---
name: "bool"
section: "3x"
platform: "linux"
package: "ncurses"
version: "6.6-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/curs_variables/3x"
---

# bool(3x)

curses data types, constants, and global variables

Part of [curs\_variables(3x)](/curs_variables/3x.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 curses(3X).**

**Depending on** *ncurses***'s build-time configuration,** **the variables may instead be** **macros (see curs\_threads(3X) and curs\_opaque(3X))** **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* **functions frequently return these constant integral values** **indicating failure and success,** **respectively.**

### CCHARW\_MAX

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

## DATA TYPES

### *bool*

*curses* **defines an integral type** *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 of the same name.**

*ncurses*'s **configure script attempts to discover the** **data type used by the system's C and C++ compilers,** **to reuse them as its own** *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(3X),** **attron(3X),** **and** **inch(3X).**

### *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(3X),** **attr\_on(3X),** **and** **in\_wch(3X).**

### *SCREEN*

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

### *WINDOW*

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

## VARIABLES

### curscr, newscr, stdscr

**When a** *curses* **application calls** **initscr(3X) or newterm(3X),** **the library creates a window named** **stdscr** **that is the same size as the terminal screen,** **(minus any lines reserved by** **ripoffline(3X) or slk\_init(3X))** **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** **curs\_refresh(3X) and** **curs\_outopts(3X).**

*ncurses* **collects pending updates to the terminal screen in a** **window named newscr.** **This object is referred to as the “virtual screen” in the** **curs\_kernel(3X),** **curs\_refresh(3X),** **and** **curs\_outopts(3X).** **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 a** *curses* **screen is initialized,** **COLORS** **contains the number of colors supported by the terminal;** **see curs\_color(3X).**

### COLOR\_PAIRS

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

### COLS, LINES

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

### ESCDELAY

**When reading key strokes from a window in keypad mode,** *curses* **distinguishes the ESC character resulting from a user's press of the** **“Escape” key on the input device** **from one beginning an escape sequence** **(commonly produced by function keys),** **by waiting after receiving 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(3X) 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 curs\_addch(3X).**

## NOTES

**Initialize a** *curses* **screen with either initscr(3X) or newterm(3X).**

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

## 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(3X) and wrefresh(3X).**

**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(3X).** **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** (**it**) **capability.** **After that,** **it can be altered by applications using SVr4** *curses*.

- •

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

- •

  **In** *ncurses*, **TABSIZE**'s **value affects only the virtual screen.** **The library uses the terminal type description's** **init\_tabs** (**it**) **capability to compute 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** (**it**) **capability and the** **TABSIZE** **variable only to update the virtual screen.**

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

- •

  **AIX treats** **ESCDELAY**'s **value as counting** *fifths* **of milliseconds.**

- •

  **AIX's default** **ESCDELAY** **equals 0.1 seconds.**

- •

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

*ncurses* **has long interpreted** **ESCDELAY** **as a count 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(3X)** **further discusses the** *ncurses* **extension** **CCHARW\_MAX**.

**curses(3X),** **curs\_color(3X),** **curs\_opaque(3X),** **curs\_terminfo(3X),** **curs\_threads(3X),** **term\_variables(3X),** **[terminfo(5)](/terminfo/5.md)**