---
name: "bool"
section: "3ncurses"
platform: "linux"
package: "ncurses-doc"
version: "6.5+20250216-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/curses_variables"
---

# bool(3ncurses)

curses data types, constants, and global variables

Part of [curses\_variables(3ncurses)](/curses_variables/3ncurses.md).

## NAME

*bool*, *chtype*, *cchar\_t*, *attr\_t*, *SCREEN*, *WINDOW*, **TRUE**, **FALSE**, **ERR**, **OK**, **CCHARW\_MAX**, **curscr**, **newscr**, **stdscr**, **COLORS**, **COLOR\_PAIRS**, **COLS**, **LINES**, **ESCDELAY**, **TABSIZE** - *curses* data types, constants, and global variables

## SYNOPSIS

```
#include <curses.h>
```

*/\* data types \*/* **typedef** */\** **...** *\*/* **bool;** **typedef** */\** **...** *\*/* **chtype;** **typedef** */\** **...** *\*/* **cchar\_t;** **typedef** */\** **...** *\*/* **attr\_t;** **typedef** */\** **...** *\*/* **SCREEN;** **typedef** */\** **...** *\*/* **WINDOW;**

*/\* constants \*/* **const bool TRUE;** **const bool FALSE;**

**const** */\** **...** *\*/* **ERR;** **const** */\** **...** *\*/* **OK;**

*/\* extension \*/* **const** */\** **...** *\*/* **CCHARW\_MAX;**

*/\* variables \*/* **int COLORS;** **int COLOR\_PAIRS;** **int COLS;** **int LINES;** **WINDOW \* curscr;** **WINDOW \* stdscr;**

*/\* extensions \*/* **int ESCDELAY;** **int TABSIZE;** **WINDOW \* newscr;**

## DESCRIPTION

**This page summarizes data types,** **constants,** **and variables provided by the** *curses* **library.** **Locate further discussion in ncurses(3NCURSES).**

**Depending on** *ncurses***'s build-time configuration,** **the variables may instead be** **macros (see threads(3NCURSES) and opaque(3NCURSES))** **that provide read-only access to the library's state.** **In either case,** **applications should treat them as read-only to avoid** **confusing the library.**

## CONSTANTS

### TRUE, FALSE

**The** *curses* **library defines TRUE and FALSE** **to represent the values of the Boolean data type.**

### ERR, OK

*curses* **and** *terminfo* **routines frequently return these** **constant integral values indicating failure and success,** **respectively.**

### CCHARW\_MAX

**This integral value,** **an** *ncurses* **extension,** **contains the maximum number of** *wchar\_t* **wide characters that can be stored in a** *curses* **complex character** *cchar\_t*.

## PREDEFINED TYPES

### *bool*

**X/Open Issue 4** *curses* **(1996) preceded the ISO C99 and ISO C++98** **standards,** **each of which also defined a Boolean data type.** **The** *curses* **library requires an integral type** *bool***.**

**ncurses' configure script attempts to discover the** **data type used by the system's C and C++ compilers,** **to reuse for the** *curses* *bool***.**

### *chtype*

**The** *chtype* **integral type combines a** **(“narrow”,** **8-bit)** **character with attributes encoding the character's** *rendition***,** **such as the styling of its typeface and/or foreground and background** **colors.** **See,** **for example,** **addch(3NCURSES),** **attron(3NCURSES),** **and** **inch(3NCURSES).**

### *cchar\_t*, *attr\_t*

*chtype* **is too small for the standard C library's wide-character** **type,** *wchar\_t***.** *cchar\_t* **is a type that can accommodate an** *attr\_t* **and** **enough wide characters to store what Unicode terms a** *grapheme cluster* **(a “user-perceived character” \[UAX #29\],** **which may nevertheless require several character encoding units to** **represent).** *attr\_t* **is an integral type storing “wide” attributes that** **apply to** *cchar\_t***s.** **See,** **for example,** **add\_wch(3NCURSES),** **attr\_on(3NCURSES),** **and** **in\_wch(3NCURSES).**

### *SCREEN*

*curses* **manages a terminal device with this structure type;** **see initscr(3NCURSES).**

### *WINDOW*

*curses* **represents rectangular portions of the terminal screen with the** *WINDOW* **structure type;** **see subsection “Overview” of ncurses(3NCURSES).**

## VARIABLES

### curscr, newscr, stdscr

**When a** *curses* **application calls** **initscr(3NCURSES) or newterm(3NCURSES),** **the library creates a window named** **stdscr** **that is the same size as the terminal screen** **and is the implicit window used by functions** **that interact with a window** **but do not take a parameter identifying one;** **many** *curses* **functions use it.** **An application need not use** **stdscr**; **it might prefer to tile the display into multiple windows instead.**

**The library records updates to the terminal screen in a window named** **curscr.** **This object is referred to as the “physical screen” in** **refresh(3NCURSES) and** **outopts(3NCURSES).**

