initscr(3NCURSES) Library calls initscr(3NCURSES)
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, re-
spectively, 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 std-
scr.
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 NULL to use the TERM envi-
ronment variable;
• an output stream outf connected to the terminal; and
• an input stream inf connected to the terminal. It returns a vari-
able 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(3NCURSES), which returns a pointer to a TERMINAL
structure that newterm stores in the SCREEN it returns to the applica-
tion.
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 can-
not 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:
• 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 colors,
• 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 sus-
pension causes curses to resume managing the terminal.
isendwin
isendwin returns TRUE if endwin has been called without any subsequent
calls to wrefresh(3NCURSES), 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 argu-
ment. endwin does not, so that an application can resume managing a
terminal with curses after a (possibly conditional or temporary) suspen-
sion; see kernel(3NCURSES). Call delscreen after endwin when a particu-
lar SCREEN structure is no longer needed.
RETURN VALUE
endwin returns OK on success and ERR on failure.
In ncurses,
• endwin returns ERR if
• the terminal was not initialized,
• endwin is called more than once without updating the screen, or
• reset_shell_mode(3NCURSES) returns ERR.
• 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 cor-
responding handlers after initializing the screen.
SIGINT ncurses's handler attempts to clean up the screen on exit. Al-
though 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 limi-
tations. It is not mentioned in X/Open Curses, but is more suit-
able 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 phenome-
non 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 re-
store 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 ap-
plication. 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 docu-
mentation 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 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 win-
dows 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.
High-level versus Low-level
Different implementations may disagree regarding the level of some func-
tions. 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 which use the output file de-
scriptor can have different behavior depending on which structure holds
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 Variable
If the TERM variable is missing or empty, initscr uses the value “un-
known”, 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/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
ncurses(3NCURSES), kernel(3NCURSES), refresh(3NCURSES), slk(3NCURSES),
terminfo(3NCURSES), util(3NCURSES), curses_variables(3NCURSES)
ncurses 6.5 2025-02-01 initscr(3NCURSES)
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