Scroll to navigation

curses_variables(3NCURSES) curses_variables(3NCURSES)

NAME

COLORS, COLOR_PAIRS, COLS, ESCDELAY, LINES, TABSIZE, curscr, newscr, stdscr - curses global variables

SYNOPSIS

#include <curses.h>
int COLOR_PAIRS;


int COLORS;


int COLS;


int ESCDELAY;


int LINES;


int TABSIZE;


WINDOW * curscr;


WINDOW * newscr;


WINDOW * stdscr;

DESCRIPTION

This page summarizes variables provided by the curses library. A more complete description is given in the ncurses(3NCURSES) manual page.

Depending on the configuration, these may be actual variables, or macros (see threads(3NCURSES) and opaque(3NCURSES)) which provide read-only access to curses's state. In either case, applications should treat them as read-only to avoid confusing the library.

COLOR_PAIRS

After initializing curses, this variable contains the number of color pairs which the terminal can support. Usually the number of color pairs will be the product COLORS*COLORS, however this is not always true:

  • a few terminals use HLS colors, which do not follow this rule
  • terminals supporting a large number of colors are limited by the number of color pairs that can be represented in a signed short value.

COLORS

After initializing curses, this variable contains the number of colors which the terminal can support.

COLS

After initializing curses, this variable contains the width of the screen, i.e., the number of columns.

ESCDELAY

This variable holds the number of milliseconds to wait after reading an escape character, to distinguish between an individual escape character entered on the keyboard from escape sequences sent by cursor- and function-keys (see curses(3X)).

LINES

After initializing curses, this variable contains the height of the screen, i.e., the number of lines.

TABSIZE

This variable holds the number of columns used by the curses library when converting a tab character to spaces as it adds the tab to a window (see addch(3NCURSES).

The Current Screen

This implementation of curses uses a special window curscr to record its updates to the terminal screen.

This is referred to as the “physical screen” in the refresh(3NCURSES) and outopts(3NCURSES) manual pages.

The New Screen

This implementation of curses uses a special window newscr to hold updates to the terminal screen before applying them to curscr.

This is referred to as the “virtual screen” in the kernel(3NCURSES), refresh(3NCURSES) and outopts(3NCURSES) manual pages.

The Standard Screen

Upon initializing curses, a default window called stdscr, which is the size of the terminal screen, is created. Many curses functions use this window.

NOTES

The curses library is initialized using either initscr(3X), or newterm(3X).

If curses is configured to use separate curses/terminfo libraries, most of these variables reside in the curses library.

PORTABILITY

TABSIZE is a feature of SVr4 curses which is not documented by X/Open curses.

•
In SVr4 curses, TABSIZE is initially set from the terminal description's init_tabs capability. After that, it can be altered by the applications using SVr4 curses.
SVr4 curses uses the current value of TABSIZE to compute the position of tabstops for updating both the virtual screen with addch(3X) as well as the physical screen with mvcur(3X).
  • This implementation uses the current value of TABSIZE only for updating the virtual screen. It uses the terminal description's it (init_tabs) capability for computing hardware tabs (i.e., tab stops on the physical screen).
  • Other implementations differ. For instance, NetBSD curses allows TABSIZE to be set through an environment variable. This implementation 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 an extension in AIX curses:

  • In AIX, the units for ESCDELAY are fifths of a millisecond.
  • The default value for AIX's ESCDELAY is 0.1 seconds.
  • AIX also enforces a limit of 10,000 seconds for ESCDELAY; this implementation currently has no upper limit.

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

SEE ALSO

ncurses(3NCURSES), opaque(3NCURSES), terminfo(3NCURSES), threads(3NCURSES), terminfo_variables(3NCURSES), terminfo(5).