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 6.6 2025-08-23 curs_initscr(3X)