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| Viewing file: Select action/file-type: Writing Programs with NCURSESby Eric S. Raymond and Zeyd M. Ben-Halim Contents
IntroductionThis document is an introduction to programming with
This document is aimed at C applications programmers not yet
specifically familiar with ncurses. If you are already an
experienced The The A Brief History of CursesHistorically, the first ancestor of System III UNIX from Bell Labs featured a rewritten and
much-improved Scope of This DocumentThis document describes
Also, this package makes use of the insert and delete line and character features of terminals so equipped, and determines how to optimally use these features with no help from the programmer. It allows arbitrary combinations of video attributes to be displayed, even on terminals that leave “magic cookies” on the screen to mark changes in attributes. The The This document also describes the panels extension library, similarly modeled on the SVr4 panels facility. This library allows you to associate backing store with each of a stack or deck of overlapping windows, and provides operations for moving windows around in the stack that change their visibility in the natural way (handling window overlaps). Finally, this document describes in detail the menus and forms extension libraries, also cloned from System V, which support easy construction and sequences of menus and fill-in forms. TerminologyIn this document, the following terminology is used with reasonable consistency:
The Curses LibraryAn Overview of CursesCompiling Programs using CursesIn order to use the library, it is necessary to have certain types and variables defined. Therefore, the programmer must have a line:
#include <curses.h>
at the top of the program source. The screen package uses the
Standard I/O library, so Updating the ScreenIn order to update the screen optimally, it is necessary for
the routines to know what the screen currently looks like and
what the programmer wants it to look like next. For this purpose,
a data type (structure) named WINDOW is defined which describes a
window image to the routines, including its starting position on
the screen (the (y, x) coordinates of the upper left hand corner)
and its size. One of these (called A window is a purely internal representation. It is used to build and store a potential image of a portion of the terminal. It does not bear any necessary relation to what is really on the terminal screen; it is more like a scratchpad or write buffer. To make the section of physical screen corresponding to a
window reflect the contents of the window structure, the routine
A given physical screen section may be within the scope of any number of overlapping windows. Also, changes can be made to windows in any order, without regard to motion efficiency. Then, at will, the programmer can effectively say “make it look like this,” and let the package implementation determine the most efficient way to repaint the screen. Standard Windows and Function Naming ConventionsAs hinted above, the routines can use several windows, but two
are automatically given: Many functions are defined to use In order to move the current (y, x) coordinates from one point
to another, the routines
move(y, x);
addch(ch);
can be replaced by
mvaddch(y, x, ch);
and
wmove(win, y, x);
waddch(win, ch);
can be replaced by
mvwaddch(win, y, x, ch);
Note that the window description pointer (win) comes before the added (y, x) coordinates. If a function requires a window pointer, it is always the first parameter passed. VariablesThe
type name description
------------------------------------------------------------------
int LINES number of lines on the terminal
int COLS number of columns on the terminal
The
Using the LibraryNow we describe how to actually use the screen package. In it,
we assume all updating, reading, etc. is applied to
Here is a sample program to motivate the discussion:
#include <stdlib.h>
#include <curses.h>
#include <signal.h>
static void finish(int sig);
int
main(int argc, char *argv[])
{
int num = 0;
/* initialize your non-curses data structures here */
(void) signal(SIGINT, finish); /* arrange interrupts to terminate */
(void) initscr(); /* initialize the curses library */
keypad(stdscr, TRUE); /* enable keyboard mapping */
(void) nonl(); /* tell curses not to do NL->CR/NL on output */
(void) cbreak(); /* take input chars one at a time, no wait for \n */
(void) echo(); /* echo input - in color */
if (has_colors())
{
start_color();
/*
* Simple color assignment, often all we need. Color pair 0 cannot
* be redefined. This example uses the same value for the color
* pair as for the foreground color, though of course that is not
* necessary:
*/
init_pair(1, COLOR_RED, COLOR_BLACK);
init_pair(2, COLOR_GREEN, COLOR_BLACK);
init_pair(3, COLOR_YELLOW, COLOR_BLACK);
init_pair(4, COLOR_BLUE, COLOR_BLACK);
init_pair(5, COLOR_CYAN, COLOR_BLACK);
init_pair(6, COLOR_MAGENTA, COLOR_BLACK);
init_pair(7, COLOR_WHITE, COLOR_BLACK);
}
for (;;)
{
