Provided by: ncurses-doc_6.4+20240113-1ubuntu2_all bug

NAME

       initscr,  newterm,  endwin,  isendwin,  set_term, delscreen - initialize, manipulate, or tear down curses
       terminal interface

SYNOPSIS

       #include <curses.h>

       WINDOW *initscr(void);
       int endwin(void);

       bool isendwin(void);

       SCREEN *newterm(const char *type, FILE *outf, FILE *inf);
       SCREEN *set_term(SCREEN *new);
       void delscreen(SCREEN* sp);

DESCRIPTION

   initscr
       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(3NCURSES), 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(3NCURSES)  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.

   newterm
       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,

       •   an output stream connected to the terminal, and

       •   an input stream connected to the terminal

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

       The  file  descriptor of the output stream is passed to setupterm(3NCURSES), which returns a pointer to a
       TERMINAL structure.  newterm's return value holds a pointer to the TERMINAL structure.

   endwin
       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(3NCURSES)),

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

       •   restores tty modes (see reset_shell_mode(3NCURSES)).

       Calling  refresh(3NCURSES)  or  doupdate(3NCURSES)  after a temporary escape causes the program to resume
       visual mode.

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

   set_term
       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.

   delscreen
       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.

RETURN VALUE

       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, or

           •   endwin is called more than once without updating the screen, or

           •   reset_shell_mode(3NCURSES) returns an error.

       •   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.

PORTABILITY

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

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

       •   The portable way to use initscr is once only, using refresh(3NCURSES) to  restore  the  screen  after
           endwin.

       •   This implementation allows using initscr after endwin.

       Old  versions  of  curses,  e.g.,  BSD  4.4,  would  return  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.

       Calling  endwin  does  not  dispose  of  the  memory  allocated in initscr or newterm.  Deleting a SCREEN
       provides a way to do this:

       •   X/Open Curses does not say what happens to WINDOWs when delscreen “frees storage associated with  the
           SCREEN”  nor  does  the  SVr4  documentation  help, adding that it should be called after endwin if a
           SCREEN is no longer needed.

       •   However, WINDOWs are implicitly associated with a  SCREEN.   so  that  it  is  reasonable  to  expect
           delscreen to deal with these.

       •   SVr4  curses  deletes the standard WINDOW structures stdscr and curscr as well as a work area newscr.
           SVr4 curses ignores other windows.

       •   Since version 4.0 (1996), ncurses has maintained a list of all windows for each  screen,  using  that
           information to delete those windows when delscreen is called.

       •   NetBSD  copied  this  feature of ncurses in 2001.  PDCurses follows the SVr4 model, deleting only the
           standard WINDOW structures.

   High-level versus Low-level
       Different implementations may disagree regarding the  level  of  some  functions.   For  example,  SCREEN
       (returned by newterm) and TERMINAL (returned by setupterm(3NCURSES)) hold file descriptors for the output
       stream.   If  an  application  switches   screens   using   set_term,   or   switches   terminals   using
       set_curterm(3NCURSES),  applications  which  use  the  output file descriptor can have different behavior
       depending on which structure holds the corresponding descriptor.

       For example

       •   NetBSD's baudrate(3NCURSES) function uses the descriptor in  TERMINAL.   ncurses  and  SVr4  use  the
           descriptor in SCREEN.

       •   NetBSD   and   ncurses   use   the   descriptor   in   TERMINAL   for   terminal   I/O  modes,  e.g.,
           def_shell_mode(3NCURSES), def_prog_mode(3NCURSES).  SVr4 curses uses the descriptor in SCREEN.

   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(3NCURSES)
       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 Issue 7, 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:

       SIGINT
            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(3) or other library  functions  which  are
                clearly unsafe.

       SIGTERM
            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).

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

       SIGWINCH
            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(3NCURSES).  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.

SEE ALSO

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