initscr, newterm, endwin, isendwin, set_term,
delscreen - curses screen initialization and manipulation
routines
#include <ncurses/curses.h>
WINDOW *initscr(void);
int endwin(void);
bool isendwin(void);
SCREEN *newterm(const 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), 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 colors,
- sets the cursor to normal visibility (see curs_set(3X)),
- stops cursor-addressing mode using the exit_ca_mode terminal
capability,
- 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 completion.
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 other windows.
- 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 structures.
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 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 library:
- SIGINT
- 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.
- 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) 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.