int c = getch(); /* refresh, accept single keystroke of input */
attrset(COLOR_PAIR(num % 8));
num++;
/* process the command keystroke */
}
finish(0); /* we are done */
}
static void finish(int sig)
{
endwin();
/* do your non-curses wrapup here */
exit(0);
}
Starting upIn order to use the screen package, the routines must know
about terminal characteristics, and the space for
Once the screen windows have been allocated, you can set them
up for your program. If you want to, say, allow a screen to
scroll, use You can create new windows of your own using the functions
OutputNow that we have set things up, we will want to actually
update the terminal. The basic functions used to change what will
go on a window are The other output functions, such as After you have put on the window what you want there, when you
want the portion of the terminal covered by the window to be made
to look like it, you must call If you call InputThe complementary function to When you need to accept line-oriented input in a window, the
functions The example code above uses the call Using Forms CharactersThe The most useful of the ACS defines are the forms-drawing
characters. You can use these to draw boxes and simple graphs on
the screen. If the terminal does not have such characters,
Character Attributes and ColorThe Highlights are encoded, internally, as high bits of the
pseudo-character type ( There are two ways to make highlights. One is to logical-or
the value of the highlights you want into the character argument
of an The other is to set the current-highlight value. This is
logical-ORed with any highlight you specify the first
way. You do this with the functions Once you have done an Mouse InterfacingThe
NOTE: this facility is specific to
Presently, mouse event reporting works in the following environments:
The mouse interface is very simple. To activate it, you use
the function Once the mouse is active, your application's command loop
should watch for a return value of Each call to The mouse structure contains two additional fields which may be significant in the future as ncurses interfaces to new kinds of pointing device. In addition to x and y coordinates, there is a slot for a z coordinate; this might be useful with touch-screens that can return a pressure or duration parameter. There is also a device ID field, which could be used to distinguish between multiple pointing devices. The class of visible events may be changed at any time via
A function to check whether a mouse event fell within a given window is also supplied. You can use this to see whether a given window should consider a mouse event relevant to it. Because mouse event reporting will not be available in all
environments, it would be unwise to build See the manual page Finishing UpIn order to clean up after the Function DescriptionsWe describe the detailed behavior of some important curses functions here, as a supplement to the manual page descriptions. Initialization and Wrapup
Causing Output to the Terminal
Low-Level Capability Access
DebuggingNOTE: These functions are not part of the standard curses API!
Trace logs can be difficult to interpret due to the sheer
volume of data dumped in them. There is a script called
tracemunch included with the
Hints, Tips, and TricksThe Some Notes of CautionIf you find yourself thinking you need to use
Bear in mind that You are much less likely to run into problems if you design
your screen layouts to use tiled rather than overlapping windows.
Historically, curses support for overlapping windows has been
weak, fragile, and poorly documented. The There is a panels library included in the Try to avoid using the global variables LINES and COLS. Use
Temporarily Leaving NCURSES ModeSometimes you will want to write a program that spends most of
its time in screen mode, but occasionally returns to ordinary
“cooked” mode. A common reason for this is to support
shell-out. This behavior is simple to arrange in
To leave There is a boolean function, Here is some sample code for shellout:
addstr("Shelling out...");
def_prog_mode(); /* save current tty modes */
endwin(); /* restore original tty modes */
system("sh"); /* run shell */
addstr("returned.\n"); /* prepare return message */
refresh(); /* restore save modes, repaint screen */
Using NCURSES under XTERMA resize operation in X sends That is the standard way, of course (it even works with some
vendor's curses implementations). Its drawback is that it clears
the screen to reinitialize the display, and does not resize
subwindows which must be shrunk. The Handling Multiple Terminal ScreensThe For each call, you will have to specify a terminal type and a
pair of file pointers; each call will return a screen reference,
and Testing for Terminal CapabilitiesSometimes you may want to write programs that test for the
presence of various capabilities before deciding whether to go
into A particularly useful case of this often comes up when you
want to test whether a given terminal type should be treated as
“smart” (cursor-addressable) or “stupid”.
