curs_initscr(3) | Library calls | curs_initscr(3)

# 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(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(3), 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(3) 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(3), 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(3)),
- stops cursor-addressing mode using the exit_ca_mode terminal capability,
- restores tty modes (see reset_shell_mode(3)).

Calling refresh(3) or doupdate(3) 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.

# 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(3)) 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(3)) hold file descriptors for the output stream. If an application switches screens using set_term, or switches terminals using set_curterm(3), applications which use the output file descriptor can have different behavior depending on which structure holds the corresponding descriptor.

For example

- NetBSD's baudrate(3) 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(3), def_prog_mode(3). 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(3) 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(3)), 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(3)).
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(3)). 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

curses(3), curs_kernel(3), curs_refresh(3), curs_slk(3), terminfo(3), curs_util(3), curs_variables(3).

2023-08-19 | ncurses 6.4