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curs_initscr(3)                                                curs_initscr(3)




NAME

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


SYNOPSIS

       #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);


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(3X), 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(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.

   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

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

       o   a file pointer for output to the terminal, and

       o   another file pointer for input from the terminal

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

   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

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

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

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

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

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

       o   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.

   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

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

       o   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.

       o   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:

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

       o   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:

       o   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.

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

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

       o   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.

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

   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:

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

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

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

            o   endwin calls other functions, many of which use stdio 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
            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)).

       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 (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.


SEE ALSO

       curses(3X), curs_kernel(3X), curs_refresh(3X), curs_slk(3X),
       curs_terminfo(3X), curs_util(3X), curs_variables(3X).



                                                                curs_initscr(3)

ncurses 6.4 - Generated Wed Jan 4 18:45:27 CST 2023
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