*ncurses* **collects pending updates to the terminal screen in a** **window named newscr.** **This object is referred to as the “virtual screen” in the** **kernel(3NCURSES),** **refresh(3NCURSES),** **and** **outopts(3NCURSES).** **When the screen is refreshed,** *curses* **determines a minimal set of updates using the terminal's** **capabilities to make curscr look like newscr.**

### COLORS

**Once** *curses* **is initialized,** **COLORS** **contains the number of colors supported by the terminal;** **see color(3NCURSES).**

### COLOR\_PAIRS

**Once** *curses* **is initialized,** **COLOR\_PAIRS** **contains the number of color pairs supported by the terminal;** **see color(3NCURSES).**

### COLS, LINES

**Once** *curses* **is initialized,** **COLS** **and** **LINES** **contain the screen's width and height in character cells,** **respectively;** **that is,** **the number of columns and lines.**

### ESCDELAY

**For** *curses* **to distinguish the ESC character resulting from a user's press of the** **“Escape” key on the input device from one beginning an** *escape sequence* **(as commonly produced by function keys),** **it waits after the escape character to see if further characters are** **available on the input stream within a short interval.** **ESCDELAY** **stores this interval in milliseconds.**

**If keypad(3NCURSES) is disabled for the** *curses* **window receiving input,** **a program must disambiguate escape sequences itself.**

### TABSIZE

**The** *curses* **library converts a tab character to this number of** **spaces as it adds a tab to a window;** **see addch(3NCURSES).**

## NOTES

**Either initscr(3NCURSES) or newterm(3NCURSES) initializes** *curses***.**

**If** *ncurses* **is configured to provide separate** *curses* **and** *tinfo* **libraries,** **most of these symbols reside in the former.** **The** **bool** **data type** **is used by both.**

## EXTENSIONS

**The** **CCHARW\_MAX** **constant,** **and** **ESCDELAY**, **TABSIZE**, **and** **newscr** **variables,** **are** **extensions,** **the first of these originating in** *ncurses*.

## PORTABILITY

**Applications employing** *ncurses* **extensions should condition their use on the visibility of the** **NCURSES\_VERSION** **preprocessor macro.**

**The X/Open Curses standard documents all of the foregoing types and** **symbols except for** **CCHARW\_MAX**, **newscr**, **TABSIZE**, **and** **ESCDELAY**.

**X/Open Curses describes curscr only as “an internal data** **structure”;** **SVr4 gave more details,** **noting its use “for certain low-level operations like clearing and** **redrawing a screen containing garbage”.** **Neither specified its interaction with the rest of the interface beyond** **use as an argument to clearok(3NCURSES) and wrefresh(3NCURSES).**

**newscr is a feature of SVr4** *curses***.** **When refreshing the screen,** **it is used as a working area for combining the standard window** **stdscr with any others the application may have created with** **newwin(3NCURSES).** **When the update of newscr is complete,** *curses* **modifies curscr to match newscr.**

**TABSIZE is a feature of SVr4** *curses***.**

- •

  **SVr4 initially sets TABSIZE from the terminal description's** **init\_tabs capability.** **After that,** **it can be altered by applications using SVr4** *curses***.**

- •

  **SVr4** *curses* **uses the value of TABSIZE to compute the** **position of tab stops when updating both** **the virtual screen with addch(3NCURSES) and** **the physical screen with mvcur(3NCURSES).**

- •

  *ncurses* **uses the value of TABSIZE only to update the** **virtual screen.** **It uses the terminal description's “it”** **(init\_tabs) capability for computing hardware tabs** **(that is,** **tab stops on the physical screen).**

- •

  **Other implementations differ.** **For instance,** **NetBSD** *curses* **allows TABSIZE to be set through an** **environment variable.** *ncurses* **does not.**

-

  **NetBSD** *curses* **does not support hardware tabs;** **it uses the init\_tabs capability and the TABSIZE** **variable only for updating the virtual screen.**

**ESCDELAY is a feature of AIX** *curses***.**

- •

  **In AIX,** **the units for ESCDELAY are** *fifths* **of milliseconds.**

- •

  **The default value for AIX's ESCDELAY equals 0.1 seconds.**

- •

  **AIX also enforces a limit of 10,000 seconds for ESCDELAY;** *ncurses* **does not enforce any upper limit.**

*ncurses* **has long used ESCDELAY with units of** **milliseconds,** **making it impossible to be completely compatible with AIX.** **Consequently,** **most users have decided either to override the value,** **or to rely upon its default.**

## SEE ALSO

**\[UAX #29\] “Unicode Standard Annex #29: Unicode Text** **Segmentation”** ⟨https://\\:unicode\\:.org/\\:reports/\\:tr29/⟩

**getcchar(3NCURSES)** **further discusses** **CCHARW\_MAX**.

**ncurses(3NCURSES),** **color(3NCURSES),** **opaque(3NCURSES),** **terminfo(3NCURSES),** **threads(3NCURSES),** **terminfo\_variables(3NCURSES),** **[terminfo(5)](/terminfo/5.md)**