# curs_initscr 3x 2025-02-01 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  NULL 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.   It  returns  a
               variable  of  structure  type  SCREEN  *, 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
           cannot support a screen-oriented program, would also use  newterm.   If
           at most one terminal connection is needed, the programmer could perform
           such a capability test, decide which 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   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   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 endwin has been called without any subsequent
           calls to wrefresh(3x), 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 curses
           API function that manipulates SCREEN pointers; all others  affect  only
           the current terminal.

### 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).  Call delscreen after  endwin  when  a
           particular SCREEN structure is no longer needed.

## RETURN VALUE

           endwin returns OK on success and ERR on failure.

           In ncurses,

           o   endwin returns ERR if

               o   the terminal was not initialized,

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

               o   reset_shell_mode(3x) returns ERR.

           o   newterm  returns  ERR  if it cannot allocate storage for the SCREEN
               data structure or the top-level windows  thereof:  curscr,  newscr,
               and stdscr.

           Functions  that  return  pointers  return  NULL  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,  WINDOWs are 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.

### 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.

           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 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 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.

## 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                       2025-02-01                  curs_initscr(3x)