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       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(const 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(3X), filter,
       ripoffline, use_env.  For multiple-terminal applications, newterm  may  be  called  before

       The  initscr code determines the terminal type and initializes all curses data structures.
       initscr also causes the first call to refresh(3X) 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

       ·   resets colors to correspond with the default color pair 0,

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

       ·   clears the remainder of the line so that it uses the default colors,

       ·   sets the cursor to normal visibility (see curs_set(3X)),

       ·   stops cursor-addressing mode using the exit_ca_mode terminal capability,

       ·   restores tty modes (see reset_shell_mode(3X)).

       Calling refresh(3X) or doupdate(3X) 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 completion.

       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.


       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 differently.

   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 library:

            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 kernel(3NCURSES)).

            This handles the window-size  changes  which  were  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).