initscr(3ncurses)
NAME
initscr, newterm, endwin, isendwin, set_term, delscreen - curses screen initialization and manipulation routines
SYNOPSIS
#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);
DESCRIPTION
initscr 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, 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 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. 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-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. 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 · restores tty modes, · moves the cursor to the lower left-hand corner of the screen and · resets the terminal into the proper non-visual mode. Calling refresh or doupdate after a temporary escape causes the program to resume visual mode. isendwin The isendwin routine returns TRUE if endwin has been called without any subsequent calls to wrefresh, and FALSE otherwise. set_term 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. 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.
RETURN VALUE
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.
NOTES
Note that initscr and newterm may be macros.
PORTABILITY
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, 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.
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 setupterm
(see curs_terminfo(3X)) and cannot be used for full-screen operation.
Other implementations may handle a missing/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 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 initially 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.
SEE ALSO
ncurses(3NCURSES), kernel(3NCURSES), refresh(3NCURSES), slk(3NCURSES), terminfo(3NCURSES), util(3NCURSES), curses_variables(3NCURSES). initscr(3NCURSES)
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