# curs_initscr 3x

    curs_initscr(3x)                                              curs_initscr(3x)

## 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 curs-
           es 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  re-
           turned 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 termi-
           nal.  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 col-
               ors,

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

           o   stops cursor-addressing mode using the exit_ca_mode terminal  capa-
               bility,

           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  previ-
           ous  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 com-
           pletion.

           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 docu-
               mentation 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 win-
               dows  for  each screen, using that information to delete those win-
               dows 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 "un-
           known", 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  li-
           brary:

           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 func-
                    tions 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)  vari-
                able  which  is  later  tested in wgetch (see curs_getch(3x)).  If
                keypad has been enabled for the corresponding window,  wgetch  re-
                turns  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_ter-
           minfo(3x), curs_util(3x), curs_variables(3x).

                                                                  curs_initscr(3x)