Intro --
Introduction to the X/Open Curses terminal operations interface
Synopsis
cc [options] file-lcurses
#include <curses.h>
Interface overview
This manual page and the rest of the
Section 3curses manual pages in Section 3curses manual pages
describe the Curses terminal interface library that is compiled by
default when you specify:
This version of the curses library, found in
/usr/lib/libcurses.a, complies with the
X/Open Curses, Issue 4 Version 2
standard found in
The Single UNIX® Specification, Version 2.
Note that the traditional curses library used by default in prior
releases of SCO UnixWare 1 and 2 is found in
/usr/lib/libocurses.a
and is documented on the
Section 3ocurses manual pages in Section 3ocurses manual pages.
Also note that the
panels(3ocurses),
menus(3ocurses),
and
forms(3ocurses),
libraries will work only with the SVR4
curses library, and will not
work properly if compiled with the X/Open version of curses.
Applications that compile with these libraries will need to change to
compile with the -locurses option of cc if
recompiled on UnixWare 7.0.1 or later versions.
Components
A Curses initialization function, usually
initscr(3curses),
determines the terminal model in use, by reference to either an argument or an
environment variable.
If that model is defined in terminfo, then the
same terminfo entry tells Curses
exactly how to operate the terminal.
In this case, a comprehensive API lets the application perform
terminal operations.
The Curses run-time system receives each terminal request and
sends appropriate commands to the terminal to achieve the desired effect.
Relationship to the general terminal interface
Applications using Curses should not also control the terminal using
capabilities of the general terminal interface, as described in
``Terminal device control'' in Programming with system calls and libraries
and in
termio(7).
Definitions
ancestors
The term ancestor refers to a window's parent, or its parent, and so on.
background
A property of a window that specifies a character (the background character)
and a rendition to be used in a variety of situations.
See
``Window Properties''.
Curses window
Data structures, which can be thought of as two-dimensional arrays of
characters that represent screen displays.
These data structures are manipulated with Curses functions.
cursor position
The line and column position on the screen denoted by the terminal's cursor.
derived windows
Derived windows are subwindows whose position is defined by reference to the
parent window rather than in absolute screen coordinates.
Derived windows are
otherwise no different from subwindows.
empty wide-character string
A wide-character string whose first element is a null wide-character code.
erase character
A special input character that deletes the last character in the current line,
if there is one.
kill character
A special input character that deletes all data in the current line, if there
are any.
null chtype
A chtype with all bits set to zero.
null wide-character code
A wide-character code with all bits set to zero.
pad
A pad is a specialised case of subwindow that is not necessarily associated
with a viewable part of a screen.
Functions that deal with pads are discussed in
``Synchronous and Networked Asynchronous Terminals''.
parent window
A window that has subwindows or derived windows associated with it.
rendition
The rendition of a character displayed on the screen is its attributes
and a colour pair.
SCREEN
A screen is the physical output device of the terminal. In Curses,
a SCREEN data type is an opaque data type associated with a terminal.
Each window is associated with a SCREEN.
subwindow
A window created within another window (called the
parent window), and positioned relative to the parent window.
Changes made to a subwindow do not affect its parent window.
Changes to a parent window will affect both subwindows and derived windows.
A subwindow can be created by calling
derwin(3curses),
newpad(3curses)
or
subwin(3curses).
Subwindows can be created from a parent window by calling
subwin(3curses).
The position and size of subwindows on the screen must be identical to or
totally within the parent window.
Window clipping is not a property of subwindows.
(A derived window differs from a subwindow only in that it is
positioned relative to the origin of its parent window.)
terminal
A terminal is the logical input and output device through which
character-based applications interact with the user.
TERMINAL is an opaque data type associated with a terminal.
A TERMINAL data structure primarily contains information
about the capabilities of the terminal, as defined by terminfo
(see
terminfo(4)).
A TERMINAL also contains information about the terminal modes
and current state for input and output operations.
Each screen is associated with a TERMINAL.
touch
To set a flag in a window that indicates that the information in the window
could differ from the that displayed on the terminal device.
wide-character code (C language)
An integer value corresponding to a single graphic symbol or control code.
wide-character string
A contiguous sequence of wide-character codes terminated by and
including the first null wide-character code.
window
The Curses functions permit manipulation of window
objects, which can be thought of as two-dimensional arrays of characters and
their renditions.
A default window called stdscr,
which is the size of the terminal screen, is supplied.
