curs_initscr(3x) 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(char *type, FILE *outfd, FILE *infd);
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), fil-
ter, ripoffline, use_env. For multiple-terminal applica-
tions, newterm may be called before initscr.
The initscr code determines the terminal type and initial-
izes 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 ter-
minal 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
o the type of the terminal to be used in place of $TERM,
o a file pointer for output to the terminal, and
o 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 es-
caping from curses mode temporarily. This routine
o restores tty modes,
o moves the cursor to the lower left-hand corner of the
screen and
o resets the terminal into the proper non-visual mode.
Calling refresh(3x) or doupdate 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 cur-
rent terminal. The previous terminal is returned by the
routine. This is the only routine which manipulates
SCREEN pointers; all other routines affect only the cur-
rent 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 par-
ticular SCREEN is no longer needed.
endwin returns the integer ERR upon failure and OK upon
successful completion.
Routines that return pointers always return NULL on error.
X/Open defines no error conditions. In this implementa-
tion
o endwin returns an error if the terminal was not ini-
tialized.
o newterm returns an error if it cannot allocate the da-
ta 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.
Note that initscr and newterm may be macros.
These functions were described in the XSI Curses standard,
Issue 4. As of 2015, the current document is X/Open Curs-
es, 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, 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 Curses.
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 can-
not be used for full-screen operation. Other implementa-
tions may handle a missing/empty TERM variable different-
ly.
Quoting from X/Open Curses, section 3.1.1:
Curses implementations may provide for special han-
dling 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 corre-
sponding handlers after initializing the library:
SIGINT
The handler attempts to cleanup the screen on exit.
Although it usually works as expected, there are lim-
itations:
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 functions which could deadlock or
misbehave in other ways.
o endwin calls other functions, many of which use
stdio or other library functions which are clear-
ly 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 dis-
cards 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 ini-
tially 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 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_terminfo(3x), curs_util(3x), curs_vari-
ables(3x).
curs_initscr(3x)