# curs_initscr 3x 2025-08-23 ncurses 6.5 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 determines the terminal  type  and  initializes  the  library's
           SCREEN,  WINDOW,  and  other data structures.  It is normally the first
           curses function call a program performs.  However, an application  with
           unusual needs might employ a few other curses functions beforehand:

           o   slk_init(3x) to set up soft-label keys;

           o   filter(3x)  if  the  program  is  designed  to operate in a process
               pipeline;

           o   ripoffline(3x) to reserve up to five lines at the top and/or bottom
               of  the  screen  from  management  by  stdscr,  the standard curses
               window; and

           o   use_env(3x) and/or use_tioctl(3x) to configure use of  the  process
               environment  and  operating system's terminal driver, respectively,
               when determining the dimensions of the terminal display.

           Further, a curses program might call newterm prior  to  or  instead  of
           initscr in two specialized cases described in its subsection below.

           initscr  causes  the  first  refresh(3x)  call to clear the screen.  If
           errors occur, initscr writes an appropriate diagnostic message  to  the
           standard  error  stream  and  exits; otherwise, it returns a pointer to
           stdscr.

### newterm

           An application that manages multiple terminals should call newterm once
           for each such device instead of initscr.  newterm's arguments are

           o   the  type  of the associated terminal, or a null pointer to use the
               TERM environment variable;

           o   an output stream outf connected to the terminal; and

           o   an input stream inf connected to the terminal.

           newterm returns a variable of pointer-to-SCREEN type, which  should  be
           saved for later use with set_term and delscreen.

           newterm passes the file descriptor of the output stream to the terminfo
           function setupterm(3x), which returns a pointer to a TERMINAL structure
           that newterm stores in the SCREEN it returns to the application.

           An application that needs to inspect a terminal type's capabilities, so
           that it can continue to run in a line-oriented  mode  if  the  terminal
           type  does not support capabilities the application demands, would also
           use newterm.  If  at  most  one  terminal  connection  is  needed,  the
           programmer  could  perform  such  a capability test, decide the mode in
           which to operate, then  call  delscreen  on  the  pointer  returned  by
           newterm, and proceed with either initscr or a non-curses interface.

### 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 the  application  or
           temporarily suspending curses's management of the terminal.  endwin:

           o   (if   start_color(3x)   has  been  called)  resets  the  terminal's
               foreground and background colors to correspond with those of  color
               pair 0 (the default pair),

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

           o   (if  start_color(3x)  has  been  called) restores the default color
               pair,

           o   clears the line,

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

           o   if applicable, stops cursor-addressing mode using the  exit_ca_mode
               (rmcup) terminal capability, and

           o   restores terminal modes (see reset_shell_mode(3x)).

           Calling refresh(3x) or doupdate(3x) after a temporary suspension causes
           curses to resume managing the terminal.

### isendwin

           isendwin returns TRUE if wrefresh(3x) has not  been  called  since  the
           most recent endwin call, and FALSE otherwise.

### set_term

           set_term re-orients the curses library's operations to another terminal
           when the application has arranged to manage more than one with newterm.
           set_term  expects a SCREEN pointer previously returned by newterm as an
           argument, and returns the previous one.  set_term is the only  standard
           curses API function that manipulates SCREEN pointers; all others affect
           only the current terminal (but see curs_sp_funcs(3x)).

### delscreen

           delscreen  frees  the  storage  backing  the  supplied  SCREEN  pointer
           argument.   endwin does not, so that an application can resume managing
           a terminal with curses after  a  (possibly  conditional  or  temporary)
           suspension;  see  curs_kernel(3x).  Use delscreen after endwin when the
           application has no more need of a terminal device  but  will  not  soon
           exit.

## RETURN VALUE

           delscreen  returns  no  value.  endwin returns OK on success and ERR on
           failure.  isendwin returns TRUE or FALSE as described above.

           In ncurses,

           o   endwin returns ERR if

               o   the terminal was not initialized,

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

               o   its call of reset_shell_mode(3x) returns ERR; and

           o   newterm returns ERR if it cannot allocate storage  for  the  SCREEN
               structure  or  the  WINDOW structures automatically associated with
               it: curscr, newscr, and stdscr.

           Functions that return pointers  return  null  pointers  on  error.   In
           ncurses,  set_term  does not fail, and initscr exits the application if
           it does not operate successfully.

## NOTES

           ncurses establishes signal handlers when a function that initializes  a
           SCREEN,  either initscr or newterm, is first called.  Applications that
           wish to handle the following signals themselves  should  set  up  their
           corresponding handlers after initializing the screen.

           SIGINT ncurses's  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   When an application has been built with the _REENTRANT macro
                      defined (and corresponding system  support),  set_term  uses
                      functions that could deadlock or misbehave in other ways.

                  o   endwin  calls other functions, many of which use stdio(3) or
                      other library functions that are clearly unsafe.

           SIGTERM
                  ncurses uses the same handler  as  for  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
                  ncurses's  handler  manages  the terminal-generated stop signal,
                  used  in  job  control.   When  resuming  the  process,  ncurses
                  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
                  ncurses  handles  changes  to  the  terminal's  window  size,  a
                  phenomenon  ignored  in  standardization  efforts.   It  sets  a
                  (signal-safe)  variable  that  is later tested by wgetch(3x) and
                  wget_wch(3x).

                  o   wgetch returns the key code KEY_RESIZE.

                  o   wget_wch returns KEY_CODE_YES and sets its wch parameter  to
                      KEY_RESIZE.

                  At  the  same  time,  ncurses calls resizeterm(3x) to adjust the
                  standard screen stdscr and update global variables such as LINES
                  and COLS.

## PORTABILITY

           X/Open Curses Issue 4 describes these functions.  It specifies no error
           conditions for them.

### Differences

           X/Open Curses  specifies  that  portable  applications  must  not  call
           initscr more than once.

           o   The  portable  way  to  use  initscr is once only, using refresh to
               restore the screen after endwin.

           o   ncurses permits use of initscr after endwin.

           initscr in BSD, from its inception (1980)  through  the  Net/2  release
           (1991)  returned  ERR cast to a WINDOW pointer when detecting an error.
           4.4BSD (1995) instead returned a  null  pointer.   Neither  exited  the
           application.   It  is  safe  but redundant to check the return value of
           initscr in X/Open Curses.

           Calling endwin does not dispose of the memory allocated by  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, every WINDOW is implicitly associated with a SCREEN, so it
               is reasonable to expect delscreen to dispose of them.

           o   SVr4  deletes  the  standard WINDOW structures stdscr and curscr as
               well as a work area newscr.  It 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 and
               newscr.

### High-level versus Low-level Functions

           Implementations disagree regarding the level of abstraction  applicable
           to  a  function or property.  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 using the output
           file  descriptor  can  behave  differently  depending  on the structure
           holding the corresponding descriptor.

           o   NetBSD's  baudrate  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 uses  the
               descriptor in SCREEN.

       Unset TERM Environment Variable
           If  the  TERM  variable  is  not set in the environment or has an empty
           value, 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  or empty TERM variable
           differently.

### Signal Handlers

           Quoting 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...

           Section "NOTES" above discusses ncurses's signal handlers.

## HISTORY

           4BSD (1980) introduced initscr and endwin.

           SVr2 (1984) added newterm and set_term.

           SVr3.1 (1987) supplied delscreen and isendwin.

## SEE ALSO

           curses(3x),     curs_kernel(3x),     curs_refresh(3x),    curs_slk(3x),
           curs_terminfo(3x), curs_util(3x), curs_variables(3x)

    ncurses 6.5                       2025-08-23                  curs_initscr(3x)