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.\" Author: Thomas E. Dickey 1996-on
.\"
.\" $Id: resizeterm.3,v 1.7 2023/10/17 09:52:08 nicm Exp $
.TH resizeterm 3 2023-07-01 "ncurses 6.4" "Library calls"
.de bP
.ie n  .IP \(bu 4
.el    .IP \(bu 2
..
.SH NAME
\fBis_term_resized\fP,
\fBresize_term\fP,
\fBresizeterm\fP \- change the curses terminal size
.SH SYNOPSIS
\fB#include <curses.h>\fP
.sp
\fBbool is_term_resized(int \fIlines\fB, int \fIcolumns\fB);\fR
.br
\fBint resize_term(int \fIlines\fB, int \fIcolumns\fB);\fR
.br
\fBint resizeterm(int \fIlines\fB, int \fIcolumns\fB);\fR
.SH DESCRIPTION
This is an extension to the curses library.
It provides callers with a hook into the \fBncurses\fP 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:
.bP
Curses windows cannot extend outside the screen.
If the terminal is shrunk, curses windows must be shrunk to fit.
.bP
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.
.PP
If the calling program has not set up a handler for \fBSIGWINCH\fP
when it initializes \fBncurses\fP
(e.g., using \fBinitscr\fP(3) or \fBnewterm\fP(3)),
then \fBncurses\fP sets a handler for \fBSIGWINCH\fP which notifies
the library when a window-size event has occurred.
The library checks for this notification
.bP
when reading input data,
.bP
when implicitly resuming program mode
(e.g., between \fBendwin\fP(3) and \fBwrefresh\fP(3)),
and
.bP
when explicitly resuming program mode in \fBrestartterm\fP(3).
.PP
When the library has found that the terminal's window-size has
changed, it calls \fBresizeterm\fP to update its data structures.
.PP
An application which establishes its own \fBSIGWINCH\fP handler
can call \fBresizeterm\fP, but in that case, the library will not
see \fBSIGWINCH\fP, and proper layout will rely upon the application.
.SH FUNCTIONS
.SS resizeterm
The function \fBresizeterm\fP resizes the standard and current windows
(i.e., \fBstdscr\fP and \fBcurscr\fP)
to the specified dimensions, and adjusts other bookkeeping data used by
the \fBncurses\fP library that record the window dimensions
such as the \fBLINES\fP and \fBCOLS\fP variables.
.SS resize_term
Most of the work for \fBresizeterm\fP is
done by the inner function \fBresize_term\fP.
The outer function \fBresizeterm\fP adds bookkeeping
for the \fBSIGWINCH\fP handler,
as well as repainting the soft-key area (see \fBslk_touch\fP(3)).
.PP
The \fBresize_term\fP function attempts to resize all windows.
This helps with simple applications.
However:
.bP
It is not possible to automatically resize pads.
.bP
Applications which have complicated layouts should check for
\fBKEY_RESIZE\fP returned from \fBwgetch\fP,
and adjust their layout, e.g., using \fBwresize\fP and \fBmvwin\fP,
or by recreating the windows.
.PP
When resizing windows, \fBresize_term\fP 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, \fBresize_term\fP will keep the window
extending to the corresponding limit, regardless of whether the
screen has shrunk or grown.
.SS is_term_resized
A support function \fBis_term_resized\fP is provided so that applications
can check if the \fBresize_term\fP function would modify the window structures.
It returns \fBTRUE\fP if the windows would be modified,
and \fBFALSE\fP otherwise.
.SH RETURN VALUE
Except as noted, these functions return
the integer \fBERR\fP upon failure and \fBOK\fP 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.
.SH NOTES
While these functions are intended to be used to support a signal handler
(i.e., for \fBSIGWINCH\fP), care should be taken to avoid invoking them in a
context where \fBmalloc\fP or \fBrealloc\fP may have been interrupted,
since it uses those functions.
.PP
If ncurses is configured to supply its own \fBSIGWINCH\fP handler,
.bP
on receipt of a \fBSIGWINCH\fP, the handler sets a flag
.bP
which is tested in
\fBwgetch\fP(3),
\fBdoupdate\fP(3) and
\fBrestartterm\fP(3),
.bP
in turn, calling the \fBresizeterm\fP function,
.bP
which \fBungetch\fP's a \fBKEY_RESIZE\fP which
will be read on the next call to \fBwgetch\fP.
.IP
The \fBKEY_RESIZE\fP alerts an application that the screen size has changed,
and that it should repaint special features such as pads that cannot
be done automatically.
.IP
Calling \fBresizeterm\fP or \fBresize_term\fP
directly from a signal handler is unsafe.
This indirect method is used to provide a safe way to resize the ncurses
data structures.
.PP
If the environment variables \fBLINES\fP or \fBCOLUMNS\fP are set,
this overrides the library's use of the window size obtained from
the operating system.
Thus, even if a \fBSIGWINCH\fP is received,
no screen size change may be recorded.
.SH PORTABILITY
It is possible to resize the screen with SVr4 curses,
by
.bP
exiting curses with \fBendwin\fP(3) and
.bP
resuming using \fBrefresh\fP(3).
.PP
Doing that clears the screen and is visually distracting.
.PP
This extension of ncurses was introduced in mid-1995.
It was adopted in NetBSD curses (2001) and PDCurses (2003).
.SH SEE ALSO
\fBcurs_getch\fP(3),
\fBcurs_variables\fP(3),
\fBwresize\fP(3).
.SH AUTHOR
Thomas Dickey (from an equivalent function written in 1988 for BSD curses).