scr_dump(3NCURSES) Library calls scr_dump(3NCURSES)
NAME
scr_dump, scr_restore, scr_init, scr_set - read/write a curses screen
from/to a file
SYNOPSIS
#include <curses.h>
int scr_dump(const char * filename);
int scr_restore(const char * filename);
int scr_init(const char * filename);
int scr_set(const char * filename);
DESCRIPTION
curses provides applications the ability to write the contents of the
screen to a file and read them back. To read/write a window (rather
than the whole screen) from/to a file, use getwin(3NCURSES) and
putwin(3NCURSES), respectively.
scr_dump
scr_dump writes to filename the contents of the virtual screen; see
curscr(3NCURSES).
scr_restore
scr_restore updates the virtual screen to match the contents of filename
(if validly written with scr_dump). curses does not perform a refresh;
after making any desired changes, call doupdate(3NCURSES) or similar.
scr_init
scr_init reads filename, using it to initialize curses data structures
describing the state of the terminal screen. curses then, if it decides
the terminal state is valid, bases its next update of the screen on this
information rather than clearing it and starting from scratch.
curses regards the terminal as in an invalid state for computation of
updates based on the contents of filename if
• curses knows that the terminal has been written to since the preced-
ing scr_dump call, or
• the terminal type supports the terminfo capabilities exit_ca_mode
(rmcup) or non_rev_rmcup (nrrmc).
Either of the foregoing conditions means that curses cannot assume that
the terminal's contents match their representation in filename. The
former is due to terminal features (such as xterm(1)'s “alternate
screen”) that couple cursor-positioning mode with a local cache of
screen contents. curses cannot know whether the terminal is displaying
from that local cache at the time the application calls scr_init, so it
makes a pessimistic assumption that a full redraw is required; see sub-
section “Cursor Motions” of terminfo(5).
scr_init could be used after initscr(3NCURSES) or system(3) to share the
screen with another process that has done a scr_dump after
endwin(3NCURSES). An application that supports suspending its state on
exit and subsequent resumption upon later execution might use scr_dump
and scr_init thus.
scr_set
scr_set combines scr_restore and scr_init, synchronizing the contents of
filename with the virtual screen. It can be regarded as a screen inher-
itance function; consider a real-time screen-sharing application.
RETURN VALUE
These functions return OK on success and ERR on failure.
In ncurses, each function returns ERR if it cannot open filename.
scr_init, scr_restore, and scr_set return ERR if the contents of file-
name are invalid.
NOTES
scr_init, scr_restore, and scr_set may be implemented as macros.
PORTABILITY
X/Open Curses Issue 4 describes these functions. It specifies no error
conditions for them.
SVr4 omitted the const qualifiers.
SVr4 documentation describes scr_init such that the dump data is also
considered invalid “if the time-stamp of the tty is old” but does not
define “old”.
As of 2024, PDCurses provides these functions. NetBSD curses does not.
Other implementations of curses store the window in binary form, which
makes the dump dependent upon the curses library's internal data struc-
tures. ncurses avoids this drawback by storing the dump in textual
form, allowing more flexible use of the data. For instance, the
scr_restore of SVr4 curses requires that the dumped window have the same
dimensions as the restored window. ncurses uses its wresize(3NCURSES)
extension to adjust the restored window size.
HISTORY
SVr3 (1987) introduced scr_dump, scr_init, and scr_restore. SVr3.1
added scr_set.
SEE ALSO
ncurses(3NCURSES), initscr(3NCURSES), refresh(3NCURSES), util(3NCURSES),
system(3), scr_dump(5), terminfo(5), wresize(3NCURSES)
ncurses 6.5 2025-01-18 scr_dump(3NCURSES)
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