curs_initscr(3x) — Linux manual page


curs_initscr(3X)                                        curs_initscr(3X)

NAME         top

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

SYNOPSIS         top

       #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         top

       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.

       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

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

       •   stops cursor-addressing mode using the exit_ca_mode terminal

       •   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.

RETURN VALUE         top

       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.

PORTABILITY         top

       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, 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

   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

            •   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

            •   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 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         top

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

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