Others may be created with
newwin(3curses).
Variables declared as WINDOW * refer to windows (and to subwindows,
derived windows, and pads, as described below).
These data structures are manipulated with functions described on the
reference manual pages in
terminfo(4).
Among the most basic functions are
move(3curses)
and
addch(3curses).
More general versions of these functions are included that allow a process to
specify a window.
After using functions to manipulate a window,
refresh(3curses)
is called, telling Curses to make the CRT screen look like
stdscr.
Line drawing characters may be specified to be output. On input, Curses
is also able to translate arrow and function keys that transmit escape
sequences into single values. The line drawing characters
and input values use names defined in
curses.h.
Each window has a flag that indicates that the information in the window could
differ from the information displayed on the terminal device.
Making any change to the contents of the window, moving or modifying the
window, or setting the window's cursor position, sets this flag
(touches the window).
Refreshing the window clears this flag.
(For further information, see
``Synchronous and Networked Asynchronous Terminals''.
window hierarchy
The aggregate of a parent window and all of its subwindows and derived windows.
Characters
Character Storage Size
Historically, a position on the screen has corresponded to a single stored
byte.
This correspondence is no longer true for several reasons:
Attributes can be specified using constants with the A_
prefix specified in curses.h.
The A_ constants manipulate attributes in objects of type
chtype.
Additional attributes can be specified using constants with the
WA_ prefix.
The WA_ constants manipulate attributes in objects of type
attr_t.
Two constants that begin with A_ and WA_ and
that represent the same terminal capability refer to the same attribute
in the terminfo database and in the window data structure.
The effect on a window does not
differ depending on whether the application specifies A_
or WA_ constants.
For example, when an application updates window attributes
using the interfaces that support the A_ values, a query of the window
attribute using the function that returns WA_ values reflects this
update.
When it updates window attributes using the interfaces that
support the WA_ values, for which corresponding A_
values exist, a query
of the window attribute using the function that returns A_ values
reflects this update.
Rendition
The rendition of a character displayed on the screen is its attributes
and a color pair.
The rendition of a character written to the screen
becomes a property of the character and moves with
the character through any scrolling and insert/delete line/character
operations. To the extent possible on a particular terminal, a character's
rendition corresponds to the graphic rendition of the character
put on the screen.
If a given terminal does not support a rendition that an application
program is trying to use, Curses may substitute a different rendition for it.
Colors are always used in pairs (referred to as color-pairs).
A color-pair consists of a foreground color (for characters) and
a background color (for the field on which the characters are displayed).
Non-spacing Characters
The requirements in this section are in effect only for implementations
that claim Enhanced Curses compliance.
Some character sets may contain non-spacing characters.
(Non-spacing characters are those, other than the ' ' character,
for which
wcwidth(3C)
returns a width of zero.)
The application may write non-spacing characters to a window.
Every non-spacing character in a window is associated with a
spacing character and modifies the spacing character.
Non-spacing characters in a window cannot be addressed separately.
A non-spacing character is implicitly addressed whenever a Curses
operation affects the spacing character
with which the non-spacing character is associated.
Non-spacing characters do not support attributes.
For interfaces that use wide characters and
attributes, the attributes are ignored if the wide character is a non-spacing
character.
Multi-column characters have a single set of attributes for all columns.
The association of non-spacing characters with spacing characters can be
controlled by the application using the wide character interfaces.
The wide
character string functions provide codeset-dependent association.
Two typical effects of a non-spacing character associated with a spacing
character called c, are as follows:
The non-spacing character may modify the appearance
of c.
(For instance, there may be non-spacing characters that add
diacritical marks to characters.
However, there may also be spacing
characters with built-in diacritical marks.)
The non-spacing character may bridge c to the character following
c.
(Examples of this usage are the formation of ligatures and the
conversion of characters into compound display forms, words, or ideograms.)
Implementations may limit the number of non-spacing characters that can be
associated with a spacing character, provided any limit is at least ``5''.
Complex Characters
A complex character
is a set of associated characters, which may include a spacing character
and may include any non-spacing characters associated with it.
A spacing complex character is a spacing character followed by any
non-spacing characters associated with it.
That is, a spacing complex character is a complex character that includes
one spacing character.
An example of a code set that has complex characters
is ISO/IEC 10646-1:1993.
A complex character can be written to the screen; if it does not include a
spacing character, any non-spacing characters are associated with the
spacing complex character that exists at the specified screen position.
