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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | PORTABILITY | SEE ALSO | COLOPHON |
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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(const char *type, FILE *outfd, FILE *infd);
SCREEN *set_term(SCREEN *new);
void delscreen(SCREEN* sp);
initscr
initscr is normally the first curses routine to call when ini‐
tializing 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; other‐
wise, a pointer is returned to stdscr.
newterm
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-ori‐
ented 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.
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 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.
isendwin
The isendwin routine returns TRUE if endwin has been called with‐
out any subsequent calls to wrefresh, and FALSE otherwise.
set_term
The set_term routine is used to switch between different termi‐
nals. 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 rou‐
tines affect only the current terminal.
delscreen
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 success‐
ful 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 with‐
in 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.
Differences
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 point‐
er 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 fol‐
lows the SVr4 model, deleting only the standard WINDOW struc‐
tures.
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 se‐
tupterm (see curs_terminfo(3X)) and cannot be used for full-
screen operation. Other implementations may handle a miss‐
ing/empty TERM variable differently.
Signal Handlers
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 initial‐
ization, e.g., initscr or newterm. Applications which must han‐
dle these signals should set up the corresponding handlers after
initializing the library:
SIGINT
The handler attempts to cleanup the screen on exit. Al‐
though it usually works as expected, there are limitations:
• Walking the SCREEN list is unsafe, since all list man‐
agement 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 limita‐
tions. It is not mentioned in X/Open Curses, but is more
suitable for this purpose than SIGQUIT (which is used in de‐
bugging).
SIGTSTP
This handles the stop signal, used in job control. When re‐
suming the process, this implementation discards pending in‐
put with flushinput (see curs_util(3X)), and repaints the
screen assuming that it has been completely altered. It al‐
so 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 corre‐
sponding 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.
curses(3X), curs_kernel(3X), curs_refresh(3X), curs_slk(3X),
curs_terminfo(3X), curs_util(3X), curs_variables(3X).
This page is part of the ncurses (new curses) project. Informa‐
tion about the project can be found at
⟨https://www.gnu.org/software/ncurses/ncurses.html⟩. If you have
a bug report for this manual page, send it to
bug-ncurses-request@gnu.org. This page was obtained from the
project's upstream Git mirror of the CVS repository
⟨https://github.com/mirror/ncurses.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2023-03-12.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
curs_initscr(3X)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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