DOKK / manpages / debian 10 / ncurses-doc / resize_term.3ncurses.en
resizeterm(3NCURSES) resizeterm(3NCURSES)

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).

The function resizeterm resizes the standard and current windows 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 is done by the inner function resize_term. The outer function resizeterm adds bookkeeping for the SIGWINCH handler. When resizing the windows, resize_term blank-fills the areas that are extended. The calling application should fill in these areas with appropriate data. The resize_term function attempts to resize all windows. However, due to the calling convention of pads, it is not possible to resize these without additional interaction with the application.

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,

  • on receipt of a SIGWINCH, the handler sets a flag
  • which is tested in wgetch(3X) and doupdate,
  • 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).

getch(3NCURSES), curses_variables(3NCURSES), wresize(3NCURSES).

Thomas Dickey (from an equivalent function written in 1988 for BSD curses).