resizeterm(3NCURSES) Library calls resizeterm(3NCURSES)
NAME
is_term_resized, resize_term, resizeterm - manage the terminal dimen-
sions understood by curses
SYNOPSIS
#include <curses.h>
bool is_term_resized(int lines, int columns);
int resize_term(int lines, int columns);
int resizeterm(int lines, int columns);
DESCRIPTION
This is an extension to the curses library. It provides callers with a
hook into the ncurses data to resize windows, primarily for use by pro-
grams running in an X Window terminal (e.g., xterm) when the terminal's
screen size is changed by the user:
• curses windows cannot extend outside the screen. If the terminal is
shrunk, curses windows must be shrunk to fit.
• If the terminal is stretched, rows and/or columns can be added to
existing windows. The added cells should match the current attrib-
utes of the windows.
If the calling program has not set up a handler for SIGWINCH when it
initializes ncurses (e.g., using initscr(3NCURSES) or
newterm(3NCURSES)), then ncurses sets a handler for SIGWINCH which noti-
fies the library when a window-size event has occurred. The library
checks for this notification
• when reading input data,
• when implicitly resuming program mode (e.g., between
endwin(3NCURSES) and wrefresh(3NCURSES)), and
• when explicitly resuming program mode in restartterm(3NCURSES).
When the library has found that the terminal's window-size has changed,
it calls resizeterm to update its data structures.
An application which establishes its own SIGWINCH handler can call
resizeterm, but in that case, the library will not see SIGWINCH, and
proper layout will rely upon the application.
FUNCTIONS
resizeterm
The function resizeterm resizes the standard and current windows (i.e.,
stdscr and curscr) to the specified dimensions, and adjusts other book-
keeping data used by the ncurses library that record the window dimen-
sions such as the LINES and COLS variables.
resize_term
Most of the work for resizeterm is done by the inner function
resize_term. The outer function resizeterm adds bookkeeping for the
SIGWINCH handler, as well as repainting the soft-key area (see
slk_touch(3NCURSES)).
The resize_term function attempts to resize all windows. This helps
with simple applications. However:
• It is not possible to automatically resize pads.
• Applications which have complicated layouts should check for
KEY_RESIZE returned from wgetch, and adjust their layout, e.g., us-
ing wresize and mvwin, or by recreating the windows.
When resizing windows, resize_term recursively adjusts subwindows, keep-
ing them within the updated parent window's limits. If a top-level win-
dow happens to extend to the screen's limits, then on resizing the win-
dow, resize_term will keep the window extending to the corresponding
limit, regardless of whether the screen has shrunk or grown.
is_term_resized
A support function is_term_resized is provided so that applications can
check if the resize_term function would modify the window structures.
It returns TRUE if the windows would be modified, and FALSE otherwise.
RETURN VALUE
Except as noted, these functions return the integer ERR upon failure and
OK on success. They will fail if either of the dimensions are less than
or equal to zero, or if an error occurs while (re)allocating memory for
the windows.
NOTES
While these functions are intended to be used to support a signal han-
dler (i.e., for SIGWINCH), care should be taken to avoid invoking them
in a context where malloc or realloc may have been interrupted, since it
uses those functions.
If ncurses is configured to supply its own SIGWINCH handler,
• on receipt of a SIGWINCH, the handler sets a flag
• which is tested in wgetch(3NCURSES), doupdate(3NCURSES) and
restartterm(3NCURSES),
• in turn, calling the resizeterm function,
• which ungetch's a KEY_RESIZE which will be read on the next call to
wgetch.
The KEY_RESIZE alerts an application that the screen size has
changed, and that it should repaint special features such as pads
that cannot be done automatically.
Calling resizeterm or resize_term directly from a signal handler is
unsafe. This indirect method is used to provide a safe way to re-
size the ncurses data structures.
If the environment variables LINES or COLUMNS are set, this overrides
the library's use of the window size obtained from the operating system.
Thus, even if a SIGWINCH is received, no screen size change may be
recorded.
PORTABILITY
It is possible to resize the screen with SVr4 curses, by
• exiting curses with endwin(3NCURSES) and
• resuming using refresh(3NCURSES).
Doing that clears the screen and is visually distracting.
ncurses introduced this extension in mid-1995. NetBSD curses adopted it
in 2001 and PDCurses in 2003.
AUTHORS
Thomas Dickey (from an equivalent function written in 1988 for BSD
curses)
SEE ALSO
getch(3NCURSES), curses_variables(3NCURSES), wresize(3NCURSES)
ncurses 6.5 2024-12-28 resizeterm(3NCURSES)
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