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This is a description of how to actually use the screen package.  In it, we
assume all updating, reading, etc.  is applied to All instructions will work
on any window, with changing the function name and parameters as mentioned
above.  In order to use the screen package, the routines must know about
terminal characteristics, and the space for and must be allocated.  These
functions are performed by Since it must allocate space for the windows, it
can overflow core when attempting to do so.  On this rather rare occasion,
returns ERR.  must be called before any of the routines which affect windows
are used.  If it is not, the program will core dump as soon as either or are
referenced.  However, it is usually best to wait to call it until after you
are sure you will need it, like after checking for startup errors.  Terminal
status changing routines like and should be called after Now that the screen
windows have been allocated, you can set them up for the run.  If you want to,
say, allow the window to scroll, use If you want the cursor to be left after
the last change, use If this isn't done, will move the cursor to the window's
current  after updating it.  New windows of your own can be created, too, by
using the functions and will allow you to get rid of old windows.  If you wish
to change the official size of the terminal by hand, just set the variables
and to be what you want, and then call This is best done before, but can be
done either before or after, the first call to as it will always delete any
existing and/or before creating new ones.  Now that we have set things up, we
will want to actually update the terminal.  The basic functions used to change
what will go on a window are and adds a character at the current , returning
ERR if it would cause the window to illegally scroll, printing a character in
the lower right-hand corner of a terminal which automatically scrolls if
scrolling is not allowed.  changes the current  to whatever you want them to
be.  It returns ERR if you try to move off the window when scrolling is not
allowed.  As mentioned above, you can combine the two into to do both things
in one fell swoop.  The other output functions, such as and all call to add
characters to the window.  After you have put on the window what you want
there, when you want the portion of the terminal covered by the window to be
made to look like it, you must call In order to optimize finding changes,
assumes that any part of the window not changed since the last of that window
has not been changed on the terminal, that you have not refreshed a portion of
the terminal with an overlapping window.  If this is not the case, the
routines and are provided to make it look like a desired part of window has
been changed, thus forcing check that whole subsection of the terminal for
changes.  If you call with it will make the screen look like thinks it looks
like.  This is useful for implementing a command which would redraw the screen
in case it get messed up.  Input is essentially a mirror image of output.  The
complementary function to is which, if echo is set, will call to echo the
character.  Since the screen package needs to know what is on the terminal at
all times, if characters are to be echoed, the tty must be in raw or cbreak
mode.  If it is not, sets it to be cbreak, and then reads in the character.
All sorts of fun functions exists for maintaining and changing information
about the windows.  For the most part, the descriptions in section 5.4. should
suffice.  In order to do certain optimizations, and, on some terminals, to
work at all, some things must be done before the screen routines start up.
These functions are performed in and which are called by In order to clean up
after the routines, the routine is provided.  It restores tty modes to what
they were when was first called.  Thus, anytime after the call to initscr,
should be called before exiting.

                               October 27, 2016                             ()

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