curs_initscr(3x) Library calls curs_initscr(3x)
initscr, newterm, endwin, isendwin, set_term, delscreen - curses screen
initialization and manipulation routines
#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);
initscr 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 curs-
es 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 re-
turned 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 re-
turns a variable of type SCREEN * which should be saved as a reference
to that terminal. newterm's arguments are
o the type of the terminal to be used in place of $TERM,
o an output stream connected to the terminal, and
o an input stream connected to the terminal
If the type parameter is NULL, $TERM will be used.
The file descriptor of the output stream is passed to setupterm(3x),
which returns a pointer to a TERMINAL structure. newterm's return val-
ue holds a pointer to the TERMINAL structure.
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
o resets colors to correspond with the default color pair 0,
o moves the cursor to the lower left-hand corner of the screen,
o clears the remainder of the line so that it uses the default col-
ors,
o sets the cursor to normal visibility (see curs_set(3x)),
o stops cursor-addressing mode using the exit_ca_mode terminal capa-
bility,
o 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 previ-
ous 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 com-
pletion.
Routines that return pointers always return NULL on error.
X/Open defines no error conditions. In this implementation
o endwin returns an error if the terminal was not initialized.
o 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.
o 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:
o The portable way to use initscr is once only, using refresh (see
curs_refresh(3x)) to restore the screen after endwin.
o 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:
o 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.
o However, WINDOWs are implicitly associated with a SCREEN. so that
it is reasonable to expect delscreen to deal with these.
o SVr4 curses deletes the standard WINDOW structures stdscr and
curscr as well as a work area newscr. SVr4 curses ignores other
windows.
o Since version 4.0 (1996), ncurses has maintained a list of all win-
dows for each screen, using that information to delete those win-
dows when delscreen is called.
o NetBSD copied this feature of ncurses in 2001. PDCurses follows
the SVr4 model, deleting only the standard WINDOW structures.
Different implementations may disagree regarding the level of some
functions. For example, SCREEN (returned by newterm) and TERMINAL (re-
turned by setupterm(3x)) hold file descriptors for the output stream.
If an application switches screens using set_term, or switches termi-
nals using set_curterm(3x), applications which use the output file de-
scriptor can have different behavior depending on which structure holds
the corresponding descriptor.
For example
o NetBSD's baudrate(3x) 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 curses
uses the descriptor in SCREEN.
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(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 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 ...
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 li-
brary:
SIGINT
The handler attempts to cleanup 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 On systems which have REENTRANT turned on, set_term uses func-
tions which could deadlock or misbehave in other ways.
o endwin calls other functions, many of which use stdio or other
library functions which are clearly unsafe.
SIGTERM
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).
SIGTSTP
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 curs_kernel(3x)).
SIGWINCH
This handles the window-size changes which were ignored in the
standardization efforts. The handler sets a (signal-safe) vari-
able which is later tested in wgetch (see curs_getch(3x)). If
keypad has been enabled for the corresponding window, wgetch re-
turns 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.
curses(3x), curs_kernel(3x), curs_refresh(3x), curs_slk(3x), curs_ter-
minfo(3x), curs_util(3x), curs_variables(3x).
ncurses 6.4 2023-06-10 curs_initscr(3x)