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curs_initscr 3x 2024-02-24 ncurses 6.4 Library calls

curs_initscr(3x)                 Library calls                curs_initscr(3x)




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(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   an output stream connected to the terminal, and

       o   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(3x),
       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

       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

           o   the terminal was not initialized, or

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

           o   reset_shell_mode(3x) returns an error.

       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(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.


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(3x))  hold  file  descriptors  for  the output
       stream.  If an application switches screens using set_term, or switches
       terminals using set_curterm(3x), applications which use the output file
       descriptor can have different behavior  depending  on  which  structure
       holds the corresponding descriptor.

       For example

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

       o   NetBSD and ncurses use the descriptor in TERMINAL for terminal  I/O
           modes,  e.g.,  def_shell_mode(3x),  def_prog_mode(3x).  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(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 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 clean up 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(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(3x), and repaints the screen assuming that  it  has  been
            completely altered.  It also updates the saved terminal modes with
            def_shell_mode(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(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)



ncurses 6.4                       2024-02-24                  curs_initscr(3x)