initscrinitscr 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
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.
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
· the type of the terminal to be used in place of $TERM,
· a file pointer for output to the terminal, and
· another file pointer for input from the terminal
If the type parameter is NULL, $TERM will be used.
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
· resets colors to correspond with the default color pair 0,
· moves the cursor to the lower left-hand corner of the screen,
· clears the remainder of the line so that it uses the default
· sets the cursor to normal visibility (see curs_set(3X)),
· stops cursor-addressing mode using the exit_ca_mode terminal
· 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.
The isendwin routine returns TRUE if endwin has been called without
any subsequent calls to wrefresh, and FALSE otherwise.
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.
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.
endwin returns the integer ERR upon failure and OK upon successful
Routines that return pointers always return NULL on error.
X/Open defines no error conditions. In this implementation
· endwin returns an error if the terminal was not initialized.
· 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.
· set_term returns no error.
These functions were described in the XSI Curses standard, Issue 4.
As of 2015, the current document is X/Open Curses, Issue 7.
X/Open specifies that portable applications must not call initscr
more than once:
· The portable way to use initscr is once only, using refresh (see
curs_refresh(3X)) to restore the screen after endwin.
· This implementation allows using initscr after endwin.
Old versions of curses, e.g., BSD 4.4, may have returned 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
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
(see curs_terminfo(3X)) and cannot be used for full-screen operation.
Other implementations may handle a missing/empty TERM variable
Quoting from X/Open Curses, section 3.1.1:
Curses implementations may provide for special handling of theSIGINT, SIGQUIT and SIGTSTP signals if their disposition isSIG_DFL at the timeinitscr is called...Any special handling for these signals may remain in effect forthe life of the process or until the process changes thedisposition of the signal.None of the Curses functions are required to be safe withrespect 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:
The handler attempts to cleanup 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.
· On systems which have REENTRANT turned on, set_term uses
functions which could deadlock or misbehave in other ways.
· endwin calls other functions, many of which use stdio or
other library functions which are clearly unsafe.
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).
This handles the stop signal, used in job control. When
resuming the process, this implementation discards pending input
with flushinput (see curs_util(3X)), and repaints the screen
assuming that it has been completely altered. It also updates
the saved terminal modes with def_shell_mode (see
This handles the window-size changes which were initially
ignored in the standardization efforts. The handler sets a
(signal-safe) variable which is later tested in wgetch (see
curs_getch(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.
This page is part of the ncurses (new curses) project. Information
about the project can be found at
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