The right way to test this is to see if the return value of
Tuning for SpeedUse the Special Features of NCURSESThe The The Ncurses supports up 16 colors, unlike SVr4 curses which defines only 8. While most terminals which provide color allow only 8 colors, about a quarter (including XFree86 xterm) support 16 colors. Compatibility with Older VersionsDespite our best efforts, there are some differences between
Refresh of Overlapping WindowsIf you define two windows A and B that overlap, and then
alternately scribble on and refresh them, the changes made to the
overlapping region under historic To understand why this is a problem, remember that screen updates are calculated between two representations of the entire display. The documentation says that when you refresh a window, it is first copied to the virtual screen, and then changes are calculated to update the physical screen (and applied to the terminal). But "copied to" is not very specific, and subtle differences in how copying works can produce different behaviors in the case where two overlapping windows are each being refreshed at unpredictable intervals. What happens to the overlapping region depends on what
The For most commercial curses implementations, it is not
documented and not known for sure (at least not to the
It might therefore be unwise to rely on either behavior in
programs that might have to be linked with other curses
implementations. Instead, you can do an explicit
The really clean way to handle this is to use the panels
library. If, when you want a screen update, you do
Background EraseIf you have been using a very old versions of
In newer versions, this is not so. Instead, the attribute of
erased blanks is normal unless and until it is modified by the
functions This change in behavior conforms XSI Curses ConformanceThe One effect of XSI conformance is the change in behavior described under "Background Erase -- Compatibility with Old Versions". Also, The Panels LibraryThe When your interface design is such that windows may dive deeper into the visibility stack or pop to the top at runtime, the resulting book-keeping can be tedious and difficult to get right. Hence the panels library. The Compiling With the Panels LibraryYour panels-using modules must import the panels library declarations with
#include <panel.h>
and must be linked explicitly with the panels library using an
Overview of PanelsA panel object is a window that is implicitly treated as part
of a deck including all other panel objects. The deck
has an implicit bottom-to-top visibility order. The panels
library includes an update function (analogous to
Details on the panels functions are available in the man pages. We will just hit the highlights here. You create a panel from a window by calling
You can delete a panel (removing it from the deck) with
To move a panel's window, use Two functions ( The function Typically, you will want to call Panels, Input, and the Standard ScreenYou should not mix The Note that There is presently no way to display changes to one obscured panel without repainting all panels. Hiding PanelsIt is possible to remove a panel from the deck temporarily;
use The Miscellaneous Other FacilitiesIt is possible to navigate the deck using the functions
Every panel has an associated user pointer, not used by the
panel code, to which you can attach application data. See the man
page documentation of The Menu LibraryA menu is a screen display that assists the user to choose
some subset of a given set of items. The The Compiling With the menu LibraryYour menu-using modules must import the menu library declarations with
#include <menu.h>
and must be linked explicitly with the menus library using an
Overview of MenusThe menus created by this library consist of collections of items including a name string part and a description string part. To make menus, you create groups of these items and connect them with menu frame objects. The menu can then by posted, that is written to an associated window. Actually, each menu has two associated windows; a containing window in which the programmer can scribble titles or borders, and a subwindow in which the menu items proper are displayed. If this subwindow is too small to display all the items, it will be a scrollable viewport on the collection of items. A menu may also be unposted (that is, undisplayed), and finally freed to make the storage associated with it and its items available for re-use. The general flow of control of a menu program looks like this:
Selecting itemsMenus may be multi-valued or (the default) single-valued (see
the manual page From a single-valued menu you can read the selected value
simply by looking at the current item. From a multi-valued menu,
you get the selected set by looping through the items applying
the Menu items can be made unselectable using
Menu DisplayThe menu library calculates a minimum display size for your window, based on the following variables:
The function The actual menu page may be smaller than the format size. This depends on the item number and size and whether O_ROWMAJOR is on. This option (on by default) causes menu items to be displayed in a “raster-scan” pattern, so that if more than one item will fit horizontally the first couple of items are side-by-side in the top row. The alternative is column-major display, which tries to put the first several items in the first column. As mentioned above, a menu format not large enough to allow all items to fit on-screen will result in a menu display that is vertically scrollable. You can scroll it with requests to the menu driver, which will be described in the section on menu input handling. Each menu has a mark string used to visually tag
selected items; see the The function Menu WindowsEach menu has, as mentioned previously, a pair of associated windows. Both these windows are painted when the menu is posted and erased when the menu is unposted. The outer or frame window is not otherwise touched by the menu routines. It exists so the programmer can associate a title, a border, or perhaps help text with the menu and have it properly refreshed or erased at post/unpost time. The inner window or subwindow is where the current menu page is displayed. By default, both windows are When you call Processing Menu InputThe main loop of your menu-processing code should call
The simplest group of command codes is
There are explicit requests for scrolling which also change