When
the application reads information back from the screen, it obtains spacing
complex characters.
The
cchar_t
data type represents a complex character and its rendition.
When a
cchar_t
represents a non-spacing complex character (that is, when there is no spacing
character within the complex character), then its rendition is not used; when
it is written to the screen, it uses the rendition specified by the spacing
character already displayed.
An object of type cchar_t can be initialized using
setcchar(3curses)
and its contents can be extracted using
getcchar(3curses).
The behavior of functions that take a cchar_t input argument is
undefined if the application provides a cchar_t value that was not
initialized in this way or obtained from a Curses
function that has a cchar_t output argument.
Each window has a rendition, which is combined with the rendition component of
the window's background property described below.
Window Background
Each window has a background property.
The background property specifies:
A spacing complex character (the background character) that will be used in a
variety of situations where visible information is deleted from the screen.
Many Curses functions use a coordinate pair.
In the Description sections of each Curses manual page,
coordinate locations are represented as (y, x)
since the y
argument always precedes the x argument in the function call.
These coordinates denote a line/column position, not a character position.
The coordinate y always refers to the row (of the window), and x
always refers to the column.
The first row and the first column is number 0, not 1.
The position ``(0, 0)'' is the window's origin.
For example, for terminals that display the ISO 8859-1 character set (with
left-to-right writing), ``(0, 0)'' represents the upper
left-hand corner of the screen.
Functions that start with mv
take arguments that specify a (y, x) position and
move the cursor (as though
move(3curses)
were called) before performing the requested action. As part of the requested
action, further cursor movement may occur, specified on the respective
reference manual page.
Basic Character Operations
Adding (Overwriting)
The Curses functions that contain the word add, such as
addch(3curses),
actually specify one or more characters to replace (overwrite) characters
already in the window.
If these functions specify only non-spacing
characters, they are appended to a spacing character already in the window;
see also
``Non-spacing Characters''.
When replacing a multi-column character with a character that requires fewer
columns, the new character is added starting at the specified or implied
column position. All columns that the former multi-column character
occupied that the new character does not require are orphaned columns,
which are filled using the background character and rendition.
Replacing a character with a character that requires more columns also
replaces one or more subsequent characters on the line.
This process may also produce orphaned columns.
Truncation, Wrapping and Scrolling
If the application specifies a character or a string of characters
such that writing them to a window would extend beyond the end of the line
(for example, if the application tries to deposit any multi-column character
at the last column in a line),
the behavior depends on whether the function supports line wrapping:
If the function does not wrap, it fails.
If the function wraps, then it places one or more characters in the window at
the start of the next line, beginning with the first character
that would not completely fit on the original line.
If the final character on the line is a multi-column character that does not
completely fit on the line, the entire character wraps to the next line and
columns at the end of the original line may be orphaned.
If the original line was the last line in the window, the wrap may cause a
scroll to occur:
If scrolling is enabled, a scroll occurs. The contents of the first line of
the window are lost. The contents of each remaining line in the window move
to the previous line. The last line of the window is filled with any
characters that wrapped. Any remaining space on the last line is
filled with the background character and rendition.
If scrolling is disabled, any characters that would extend beyond
the last column of the last line are truncated.
Some add functions move the cursor just beyond the end of the last
character added.
If this position is beyond the end of a line, it causes
wrapping and scrolling under the conditions specified in the second bullet
above.
Insertion
Insertion functions (such as
insch(3curses))
insert characters immediately before the character at the specified or implied
cursor position.
The insertion shifts all characters that were formerly at or beyond the
cursor position on the cursor line toward the end of that line. The
disposition of the characters that would thus extend beyond the end of the
line depends on whether the function supports wrapping:
If the function does not wrap, those characters are removed from the window.
This may produce orphaned columns.
If the function supports wrapping, the effect is as described in
``Truncation, Wrapping and Scrolling''
(except that the overwriting discussed in the final dash is an insertion).
If multi-column characters are displayed, some cursor positions are within a
multi-column character but not at the beginning of a character.
Any request
to insert data at a position that is not the beginning of a multi-column
character will be adjusted so that the actual cursor position is at the
beginning of the multi-column character in which the requested position occurs.
There are no warning indications relative to cursor relocation.
The application should not maintain an image of the cursor position, since
this constitutes placing terminal-specific information in the application and
defeats the purpose of using Curses.
