initscr, newterm, endwin, isendwin, set_term, delscreen - curses screen
   initialization and manipulation routines


   #include <curses.h>

   WINDOW *initscr(void);
   int endwin(void);
   bool isendwin(void);
   SCREEN *newterm(char *type, FILE *outfd, FILE *infd);
   SCREEN *set_term(SCREEN *new);
   void delscreen(SCREEN* sp);


   initscr is normally the first curses routine to call when  initializing
   a  program.   A few special routines sometimes need to be called before
   it; these are slk_init, filter,  ripoffline,  use_env.   For  multiple-
   terminal applications, newterm may be called before initscr.

   The  initscr  code  determines  the  terminal  type and initializes all
   curses data structures.  initscr also causes the first call to  refresh
   to  clear  the  screen.  If errors occur, initscr writes an appropriate
   error message to standard error and  exits;  otherwise,  a  pointer  is
   returned to stdscr.

   A program that outputs to more than one terminal should use the newterm
   routine for each terminal instead of initscr.  A program that needs  to
   inspect capabilities, so it can continue to run in a line-oriented mode
   if the terminal cannot support a screen-oriented  program,  would  also
   use  newterm.   The  routine  newterm  should  be  called once for each
   terminal.  It returns a variable of type SCREEN * which should be saved
   as a reference to that terminal.  newterm's arguments are

   ·   the type of the terminal to be used in place of $TERM,

   ·   a file pointer for output to the terminal, and

   ·   another file pointer for input from the terminal

   If the type parameter is NULL, $TERM will be used.

   The  program  must also call endwin for each terminal being used before
   exiting from curses.  If newterm is called more than once for the  same
   terminal, the first terminal referred to must be the last one for which
   endwin is called.

   A program should always call endwin before  exiting  or  escaping  from
   curses mode temporarily.  This routine

   ·   restores tty modes,

   ·   moves the cursor to the lower left-hand corner of the screen and

   ·   resets the terminal into the proper non-visual mode.

   Calling refresh or doupdate after a temporary escape causes the program
   to resume visual mode.

   The isendwin routine returns TRUE if endwin has been called without any
   subsequent calls to wrefresh, and FALSE otherwise.

   The  set_term  routine  is  used to switch between different terminals.
   The screen  reference  new  becomes  the  new  current  terminal.   The
   previous terminal is returned by the routine.  This is the only routine
   which manipulates SCREEN pointers; all other routines affect  only  the
   current terminal.

   The  delscreen  routine  frees  storage associated with the SCREEN data
   structure.  The endwin routine does not do this, so delscreen should be
   called after endwin if a particular SCREEN is no longer needed.


   endwin  returns  the  integer  ERR  upon failure and OK upon successful

   Routines that return pointers always return NULL on error.

   X/Open defines no error conditions.  In this implementation

   ·   endwin returns an error if the terminal was not initialized.

   ·   newterm returns an error if it cannot allocate the data  structures
       for  the  screen,  or  for the top-level windows within the screen,
       i.e., curscr, newscr, or stdscr.

   ·   set_term returns no error.


   Note that initscr and newterm may be macros.


   These functions were described in the XSI Curses standard, Issue 4.  As
   of 2015, the current document is X/Open Curses, Issue 7.

   X/Open  specifies that portable applications must not call initscr more
   than once:

   ·   The portable way to use initscr is once only,  using  refresh  (see
       curs_refresh(3X)) to restore the screen after endwin.

   ·   This implementation allows using initscr after endwin.

   Old versions of curses, e.g., BSD 4.4, may have returned a null pointer
   from initscr when an error is detected, rather  than  exiting.   It  is
   safe but redundant to check the return value of initscr in XSI Curses.

   Unset TERM Variable
   If  the  TERM  variable  is  missing  or  empty, initscr uses the value
   “unknown”, which normally corresponds to  a  terminal  entry  with  the
   generic  (gn)  capability.   Generic  entries are detected by setupterm
   (see curs_terminfo(3X)) and cannot be used for  full-screen  operation.
   Other   implementations   may  handle  a  missing/empty  TERM  variable

   Signal Handlers
   Quoting from X/Open Curses, section 3.1.1:

        Curses implementations may provide for  special  handling  of  the
        SIGINT,  SIGQUIT  and  SIGTSTP  signals  if  their  disposition is
        SIG_DFL at the time initscr() is called ...

        Any special handling for these signals may remain  in  effect  for
        the  life  of  the  process  or  until  the  process  changes  the
        disposition of the signal.

        None of the Curses functions are required to be safe with  respect
        to signals ...

   This  implementation establishes signal handlers during initialization,
   e.g., initscr or newterm.  Applications which must handle these signals
   should  set  up  the  corresponding  handlers  after  initializing  the

        The handler attempts to cleanup the screen on exit.   Although  it
        usually works as expected, there are limitations:

        ·   Walking  the  SCREEN list is unsafe, since all list management
            is done without any signal blocking.

        ·   On systems which  have  REENTRANT  turned  on,  set_term  uses
            functions which could deadlock or misbehave in other ways.

        ·   endwin calls other functions, many of which use stdio or other
            library functions which are clearly unsafe.

        This uses the same handler as SIGINT, with the  same  limitations.
        It  is  not  mentioned  in X/Open Curses, but is more suitable for
        this purpose than SIGQUIT (which is used in debugging).

        This handles the stop signal, used in job control.  When  resuming
        the  process,  this  implementation  discards  pending  input with
        flushinput (see curs_util(3X)), and repaints the  screen  assuming
        that  it  has  been completely altered.  It also updates the saved
        terminal modes with def_shell_mode (see curs_kernel(3X)).

        This handles the window-size changes which were initially  ignored
        in  the standardization efforts.  The handler sets a (signal-safe)
        variable which is later tested in wgetch (see curs_getch(3X)).  If
        keypad  has  been  enabled  for  the  corresponding window, wgetch
        returns the key symbol KEY_RESIZE.  At the same time, wgetch calls
        resizeterm  to adjust the standard screen stdscr, and update other
        data such as LINES and COLS.


   ncurses(3NCURSES), kernel(3NCURSES), refresh(3NCURSES),  slk(3NCURSES),
   terminfo(3NCURSES), util(3NCURSES), curses_variables(3NCURSES).



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