640no such arguments are defined for the field type, this pile pointer 2641argument will be NULL. <P> 2642 2643In order to arrange for such arguments to be passed to your validation 2644functions, you must associate a small set of storage-management functions 2645with the type. The forms driver will use these to synthesize a pile 2646from the trailing arguments of each <CODE>set_field_type()</CODE> argument, and 2647a pointer to the pile will be passed to the validation functions. <P> 2648 2649Here is how you make the association: 2650 2651<PRE> 2652typedef char *(*PTRHOOK)(); /* pointer to function returning (char *) */ 2653typedef void (*VOIDHOOK)(); /* pointer to function returning void */ 2654 2655int set_fieldtype_arg(FIELDTYPE *type, /* type to alter */ 2656 PTRHOOK make_str, /* make structure from args */ 2657 PTRHOOK copy_str, /* make copy of structure */ 2658 VOIDHOOK free_str); /* free structure storage */ 2659</PRE> 2660 2661Here is how the storage-management hooks are used: 2662 2663<DL> 2664<DT> <CODE>make_str</CODE> 2665<DD> This function is called by <CODE>set_field_type()</CODE>. It gets one 2666argument, a <CODE>va_list</CODE> of the type-specific arguments passed to 2667<CODE>set_field_type()</CODE>. It is expected to return a pile pointer to a data 2668structure that encapsulates those arguments. 2669<DT> <CODE>copy_str</CODE> 2670<DD> This function is called by form library functions that allocate new 2671field instances. It is expected to take a pile pointer, copy the pile 2672to allocated storage, and return the address of the pile copy. 2673<DT> <CODE>free_str</CODE> 2674<DD> This function is called by field- and type-deallocation routines in the 2675library. It takes a pile pointer argument, and is expected to free the 2676storage of that pile. 2677</DL> 2678 2679The <CODE>make_str</CODE> and <CODE>copy_str</CODE> functions may return NULL to 2680signal allocation failure. The library routines will that call them will 2681return error indication when this happens. Thus, your validation functions 2682should never see a NULL file pointer and need not check specially for it. 2683 2684<H3><A NAME="fcustorder">Order Functions For Custom Types</A></H3> 2685 2686Some custom field types are simply ordered in the same well-defined way 2687that <CODE>TYPE_ENUM</CODE> is. For such types, it is possible to define 2688successor and predecessor functions to support the <CODE>REQ_NEXT_CHOICE</CODE> 2689and <CODE>REQ_PREV_CHOICE</CODE> requests. Here's how: 2690 2691<PRE> 2692typedef int (*INTHOOK)(); /* pointer to function returning int */ 2693 2694int set_fieldtype_arg(FIELDTYPE *type, /* type to alter */ 2695 INTHOOK succ, /* get successor value */ 2696 INTHOOK pred); /* get predecessor value */ 2697</PRE> 2698 2699The successor and predecessor arguments will each be passed two arguments; 2700a field pointer, and a pile pointer (as for the validation functions). They 2701are expected to use the function <CODE>field_buffer()</CODE> to read the 2702current value, and <CODE>set_field_buffer()</CODE> on buffer 0 to set the next 2703or previous value. Either hook may return TRUE to indicate success (a 2704legal next or previous value was set) or FALSE to indicate failure. 2705 2706<H3><A NAME="fcustprobs">Avoiding Problems</A></H3> 2707 2708The interface for defining custom types is complicated and tricky. 2709Rather than attempting to create a custom type entirely from scratch, 2710you should start by studying the library source code for whichever of 2711the pre-defined types seems to be closest to what you want. <P> 2712 2713Use that code as a model, and evolve it towards what you really want. 2714You will avoid many problems and annoyances that way. The code 2715in the <CODE>ncurses</CODE> library has been specifically exempted from 2716the package copyright to support this. <P> 2717 2718If your custom type defines order functions, have do something intuitive 2719with a blank field. A useful convention is to make the successor of a 2720blank field the types minimum value, and its predecessor the maximum. 2721</BODY> 2722</HTML> 2723