Portable applications cannot assume that a cursor position specified in an
insert function is a reusable indication of the actual cursor position.
Deletion
Deletion functions (such as
delch(3curses))
delete the simple or complex
character at the specified or implied cursor position,
no matter which column of the character this is.
All column positions are replaced by
the background character and rendition and the cursor is not relocated.
Window Operations
Overlapping a window (that is, placing one window on top of another)
and overwriting a window
(that is, copying the contents of one window into another) follows
the operation of overwriting multi-column glyphs around its edge.
Any orphaned columns are handled as in the character operations.
Characters that Straddle the Subwindow Border
A subwindow can be defined such that multi-column characters straddle the
subwindow border. The character operations deal with these straddling
characters as follows:
Reading the subwindow with a function such as
in_wch(3curses)
reads the entire straddling character.
Adding, inserting or deleting in the subwindow deletes the entire straddling
character before the requested operation begins and does not relocate the
cursor.
Scrolling lines in the subwindow has the following effects:
A straddling character at the start of the line is completely erased before
the scroll operation begins.
A straddling character at the end of the line moves in the direction of the
scroll and continues to straddle the subwindow border.
Column positions
outside the subwindow at the straddling character's former position are
orphaned unless another straddling character scrolls into those positions.
If the application calls a function such as
border(3curses),
the above situations do not occur because writing the border on the subwindow
deletes any straddling characters.
In the above cases involving multi-column characters, operations confined to a
subwindow can modify the screen outside the subwindow.
Therefore, saving a
subwindow, performing operations within the subwindow, and then restoring the
subwindow may disturb the appearance of the screen.
To overcome these
effects (for example, for pop-up windows), the application should refresh
the entire screen.
Special Characters
Some functions process special characters as specified below.
In functions that do not move the cursor based on the
information placed in the window, these special characters would only be used
within a string in order to affect the placement of subsequent characters; the
cursor movement specified below does not persist in the visible cursor beyond
the end of the operation. In functions that do move the cursor, these special
characters can be used to affect the placement of subsequent characters and to
achieve movement of the visible cursor.
backspace>
Unless the cursor was already in column 0, <backspace> moves the cursor one
column toward the start of the current line and any characters after the
<backspace> are added or inserted starting there.
<carriage return>
Unless the cursor was already in column 0, <carriage return> moves the cursor
to the start of the current line. Any characters after the <carriage return>
are added or inserted starting there.
<newline>
In an add operation, Curses adds the background character into successive
columns until reaching the end of the line. Scrolling occurs as described in
``Truncation, Wrapping and Scrolling''.
Any characters after the <newline> character are added, starting at the
start of the new line.
In an insert operation, <newline> erases the remainder of the current
line with the background character, effectively a
wclrtoeol(3curses),
and moves the cursor to the start of a new line.
When scrolling is
enabled, advancing the cursor to a new line may cause scrolling as
described in
``Truncation, Wrapping and Scrolling''.
Any characters after the <newline> character are inserted at the
start of the new line.
Tab characters in text move subsequent characters to the next
horizontal tab stop.
By default, tab stops are in columns 0, 8, 16, and so on.
In an insert or add operation, Curses inserts or adds, respectively, the
background character into successive columns until reaching the next tab stop.
If there are no more tab stops in the current line, wrapping and scrolling
occur as described in
``Truncation, Wrapping and Scrolling''.
Control Characters
The Curses functions that perform special-character processing conceptually
convert control characters to the caret ('^') character followed by
a second character (which is an upper-case letter if it is alphabetic) and
write this string to the window in place of the control character. The
functions that retrieve text from the window will not retrieve the original
control character.
Rendition of Characters Placed into a Window
When the application adds or inserts characters into a window, the effect is
as follows:
If the character is not the space character, then the window receives:
the character that the application specifies
the color that the application specifies; or the window color, if the
application does not specify a color
the attributes specified, OR-ed with the window attributes.
If the character is the space character, then the window receives:
the background character
the color that the application specifies; or the window color, if
the application does not specify a color
the attributes specified, OR-ed with the window attributes.
Input Processing
The Curses input model provides a variety of ways to obtain input from the
keyboard.
Keypad Processing
The application can enable or disable
keypad translation
by calling
keypad(3curses).
When translation is enabled, Curses attempts to translate a sequence of
terminal input that represents the pressing of a function key into a single
key code.