the current item (because the select location does not change,
but the item there does). These are The Each menu has an associated pattern buffer. The
Some requests change the pattern buffer directly:
Each successful scroll or item navigation request clears the
pattern buffer. It is also possible to set the pattern buffer
explicitly with Finally, menu driver requests above the constant
Miscellaneous Other FeaturesVarious menu options can affect the processing and visual
appearance and input processing of menus. See It is possible to change the current item from application
code; this is useful if you want to write your own navigation
requests. It is also possible to explicitly set the top row of
the menu display. See It is possible to set hooks to be called at menu
initialization and wrapup time, and whenever the selected item
changes. See Each item, and each menu, has an associated user pointer on
which you can hang application data. See
The Forms LibraryThe The Compiling With the form LibraryYour form-using modules must import the form library declarations with
#include <form.h>
and must be linked explicitly with the forms library using an
Overview of FormsA form is a collection of fields; each field may be either a label (explanatory text) or a data-entry location. Long forms may be segmented into pages; each entry to a new page clears the screen. To make forms, you create groups of fields and connect them with form frame objects; the form library makes this relatively simple. Once defined, a form can be posted, that is written to an associated window. Actually, each form has two associated windows; a containing window in which the programmer can scribble titles or borders, and a subwindow in which the form fields proper are displayed. As the form user fills out the posted form, navigation and
editing keys support movement between fields, editing keys
support modifying field, and plain text adds to or changes data
in a current field. The form library allows you (the forms
designer) to bind each navigation and editing key to any
keystroke accepted by Once its transaction is completed (or aborted), a form may be unposted (that is, undisplayed), and finally freed to make the storage associated with it and its items available for re-use. The general flow of control of a form program looks like this:
Note that this looks much like a menu program; the form library handles tasks which are in many ways similar, and its interface was obviously designed to resemble that of the menu library wherever possible. In forms programs, however, the “process user requests” is somewhat more complicated than for menus. Besides menu-like navigation operations, the menu driver loop has to support field editing and data validation. Creating and Freeing Fields and FormsThe basic function for creating fields is
FIELD *new_field(int height, int width, /* new field size */
int top, int left, /* upper left corner */
int offscreen, /* number of offscreen rows */
int nbuf); /* number of working buffers */
Menu items always occupy a single row, but forms fields may
have multiple rows. So You must also specify the location of the field's upper left
corner on the screen (the third and fourth arguments, which must
be zero or greater). Note that these coordinates are relative to
the form subwindow, which will coincide with The fifth argument allows you to specify a number of
off-screen rows. If this is zero, the entire field will always be
displayed. If it is nonzero, the form will be scrollable, with
only one screen-full (initially the top part) displayed at any
given time. If you make a field dynamic and grow it so it will no
longer fit on the screen, the form will become scrollable even if
the The forms library allocates one working buffer per field; the
size of each buffer is
FIELD *dup_field(FIELD *field, /* field to copy */
int top, int left); /* location of new copy */
The function
FIELD *link_field(FIELD *field, /* field to copy */
int top, int left); /* location of new copy */
The function Besides the obvious use in making a field editable from two different form pages, linked fields give you a way to hack in dynamic labels. If you declare several fields linked to an original, and then make them inactive, changes from the original will still be propagated to the linked fields. As with duplicated fields, linked fields have attribute bits separate from the original. As you might guess, all these field-allocations return
To connect fields to a form, use FORM *new_form(FIELD **fields); This function expects to see a NULL-terminated array of field pointers. Said fields are connected to a newly-allocated form object; its address is returned (or else NULL if the allocation fails). Note that The functions Fetching and Changing Field AttributesEach form field has a number of location and size attributes
associated with it. There are other field attributes used to
control display and editing of the field. Some (for example, the
When a field is created, the attributes not specified by the
Fetching Size and Location DataYou can retrieve field sizes and locations through:
int field_info(FIELD *field, /* field from which to fetch */
int *height, *int width, /* field size */
int *top, int *left, /* upper left corner */
int *offscreen, /* number of offscreen rows */
int *nbuf); /* number of working buffers */
This function is a sort of inverse of
Changing the Field LocationIt is possible to move a field's location on the screen:
int move_field(FIELD *field, /* field to alter */
int top, int left); /* new upper-left corner */
You can, of course. query the current location through
The Justification AttributeOne-line fields may be unjustified, justified right, justified left, or centered. Here is how you manipulate this attribute:
int set_field_just(FIELD *field, /* field to alter */
int justmode); /* mode to set */
int field_just(FIELD *field); /* fetch mode of field */
The mode values accepted and returned by this functions are
preprocessor macros Field Display AttributesFor each field, you can set a foreground attribute for entered characters, a background attribute for the entire field, and a pad character for the unfilled portion of the field. You can also control pagination of the form. This group of four field attributes controls the visual appearance of the field on the screen, without affecting in any way the data in the field buffer.
