Ubuntu Manpage: initscr, newterm, endwin, isendwin, set_term, delscreen

Provided by: ncurses-doc_6.4+20240113-1ubuntu2_all

NAME

       initscr,  newterm, endwin, isendwin, set_term, delscreen - initialize, manipulate, or tear
       down curses terminal interface

SYNOPSIS

       #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);

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(3NCURSES),
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(3NCURSES) 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,

• an output stream connected to the terminal, and

• 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(3NCURSES), which returns a
pointer to a TERMINAL structure. newterm's return value holds a pointer to the TERMINAL
structure.

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(3NCURSES)),

• stops cursor-addressing mode using the exit_ca_mode terminal capability,

• restores tty modes (see reset_shell_mode(3NCURSES)).

Calling refresh(3NCURSES) or doupdate(3NCURSES) 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, or

           •   endwin is called more than once without updating the screen, or

           •   reset_shell_mode(3NCURSES) returns an error.

       •   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.

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(3NCURSES) 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.

High-level versus Low-level
Different implementations may disagree regarding the level of some functions. For
example, SCREEN (returned by newterm) and TERMINAL (returned by setupterm(3NCURSES)) hold
file descriptors for the output stream. If an application switches screens using
set_term, or switches terminals using set_curterm(3NCURSES), applications which use the
output file descriptor can have different behavior depending on which structure holds the
corresponding descriptor.

For example

• NetBSD's baudrate(3NCURSES) function uses the descriptor in TERMINAL. ncurses and
SVr4 use the descriptor in SCREEN.

• NetBSD and ncurses use the descriptor in TERMINAL for terminal I/O modes, e.g.,
def_shell_mode(3NCURSES), def_prog_mode(3NCURSES). SVr4 curses uses the descriptor in
SCREEN.

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(3NCURSES) 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 Issue 7, 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(3) 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 flushinp(3NCURSES), and repaints the
screen assuming that it has been completely altered. It also updates the saved
terminal modes with def_shell_mode(3NCURSES).

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(3NCURSES). 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.

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

PORTABILITY

SEE ALSO