When translation is disabled, Curses passes terminal input to the
application without such translation, and any interpretation of the input as
representing the pressing of a keypad key must be done by the application.
The complete set of key codes for keypad keys that Curses can process is
specified by the constants defined in
curses.h whose names begin with KEY_.
Each terminal type described in the terminfo
database may support some or all of these key codes.
The terminfo
database specifies the sequence of input characters from the terminal type
that correspond to each key code (see
terminfo(4)).
The Curses implementation cannot translate keypad keys on terminals where
pressing the keys does not transmit a unique sequence.
When translation is enabled and a character that could be the beginning of a
function key (such as escape) is received, Curses notes the time and begins
accumulating characters.
If Curses receives additional characters that
represent the pressing of a keypad key, within an acceptable interval from
the time the first character was received, then Curses converts this input to
a key code for presentation to the application.
If such characters are not
received during this interval, translation of this input does not occur and
the individual characters are presented to the application separately.
(Because Curses waits for this interval to accumulate a key code, many
terminals experience a delay between the time a user presses the escape key
and the time the escape is returned to the application.)
In addition, No Timeout Mode provides that in any case where Curses has
received part of a function key sequence, it waits indefinitely for the
complete key sequence.
The ``acceptable interval'' in the previous paragraph
becomes infinite in No Timeout Mode.
No Timeout Mode allows the use of
function keys over slow communication lines.
No Timeout Mode lets the user
type the individual characters of a function key sequence, but also delays
application response when the user types a character (not a function key) that
begins a function key sequence. For this reason, in No Timeout Mode many
terminals will appear to hang between the time a user presses the escape key
and the time another key is pressed.
No Timeout Mode is switchable by calling
notimeout(3curses).
If any special characters (see
``Special Characters'')
are defined or redefined to be characters that are members of a function key
sequence, then Curses will be unable to recognise and translate those function
keys.
Several of the modes discussed below are described in terms of availability of
input.
If keypad translation is enabled, then input is not available once
Curses has begun receiving a keypad sequence until the sequence is completely
received or the interval has elapsed.
Input Mode
The general terminal interface defines flow-control characters, the
interrupt character, the erase character, and the kill character (see
termio(7),
under ``Special characters'').
Four mutually-exclusive Curses
modes let the application control the effect of these input characters:
Input Mode
Effect
Cooked Mode
This achieves normal line-at-a-time processing with all special characters
handled outside the application.
This achieves the same effect as canonical-mode input processing
as specified in
termio(7).
The state of the ISIG and IXON flags are not changed upon entering this mode.
The implementation supports erase and kill characters from any supported
locale, no matter what the width of the character is.
cbreak Mode
Characters typed by the user are immediately available to the application
and Curses does not perform special processing on either the erase
character or the kill character.
An application can select cbreak mode to do its own line
editing but to let the abort character be used to abort the task.
This mode achieves the same effect as non-canonical-mode,
Case B input processing (with MIN set to 1 and ICRNL cleared) as specified
in
termio(7).
The state of the ISIG and IXON flags are not changed upon entering this mode.
Half-Delay Mode
The effect is the same as cbreak, except that input functions wait
until a character is available or an interval defined by the application
elapses, whichever comes first.
This mode achieves the same effect as non-canonical-mode,
Case C input processing (with TIME set to the value
specified by the application) as specified in
termio(7).
The state of the ISIG and IXON flags are not changed upon entering this mode.
Raw Mode
Raw mode gives the application maximum control over terminal input.
The application sees each character as it is typed.
This achieves the same effect as non-canonical mode, Case D input
processing as specified in
termio(7).
The ISIG and IXON flags are cleared upon entering this mode.
The terminal interface settings are recorded when the process calls
initscr(3curses)
or
newterm(3curses)
to initialize Curses and restores these settings when
endwin(3curses)
is called.
The initial input mode is cbreak mode.
The behavior of the <BREAK> key depends on other bits in
the display driver that are not set by Curses.
Delay Mode
Two mutually-exclusive delay modes specify how quickly certain Curses
functions return to the application when there is no terminal input waiting
when the function is called:
No Delay
The function fails.
Delay
The application waits until the implementation passes text through to the
application.
If cbreak or Raw Mode is set, this is after one character.
Otherwise, this is after the first <newline> character,
end-of-line character, or end-of-file character.
Echo Processing
Echo mode determines whether Curses echoes typed characters to the screen.
The effect of Echo mode is analogous to the effect of the ECHO flag in the
local mode field of the termios structure associated with the terminal
device connected to the window.
