This  is a description of how to actually use the screen package.
For simplicity, we assume all updating, reading, etc.  is applied
to  although  a  different window can of course be specified.  In
order to use the screen package, the  routines  must  know  about
terminal  characteristics, and the space for and must be allocat-
ed.  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  ref-
erenced.   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 After the initial window  allocation  done
by  specific window characteristics can be set.  Scrolling can be
enabled by calling 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.  Additional windows  can  be
created  by  using  the functions and allows you to delete an ex-
isiting window.  The variables and control the size of the termi-
nal.  They are initially implicitly set by but can be altered ex-
plicitly by the user followed by a call to Note that any call  to
will  always  delete any existing and/or before creating new ones
so this change is best done before the initial call to 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  win-
dow.  As mentioned above, you can combine the two into to do both
things in one call.  The other output functions (such as and  all
call  to  add  characters to the window.  After a change has been
made to the window, you must call when you want  the  portion  of
the terminal covered by the window to reflect the change.  In or-
der 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  de-
sired part of window has been changed, thus forcing to check that
whole subsection of the terminal for changes.  If you  call  with
it will make the screen look like the image of This is useful for
implementing a command which would redraw the screen in  case  it
got  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.  In  order
to perform 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.
The terminal state module uses the variable to save the  original
terminal  state  which is then restored upon a call to Thus, any-
time after the call to initscr, should be called before  exiting.
Note  however,  that  should  always be called the final calls to
which free the storage of the windows.