Ubuntu Manpage: scr_dump, scr_restore, scr_init, scr_set - read/write a curses screen from/to a file

name
synopsis
description
return value
notes
portability
history
see also

Provided by: ncurses-doc_6.5+20250216-1_all

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 preceding 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 subsection “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 inheritance 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 filename 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 structures.  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.