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)