int set_field_fore(FIELD *field, /* field to alter */
chtype attr); /* attribute to set */
chtype field_fore(FIELD *field); /* field to query */
int set_field_back(FIELD *field, /* field to alter */
chtype attr); /* attribute to set */
chtype field_back(FIELD *field); /* field to query */
int set_field_pad(FIELD *field, /* field to alter */
int pad); /* pad character to set */
chtype field_pad(FIELD *field);
int set_new_page(FIELD *field, /* field to alter */
int flag); /* TRUE to force new page */
chtype new_page(FIELD *field); /* field to query */
The attributes set and returned by the first four functions
are normal Field Option BitsThere is also a large collection of field option bits you can set to control various aspects of forms processing. You can manipulate them with these functions:
int set_field_opts(FIELD *field, /* field to alter */
int attr); /* attribute to set */
int field_opts_on(FIELD *field, /* field to alter */
int attr); /* attributes to turn on */
int field_opts_off(FIELD *field, /* field to alter */
int attr); /* attributes to turn off */
int field_opts(FIELD *field); /* field to query */
By default, all options are on. Here are the available option bits:
A field's options cannot be changed while the field is currently selected. However, options may be changed on posted fields that are not current. The option values are bit-masks and can be composed with logical-or in the obvious way. Field StatusEvery field has a status flag, which is set to FALSE when the field is created and TRUE when the value in field buffer 0 changes. This flag can be queried and set directly:
int set_field_status(FIELD *field, /* field to alter */
int status); /* mode to set */
int field_status(FIELD *field); /* fetch mode of field */
Setting this flag under program control can be useful if you use the same form repeatedly, looking for modified fields each time. Calling Field User PointerEach field structure contains one character pointer slot that is not used by the forms library. It is intended to be used by applications to store private per-field data. You can manipulate it with:
int set_field_userptr(FIELD *field, /* field to alter */
char *userptr); /* mode to set */
char *field_userptr(FIELD *field); /* fetch mode of field */
(Properly, this user pointer field ought to have (void
*) type. The (char *) type is retained for
System V compatibility.)
It is valid to set the user pointer of the default field (with
a Variable-Sized FieldsNormally, a field is fixed at the size specified for it at creation time. If, however, you turn off its O_STATIC bit, it becomes dynamic and will automatically resize itself to accommodate data as it is entered. If the field has extra buffers associated with it, they will grow right along with the main input buffer. A one-line dynamic field will have a fixed height (1) but variable width, scrolling horizontally to display data within the field area as originally dimensioned and located. A multi-line dynamic field will have a fixed width, but variable height (number of rows), scrolling vertically to display data within the field area as originally dimensioned and located. Normally, a dynamic field is allowed to grow without limit. But it is possible to set an upper limit on the size of a dynamic field. You do it with this function:
int set_max_field(FIELD *field, /* field to alter (may not be NULL) */
int max_size); /* upper limit on field size */
If the field is one-line, The following properties of a field change when it becomes dynamic:
Field ValidationBy default, a field will accept any data that will fit in its input buffer. However, it is possible to attach a validation type to a field. If you do this, any attempt to leave the field while it contains data that does not match the validation type will fail. Some validation types also have a character-validity check for each time a character is entered in the field. A field's validation check (if any) is not called when
The
int set_field_type(FIELD *field, /* field to alter */
FIELDTYPE *ftype, /* type to associate */
...); /* additional arguments*/
FIELDTYPE *field_type(FIELD *field); /* field to query */
The validation type of a field is considered an attribute of
the field. As with other field attributes, Also, doing
Here are the pre-defined validation types: TYPE_ALPHAThis field type accepts alphabetic data; no blanks, no digits, no special characters (this is checked at character-entry time). It is set up with:
int set_field_type(FIELD *field, /* field to alter */
TYPE_ALPHA, /* type to associate */
