Ubuntu Manpage: initscr, newterm, endwin, isendwin, set_term, delscreen - initialize, manipulate, or tear down curses

Provided by: ncurses-doc_6.5+20251123-1_all

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:

       •   slk_init(3NCURSES) to set up soft-label keys;

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

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

       •   use_env(3NCURSES)  and/or  use_tioctl(3NCURSES)  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(3NCURSES) 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

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

       •   an output stream outf connected to the terminal; and

       •   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(3NCURSES),
       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:

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

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

       •   (if start_color(3NCURSES) has been called) restores the default color pair,

       •   clears the line,

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

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

       •   restores terminal modes (see reset_shell_mode(3NCURSES)).

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

   isendwin
       isendwin returns TRUE if wrefresh(3NCURSES) 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 sp_funcs(3NCURSES)).

   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 kernel(3NCURSES).  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,

       •   endwin returns ERR if

           •   the terminal was not initialized,

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

           •   its call of reset_shell_mode(3NCURSES) returns ERR; and

       •   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.

• Walking the SCREEN list is unsafe, since all list management is done without any signal
blocking.

• 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.

• 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(3NCURSES) and repaints the screen,
assuming that it has been completely altered. It also updates the saved terminal modes with
def_shell_mode(3NCURSES).

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(3NCURSES) and
wget_wch(3NCURSES).

• wgetch returns the key code KEY_RESIZE.

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

At the same time, ncurses calls resizeterm(3NCURSES) 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.

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

• 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.

• 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, every WINDOW is implicitly associated with a SCREEN, so it is reasonable to expect delscreen
to dispose of them.

• SVr4 deletes the standard WINDOW structures stdscr and curscr as well as a work area newscr. It
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 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(3NCURSES)) hold file
descriptors for the output stream. If an application switches screens using set_term, or switches
terminals using set_curterm(3NCURSES), applications using the output file descriptor can behave
differently depending on the structure holding the corresponding descriptor.

• NetBSD's baudrate function uses the descriptor in TERMINAL. ncurses and SVr4 use the descriptor in
SCREEN.

• NetBSD and ncurses use the descriptor in TERMINAL for terminal I/O modes, e.g.,
def_shell_mode(3NCURSES), def_prog_mode(3NCURSES). 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(3NCURSES) 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.