resizeterm(3x) resizeterm(3x)
is_term_resized, resize_term, resizeterm - change the curses terminal
size
#include <curses.h>
bool is_term_resized(int lines, int columns);
int resize_term(int lines, int columns);
int resizeterm(int lines, int columns);
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
programs running in an X Window terminal (e.g., xterm) when the
terminal's screen size is changed by the user:
o Curses windows cannot extend outside the screen. If the terminal
is shrunk, curses windows must be shrunk to fit.
o If the terminal is stretched, rows and/or columns can be added to
existing windows. The added cells should match the current
attributes of the windows.
If the calling program has not set up a handler for SIGWINCH when it
initializes ncurses (e.g., using initscr(3x) or newterm(3x)), then
ncurses sets a handler for SIGWINCH which notifies the library when a
window-size event has occurred. The library checks for this
notification
o when reading input data,
o when implicitly resuming program mode (e.g., between endwin(3x) and
wrefresh(3x)), and
o when explicitly resuming program mode in restartterm(3x).
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.
The function resizeterm resizes the standard and current windows (i.e.,
stdscr and curscr) to the specified dimensions, and adjusts other
bookkeeping data used by the ncurses library that record the window
dimensions such as the LINES and COLS variables.
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(3x)).
The resize_term function attempts to resize all windows. This helps
with simple applications. However:
o It is not possible to automatically resize pads.
o Applications which have complicated layouts should check for
KEY_RESIZE returned from wgetch, and adjust their layout, e.g.,
using wresize and mvwin, or by recreating the windows.
When resizing windows, resize_term recursively adjusts subwindows,
keeping them within the updated parent window's limits. If a top-level
window happens to extend to the screen's limits, then on resizing the
window, resize_term will keep the window extending to the corresponding
limit, regardless of whether the screen has shrunk or grown.
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.
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.
While these functions are intended to be used to support a signal
handler (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,
o on receipt of a SIGWINCH, the handler sets a flag
o which is tested in wgetch(3x), doupdate(3x) and restartterm(3x),
o in turn, calling the resizeterm function,
o 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
resize 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.
It is possible to resize the screen with SVr4 curses, by
o exiting curses with endwin(3x) and
o resuming using refresh(3x).
Doing that clears the screen and is visually distracting.
This extension of ncurses was introduced in mid-1995. It was adopted
in NetBSD curses (2001) and PDCurses (2003).
curs_getch(3x), curs_variables(3x), wresize(3x).
Thomas Dickey (from an equivalent function written in 1988 for BSD
curses).
resizeterm(3x)