int width); /* maximum width of field */
The TYPE_ALNUMThis field type accepts alphabetic data and digits; no blanks, no special characters (this is checked at character-entry time). It is set up with:
int set_field_type(FIELD *field, /* field to alter */
TYPE_ALNUM, /* type to associate */
int width); /* maximum width of field */
The TYPE_ENUMThis type allows you to restrict a field's values to be among a specified set of string values (for example, the two-letter postal codes for U.S. states). It is set up with:
int set_field_type(FIELD *field, /* field to alter */
TYPE_ENUM, /* type to associate */
char **valuelist; /* list of possible values */
int checkcase; /* case-sensitive? */
int checkunique); /* must specify uniquely? */
The When the user exits a TYPE_ENUM field, the validation procedure tries to complete the data in the buffer to a valid entry. If a complete choice string has been entered, it is of course valid. But it is also possible to enter a prefix of a valid string and have it completed for you. By default, if you enter such a prefix and it matches more
than one value in the string list, the prefix will be completed
to the first matching value. But the The TYPE_INTEGERThis field type accepts an integer. It is set up as follows:
int set_field_type(FIELD *field, /* field to alter */
TYPE_INTEGER, /* type to associate */
int padding, /* # places to zero-pad to */
int vmin, int vmax); /* valid range */
Valid characters consist of an optional leading minus and digits. The range check is performed on exit. If the range maximum is less than or equal to the minimum, the range is ignored. If the value passes its range check, it is padded with as many leading zero digits as necessary to meet the padding argument. A TYPE_NUMERICThis field type accepts a decimal number. It is set up as follows:
int set_field_type(FIELD *field, /* field to alter */
TYPE_NUMERIC, /* type to associate */
int padding, /* # places of precision */
double vmin, double vmax); /* valid range */
Valid characters consist of an optional leading minus and digits. possibly including a decimal point. If your system supports locale's, the decimal point character used must be the one defined by your locale. The range check is performed on exit. If the range maximum is less than or equal to the minimum, the range is ignored. If the value passes its range check, it is padded with as many trailing zero digits as necessary to meet the padding argument. A TYPE_REGEXPThis field type accepts data matching a regular expression. It is set up as follows:
int set_field_type(FIELD *field, /* field to alter */
TYPE_REGEXP, /* type to associate */
char *regexp); /* expression to match */
The syntax for regular expressions is that of
Direct Field Buffer ManipulationThe chief attribute of a field is its buffer contents. When a form has been completed, your application usually needs to know the state of each field buffer. You can find this out with:
char *field_buffer(FIELD *field, /* field to query */
int bufindex); /* number of buffer to query */
Normally, the state of the zero-numbered buffer for each field is set by the user's editing actions on that field. It is sometimes useful to be able to set the value of the zero-numbered (or some other) buffer from your application:
int set_field_buffer(FIELD *field, /* field to alter */
int bufindex, /* number of buffer to alter */
char *value); /* string value to set */
If the field is not large enough and cannot be resized to a sufficiently large size to contain the specified value, the value will be truncated to fit. Calling Attributes of FormsAs with field attributes, form attributes inherit a default
from a system default form structure. These defaults can be
queried or set by of these functions using a form-pointer
argument of The principal attribute of a form is its field list. You can query and change this list with:
int set_form_fields(FORM *form, /* form to alter */
FIELD **fields); /* fields to connect */
char *form_fields(FORM *form); /* fetch fields of form */
int field_count(FORM *form); /* count connect fields */
The second argument of It may also be null, in which case the old fields are disconnected (and not freed) but no new ones are connected. The Control of Form DisplayIn the overview section, you saw that to display a form you
normally start by defining its size (and fields), posting it, and
refreshing the screen. There is an hidden step before posting,
which is the association of the form with a frame window
(actually, a pair of windows) within which it will be displayed.
