is_term_resized, resize_term, resizeterm - change the
curses terminal size
bool is_term_resized(int lines, int
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:
int resize_term(int lines, int columns);
int resizeterm(int lines, int columns);
- 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 attributes of the
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
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
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., using wresize and mvwin, or by recreating the
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
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
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
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
If ncurses is configured to supply its own SIGWINCH
- on receipt of a SIGWINCH, the handler sets a flag
- which is tested in wgetch(3X), doupdate(3X) and
- 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
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
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).
Thomas Dickey (from an equivalent function written in 1988 for BSD curses).