However, Curses always clears the ECHO flag when invoked,
to inhibit the operating system from performing echoing.
The method of echoing characters is not identical to the operating
system's method of echoing characters, because Curses performs additional
processing of terminal input.
If in Echo mode, Curses performs its own echoing: any visible input character
is stored in the current or specified window by the input function that the
application called, at that window's cursor position, as though
addch(3curses)
were called, with all consequent effects such as cursor movement and wrapping.
If not in Echo mode, any echoing of input must be performed by the
application. Applications often perform their own echoing in a controlled
area of the screen, or do not echo at all, so they disable Echo mode.
It may not be possible to turn off echo processing for
synchronous and networked asynchronous terminals
because echo processing is done directly by the
terminals. Applications running on such terminals
should be aware that any characters typed will
appear on the screen at wherever the cursor is
positioned.
The Set of Curses Functions
The Curses functions allow: overall screen, window and pad manipulation;
output to windows and pads; reading terminal input; control over terminal and
Curses input and output options; environment query functions; color
manipulation; use of soft label keys; access to the terminfo
database of terminal capabilities; and access to low-level functions.
Function Name Conventions
The reference manual pages in
Section 3curses manual pages in Section 3curses manual pages
present families of multiple Curses functions.
Most function families have
different functions that give the programmer the following options:
A function with the basic name operates on the window
stdscr.
A function with the same name plus the w prefix operates on a window
specified by the win argument.
When the reference manual page for a function family refers to the
current or specified window, it means stdscr
for the basic functions and the window specified by
win for any w function.
Functions whose names have the p prefix require an argument that is a
pad instead of a window.
A function with the basic name operates based on the current cursor position
(of the current or specified window, as described above).
A function with the same name plus the mv prefix moves the
cursor to a position specified by the y and x
arguments before performing the specified operation.
When the reference manual page for a function family refers to the
current or specified position,
it means the cursor position for the basic functions and the position
(y, x) for any mv function.
The mvw prefix exists and combines the mv
semantics discussed here with the w semantics discussed above.
The window argument is always specified before the coordinates.
A function with the basic name is often provided for historical compatibility
and operates only on single-byte characters.
A function with the same name
plus the w infix operates on wide (multi-byte) characters.
A function with the same name plus the _w infix operates on
complex characters and their renditions.
When a function with the basic name operates on a single character, there is
sometimes a function with the same name plus the n infix that operates
on multiple characters.
An n argument specifies the number of characters to process.
The respective manual page specifies the outcome if
the value of n is inappropriate.
The following notation indicates the effect when characters are moved to the
screen.
(For the Get* functions, this applies only when echoing is enabled.)
Column
Description
s
Y means these functions perform special-character processing (see
``Special Characters''.
N means they do not.
? means the results are unspecified when these
functions are applied to special characters.
A dash (-) means the attribute specified by this column does
not apply to these functions.
w
Y means these functions perform wrapping (see
``Truncation, Wrapping and Scrolling''.
N means they do not.
A dash (-) means the attribute specified by this column does
not apply to these functions.
c
Y means these functions advance the cursor (see
``Truncation, Wrapping and Scrolling''.
N means they do not.
A dash (-) means the attribute specified by this column does
not apply to these functions.
Interfaces Implemented as Macros
The following interfaces with arguments must be implemented as macros.
The relevance to the application programmer is that the ampersand (&)
character cannot be used before the arguments.
The header file reference manual pages list other macros, like COLOR_BLACK,
that do not take arguments.
Initialised Curses Environment
Before executing an application that uses Curses,
the terminal must be prepared as follows:
If the terminal has hardware tab stops, they should be set.
Any initialization strings defined for the terminal must be output to the
terminal.
The resulting state of the terminal must be compatible with the model of the
terminal that Curses has, as reflected in the terminal's entry in the
terminfo
database (see
terminfo(4)).
To initialize Curses, the application must call
initscr(3curses)
or
newterm(3curses)
before calling any of the other functions that deal with windows and
screens, and it must call
endwin(3curses)
before exiting. To get character-at-a-time input
without echoing (most interactive, screen-oriented programs want this), the
following sequence should be used:
initscr
cbreak
noecho
Most programs would additionally use the sequence:
This section indicates to the application writer some considerations to be
borne in mind when driving synchronous, networked asynchronous (NWA) or
non-standard directly-connected asynchronous terminals.