By default, the forms library associates every form with the
full-screen window By making this step explicit, you can associate a form with a declared frame window on your screen display. This can be useful if you want to adapt the form display to different screen sizes, dynamically tile forms on the screen, or use a form as part of an interface layout managed by panels. The two windows associated with each form have the same functions as their analogues in the menu library. Both these windows are painted when the form is posted and erased when the form is unposted. The outer or frame window is not otherwise touched by the form routines. It exists so the programmer can associate a title, a border, or perhaps help text with the form and have it properly refreshed or erased at post/unpost time. The inner window or subwindow is where the current form page is actually displayed. In order to declare your own frame window for a form, you will need to know the size of the form's bounding rectangle. You can get this information with:
int scale_form(FORM *form, /* form to query */
int *rows, /* form rows */
int *cols); /* form cols */
The form dimensions are passed back in the locations pointed to by the arguments. Once you have this information, you can use it to declare of windows, then use one of these functions:
int set_form_win(FORM *form, /* form to alter */
WINDOW *win); /* frame window to connect */
WINDOW *form_win(FORM *form); /* fetch frame window of form */
int set_form_sub(FORM *form, /* form to alter */
WINDOW *win); /* form subwindow to connect */
WINDOW *form_sub(FORM *form); /* fetch form subwindow of form */
Note that curses operations, including It is possible to check from your application whether all of a scrollable field is actually displayed within the menu subwindow. Use these functions: int data_ahead(FORM *form); /* form to be queried */ int data_behind(FORM *form); /* form to be queried */ The function The function Finally, there is a function to restore the form window's cursor to the value expected by the forms driver: int pos_form_cursor(FORM *) /* form to be queried */ If your application changes the form window cursor, call this function before handing control back to the forms driver in order to re-synchronize it. Input Processing in the Forms DriverThe function
int form_driver(FORM *form, /* form to pass input to */
int request); /* form request code */
Your input virtualization function needs to take input and then convert it to either an alphanumeric character (which is treated as data to be entered in the currently-selected field), or a forms processing request. The forms driver provides hooks (through input-validation and field-termination functions) with which your application code can check that the input taken by the driver matched what was expected. Page Navigation RequestsThese requests cause page-level moves through the form, triggering display of a new form screen.
These requests treat the list as cyclic; that is,
Inter-Field Navigation RequestsThese requests handle navigation between fields on the same page.
These requests treat the list of fields on a page as cyclic;
that is, It is also possible to traverse the fields as if they had been sorted in screen-position order, so the sequence goes left-to-right and top-to-bottom. To do this, use the second group of four sorted-movement requests. Finally, it is possible to move between fields using visual directions up, down, right, and left. To accomplish this, use the third group of four requests. Note, however, that the position of a form for purposes of these requests is its upper-left corner. For example, suppose you have a multi-line field B, and two
single-line fields A and C on the same line with B, with A to the
left of B and C to the right of B. A Intra-Field Navigation RequestsThese requests drive movement of the edit cursor within the currently selected field.
Each word is separated from the previous and next characters by whitespace. The commands to move to beginning and end of line or field look for the first or last non-pad character in their ranges. Scrolling RequestsFields that are dynamic and have grown and fields explicitly created with offscreen rows are scrollable. One-line fields scroll horizontally; multi-line fields scroll vertically. Most scrolling is triggered by editing and intra-field movement (the library scrolls the field to keep the cursor visible). It is possible to explicitly request scrolling with the following requests:
For scrolling purposes, a page of a field is the height of its visible part. Editing RequestsWhen you pass the forms driver an ASCII character, it is treated as a request to add the character to the field's data buffer. Whether this is an insertion or a replacement depends on the field's edit mode (insertion is the default. The following requests support editing the field and changing the edit mode:
The behavior of the First, we consider The normal behavior of The normal behavior of However, Now, let us consider The normal behavior of However, If the See Form Options for discussion of how to set and clear the overload options. Order RequestsIf the type of your field is ordered, and has associated functions for getting the next and previous values of the type from a given value, there are requests that can fetch that value into the field buffer:
Of the built-in field types, only Application CommandsForm requests are represented as integers above the
Field Change HooksIt is possible to set function hooks to be executed whenever the current field or form changes. Here are the functions that support this:
typedef void (*HOOK)(); /* pointer to function returning void */
int set_form_init(FORM *form, /* form to alter */
HOOK hook); /* initialization hook */
HOOK form_init(FORM *form); /* form to query */
int set_form_term(FORM *form, /* form to alter */
HOOK hook); /* termination hook */
HOOK form_term(FORM *form); /* form to query */
int set_field_init(FORM *form, /* form to alter */
HOOK hook); /* initialization hook */
HOOK field_init(FORM *form); /* form to query */
int set_field_term(FORM *form, /* form to alter */
HOOK hook); /* termination hook */
HOOK field_term(FORM *form); /* form to query */
These functions allow you to either set or query four different hooks. In each of the set functions, the second argument should be the address of a hook function. These functions differ only in the timing of the hook call.
