resizeterm 3x 2024-03-16 ncurses 6.5 Library calls

resizeterm(3x)                   Library calls                  resizeterm(3x)


       is_term_resized,   resize_term,   resizeterm   -  manage  the  terminal
       dimensions understood by curses


       #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

       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

       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

           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).


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


       curs_getch(3x), curs_variables(3x), wresize(3x)

ncurses 6.5                       2024-03-16                    resizeterm(3x)