Such terminals are often used in a mainframe environment and communicate to
the host in block mode. That is, the user types characters at the terminal
then presses a special key to initiate transmission of the characters to the
host.
Frequently, although it may be possible to send arbitrary sized blocks to the
host, it is not possible or desirable to cause a character to be
transmitted with only a single keystroke.
This can cause severe problems to an application wishing to make use of
single-character input; see
``Input Processing''.
Output
The Curses interface can be used in the normal way for all operations
pertaining to output to the terminal, with the possible exception that on some
terminals the
refresh(3curses)
routine may have to redraw the entire screen contents in order to perform any
update.
If it is additionally necessary to clear the screen before each such
operation, the result could be undesirable.
Input
Because of the nature of operation of synchronous (block-mode) and NWA
terminals, it might not be possible to support all or any of the Curses
input functions. In particular, the following points should be noted:
Single-character input might not be possible. It may be necessary to press a
special key to cause all characters typed at the terminal to be transmitted to
the host.
It is sometimes not possible to disable echo. Character echo may be performed
directly by the terminal. On terminals that behave in this way, any Curses
application that performs input should be aware that any characters typed will
appear on the screen at wherever the cursor is positioned. This does not
necessarily correspond to the position of the cursor in the window.
Use and Implementation of Curses Interfaces
Each of the following statements applies unless explicitly stated
otherwise in the detailed descriptions that follow.
If an argument to a
function has an invalid value (such as a value outside the domain of the
function, or a pointer outside the address space of the program, or a
null pointer), the behaviour is undefined.
Any function declared in a
header may also be implemented as a macro defined in the header, so a library
function should not be declared explicitly if its header is included.
Any macro definition of a function can be suppressed locally by
enclosing
the name of the function in parentheses, because the name is then not
followed by the left parenthesis that indicates expansion of a macro
function name.
For the same syntactic reason, it is permitted to take
the address of a library function even if it is also defined as a macro.
The use of the C-language #undef
construct to remove any such macro definition
will also ensure that an actual function is referred to.
Any invocation of a library function that is implemented
as a macro will expand to code that evaluates each of its arguments
exactly once, fully protected by parentheses where necessary, so it is
generally safe to use arbitrary expressions as arguments.
Likewise, those function-like macros described in the following sections may be
invoked in an expression anywhere a function with a compatible return
type could be called.
Provided that a library function can be declared without reference to any
type defined in a header, it is also permissible to declare the
function, either explicitly or implicitly, and use it without
including its associated header.
If a function that accepts a variable number of
arguments is not declared (explicitly or by including its associated
header), the behaviour is undefined.
The Compilation Environment
Applications should ensure that the feature test macro
_XOPEN_SOURCE is defined before inclusion of any header.
This is needed to enable the
functionality described in the
Section 3curses manual pages in Section 3curses manual pages
manual pages.
The _XOPEN_SOURCE macro may be defined automatically by the
compilation process, but to ensure maximum portability, applications
should make sure that _XOPEN_SOURCE is defined by using either
compiler options or #define directives in the source files,
before any #include directives.
Identifiers in this document may only be undefined using the
#undef directive as described in
``Use and Implementation of Curses Interfaces''
or
``The X/Open Name Space (ENHANCED CURSES)''.
These #undef directives must follow all
#include directives of any XSI headers.
Most strictly conforming POSIX and ISO C
applications will compile on systems compliant to this specification.
However, an application which uses any of
the items marked as an extension to POSIX and ISO C,
for any purpose other than that shown here, may not compile.
In such cases, it may be necessary to
alter those applications to use alternative identifiers.
Since this document is aligned with the ISO C standard,
and since all functionality enabled by the_POSIX_C_SOURCE
set equal to 2
should be enabled by _XOPEN_SOURCE, there should be no need to
define either _POSIX_SOURCE or _POSIX_C_SOURCE
if _XOPEN_SOURCE is defined.
Therefore if _XOPEN_SOURCE is defined and
_POSIX_SOURCE is defined, or _POSIX_C_SOURCE
is set equal to 1 or 2,
the behaviour is the same as if only _XOPEN_SOURCE is defined.
However should _POSIX_C_SOURCE be set to a value greater than 2,
the behaviour is undefined.
The
c89(1)
and
cc(1)
utilities recognise the additional
-l operand for standard libraries:
-l curses
This operand makes visible all library functions referenced in this
manual page, (except for those labelled ENHANCED CURSES).