Calls to these hooks may be triggered
See Field Change Commands for discussion of the latter two cases. You can set a default hook for all fields by passing one of the set functions a NULL first argument. You can disable any of these hooks by (re)setting them to NULL, the default value. Field Change CommandsNormally, navigation through the form will be driven by the user's input requests. But sometimes it is useful to be able to move the focus for editing and viewing under control of your application, or ask which field it currently is in. The following functions help you accomplish this:
int set_current_field(FORM *form, /* form to alter */
FIELD *field); /* field to shift to */
FIELD *current_field(FORM *form); /* form to query */
int field_index(FORM *form, /* form to query */
FIELD *field); /* field to get index of */
The function The initial current field of a form is the first active field
on the first page. The function It is also possible to move around by pages.
int set_form_page(FORM *form, /* form to alter */
int page); /* page to go to (0-origin) */
int form_page(FORM *form); /* return form's current page */
The initial page of a newly-created form is 0. The function
Form OptionsLike fields, forms may have control option bits. They can be changed or queried with these functions:
int set_form_opts(FORM *form, /* form to alter */
int attr); /* attribute to set */
int form_opts_on(FORM *form, /* form to alter */
int attr); /* attributes to turn on */
int form_opts_off(FORM *form, /* form to alter */
int attr); /* attributes to turn off */
int form_opts(FORM *form); /* form to query */
By default, all options are on. Here are the available option bits:
The option values are bit-masks and can be composed with logical-or in the obvious way. Custom Validation TypesThe Union TypesThe simplest way to create a custom data type is to compose it from two preexisting ones:
FIELD *link_fieldtype(FIELDTYPE *type1,
FIELDTYPE *type2);
This function creates a field type that will accept any of the
values legal for either of its argument field types (which may be
either predefined or programmer-defined). If a
New Field TypesTo create a field type from scratch, you need to specify one or both of the following things:
Here is how you do that:
typedef int (*HOOK)(); /* pointer to function returning int */
FIELDTYPE *new_fieldtype(HOOK f_validate, /* field validator */
HOOK c_validate) /* character validator */
int free_fieldtype(FIELDTYPE *ftype); /* type to free */
At least one of the arguments of The function Normally, a field validator is called when the user attempts to leave the field. Its first argument is a field pointer, from which it can get to field buffer 0 and test it. If the function returns TRUE, the operation succeeds; if it returns FALSE, the edit cursor stays in the field. A character validator gets the character passed in as a first argument. It too should return TRUE if the character is valid, FALSE otherwise. Validation Function ArgumentsYour field- and character- validation functions will be passed
a second argument as well. This second argument is the address of
a structure (which we will call a pile) built from any
of the field-type-specific arguments passed to
In order to arrange for such arguments to be passed to your
validation functions, you must associate a small set of
storage-management functions with the type. The forms driver will
use these to synthesize a pile from the trailing arguments of
each Here is how you make the association:
typedef char *(*PTRHOOK)(); /* pointer to function returning (char *) */
typedef void (*VOIDHOOK)(); /* pointer to function returning void */
int set_fieldtype_arg(FIELDTYPE *type, /* type to alter */
PTRHOOK make_str, /* make structure from args */
PTRHOOK copy_str, /* make copy of structure */
VOIDHOOK free_str); /* free structure storage */
Here is how the storage-management hooks are used:
The Order Functions For Custom TypesSome custom field types are simply ordered in the same
well-defined way that
typedef int (*INTHOOK)(); /* pointer to function returning int */
int set_fieldtype_arg(FIELDTYPE *type, /* type to alter */
INTHOOK succ, /* get successor value */
INTHOOK pred); /* get predecessor value */
The successor and predecessor arguments will each be passed
two arguments; a field pointer, and a pile pointer (as for the
validation functions). They are expected to use the function
Avoiding ProblemsThe interface for defining custom types is complicated and tricky. Rather than attempting to create a custom type entirely from scratch, you should start by studying the library source code for whichever of the pre-defined types seems to be closest to what you want. Use that code as a model, and evolve it towards what you
really want. You will avoid many problems and annoyances that
way. The code in the If your custom type defines order functions, have do something intuitive with a blank field. A useful convention is to make the successor of a blank field the types minimum value, and its predecessor the maximum. |
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