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 before initscr.
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 arguments are
• 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
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, would return 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 Curses.
Calling endwin does not dispose of the memory allocated in
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, WINDOWs are implicitly associated with a SCREEN. so
that it is reasonable to expect delscreen to deal with these.
• SVr4 curses deletes the standard WINDOW structures stdscr and
curscr as well as a work area newscr. SVr4 curses ignores
• 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
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 differently.
Quoting from X/Open Curses, section 3.1.1:
Curses implementations may provide for special handling oftheSIGINT,SIGQUIT andSIGTSTP signals if their dispositionisSIG_DFL at the timeinitscr is called ...
Any special handling for these signals may remain in effectfor the 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
• 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
• 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
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
This handles the window-size changes which were 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.
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