If the application defines the _XOPEN_SOURCE_EXTENDED feature test
macro, then -l curses also makes visible all portions of
this specification labelled ENHANCED CURSES.
An application that uses any API specified as
ENHANCED CURSES must define _XOPEN_SOURCE_EXTENDED
equal to ``1'' in each source file or as part of its compilation
environment.
When _XOPEN_SOURCE_EXTENDED is set equal to ``1'' in a
source file, it must appear before any header is included.
The X/Open Name Space (ENHANCED CURSES)
When _XOPEN_SOURCE is defined, each header defines or declares some
identifiers, potentially conflicting with identifiers used by the
application.
The set of identifiers visible to the application consists of
precisely those identifiers from the header pages of the included headers, as
well as additional identifiers reserved for the implementation.
In addition,
some headers may make visible identifiers from other headers as indicated on
the relevant header pages.
The identifiers reserved for use by the implementation are described below.
Each identifier with external linkage described in the header section
is reserved for use as an identifier with external linkage if the
header is included.
Each macro name described in the header section is reserved for
any use if the header is included.
Each identifier with file scope described in the header section is
reserved for use as an identifier with file scope in the same
name space if the header is included.
All identifiers consisting of exactly 2 upper-case letters.
If any header is included, identifiers with the _t
suffix are reserved for any use by the implementation.
If any header in the following table is included, macros with the prefixes
shown may be defined.
After the last inclusion of a given header, an
application may use identifiers with the corresponding prefixes for its own
purpose, provided their use is preceded by an
#undef of the corresponding macro.
The following identifiers are reserved regardless of the inclusion of headers:
All identifiers that begin with an underscore and either an
upper-case letter or another underscore are always reserved for
any use by the implementation.
All identifiers that begin with an underscore are always reserved
for use as identifiers with file scope in both the ordinary
identifier and tag name spaces.
All identifiers listed as reserved in the XSH specification are reserved for use as
identifiers with external linkage.
All the identifiers defined in this document that have external linkage are
always reserved for use as identifiers with external linkage.
No other identifiers are reserved.
Applications must not declare or define identifiers with the same name as an
identifier reserved in the same context. Since macro names are replaced
whenever found, independent of scope and name space, macro names matching any
of the reserved identifier names must not be defined if any associated header
is included.
Headers may be included in any order, and each may be included more than once
in a given scope, with no difference in effect from that of being included
only once.
If used, a header must be included outside of any external declaration
or definition, and it must be first included before the first reference
to any type or macro it defines, or to any function or object it declares.
However, if an identifier is declared or defined
in more than one header, the second and subsequent associated headers
may be included after the initial reference to the identifier.
Prior to the inclusion of a header,
the program must not define any macros with names lexically identical
to symbols defined by that header.
Interfaces Implemented as Macros (ENHANCED CURSES)
The requirements in this section are in effect only for implementations
that claim Enhanced Curses compliance.
The following interfaces with arguments must be implemented as macros. The
relevance to the application programmer is that the `&' character
cannot be used before the arguments.
Most functions provide an error number in
errno
which is either a variable or macro defined in
<errno.h>;
the macro expands to a modifiable
lvalue of type int.
A list of valid values for errno
appears in
Intro(2).
Data Types
All of the data types used by Curses functions are defined by the
implementation. The following list describes these types:
attr_t
An integral type that can contain at least an unsigned short.
The type attr_t is used to hold an OR-ed set of attributes
defined in curses.h that begin with the prefix WA_.
bool
Boolean data type.
chtype
An integral type that can contain at least an unsigned char and attributes.
Values of type chtype are formed by OR-ing together an
unsigned char value and zero or more of the base attribute
flags defined in curses.h that have the A_ prefix.
The application can extract these components of a
chtype value using the base masks defined in
curses.h for this purpose.
The chtype data type also contains a colour-pair.
Values of type chtype are formed by OR-ing together
an unsigned char value, a colour pair, and zero or more of
the attributes defined in curses.h
that begin with the prefix A_.
The application can extract these components
of a chtype value using the masks defined in
curses.h for this purpose.
A type that can reference a string of wide characters of up to an
implementation-dependent length, a colour-pair, and zero or more
attributes from the set of all attributes defined in this document.
A null cchar_t object is an object that references a empty
wide-character string.
Arrays of cchar_t objects are terminated by a
null cchar_t object.