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$Id: curs_kernel.3x,v 1.89 2025/08/16 19:50:07 tom Exp $
.\} .\} . .. \%def_prog_mode, \%def_shell_mode, \%reset_prog_mode, \%reset_shell_mode, \%resetty, \%savetty, \%getsyx, \%setsyx, \%curs_set, \%mvcur, \%napms, \%ripoffline - low-level curses routines

#include <curses.h>

int def_prog_mode(void);
int def_shell_mode(void);

int reset_prog_mode(void);
int reset_shell_mode(void);

int resetty(void);
int savetty(void);

void getsyx(int y, int x);
void setsyx(int y, int x);

int curs_set(int visibility);
int mvcur(int oldrow, int oldcol, int newrow, int newcol);
int napms(int ms);
int ripoffline(int line, int (*init)(WINDOW *, int));

The following routines give low-level access to various curses capabilities. These routines typically are used inside library routines. The def_prog_mode and def_shell_mode routines save the current terminal modes as the \*(``program\*('' (in curses) or \*(``shell\*('' (not in curses) state for use by the reset_prog_mode and reset_shell_mode routines. This is done automatically by initscr. There is one such save area for each screen context allocated by newterm. The reset_prog_mode and reset_shell_mode routines restore the terminal to \*(``program\*('' (in curses) or \*(``shell\*('' (out of curses) state. These are done automatically by endwin(3X) and, after an endwin, by doupdate, so they normally are not called. The resetty and savetty routines save and restore the state of the terminal modes. savetty saves the current state in a buffer and resetty restores the state to what it was at the last call to savetty. \%getsyx stores the coordinates of virtual screen \%( newscr ) cursor in y and x "." If \%newscr 's \%leaveok(3X) output option is TRUE "," \%getsyx stores -1 in both y and x "." If lines have been removed from the top of the screen using \%ripoffline "," y includes these lines; therefore, y and x populated by \%getsyx should be used only as arguments for \%setsyx "."

Few applications use this feature; most call \%getyx(3X) instead.

\%setsyx sets the virtual screen \%( newscr ) cursor location to ( y , x ")." "\%setsyx(-1, -1)" is equivalent to "\%leaveok(newscr, TRUE)" "."

\%getsyx and \%setsyx are designed to be used by a function that manipulates curses windows but seeks to avoid changing the cursor position. Such a function would first call \%getsyx "," modify its windows' content, call \%wnoutrefresh(3X) on them, call \%setsyx "," then call \%doupdate(3X).

Few applications use this feature; most call \%wmove(3X) instead.

\%curs_set adjusts the cursor visibility to \*(``invisible\*('', \*(``visible\*('', \*(``very visible\*('', as its argument is 0 , 1 , or 2 , respectively. It returns the previous visibility if the requested one is supported, and ERR otherwise. \%mvcur provides low-level cursor motion. It takes effect immediately, rather than at the next refresh. Unlike the other low-level output functions, which either write to the standard output stream or are passed a function pointer to perform output, \%mvcur uses a file descriptor derived from the output stream parameter of \%newterm(3X).

One application of \%mvcur accompanies the temporary use of another program to write to the terminal screen. For example, first call \%refresh(3X) to ensure that the screen and the library's model of it are up to date; then call \%reset_shell_mode ";" write to the screen with the external application; call \%reset_prog_mode ";" and finally call \%mvcur( ".\|.\|." , .\|.\|. , -1, -1) to move the terminal cursor to where \%curses thinks it is, since the library has no knowledge of how the external application moved it. https://lists.gnu.org/archive/html/bug-ncurses/2016-10/msg00002.html

\%napms sleeps for ms milliseconds. If ms exceeds 30,000 (thirty seconds), \%ncurses caps it at that value. \%ripoffline provides access to the same facility that \%slk_init(3X) uses to reduce the size of the screen. The application must call \%ripoffline before \%initscr(3X) or \%newterm(3X) so that the latter functions prepare a \%stdscr of the correct size. .bP If line is positive, \%ripoffline removes a line from the top of what will become \%stdscr "." .bP If line is negative, \%ripoffline removes a line from the bottom of what will become \%stdscr "."

When \%initscr initializes curses "," it calls the init function supplied to \%ripoffline by the application with two arguments: .bP a pointer to the one-line \%WINDOW that it allocates, and .bP an integer with the number of columns in the window.

Inside this init function, the values of the integer variables LINES and COLS (see \%curs_variables(3X)) are not guaranteed to be reliable; it must not call \%wrefresh(3X) or \%doupdate(3X). A \%wnoutrefresh(3X) call is permissible.

\%ripoffline can be called up to five times before \%initscr or \%newterm "."

Except for \%curs_set "," these functions return OK on success and ERR on failure.

\%curs_set returns the previous cursor visibility, and returns ERR if the terminal type does not support the requested visibility "."

\%napms always succeeds.

\%mvcur fails if the position ( newrow , newcol ) is outside the screen boundaries.

In \%ncurses "," .bP \%def_prog_mode "," \%def_shell_mode "," \%reset_prog_mode "," and \%reset_shell_mode return ERR if the terminal was not initialized, or if the operating system's function for obtaining terminal settings fails. .bP \%ripoffline returns ERR if the accumulated quantity of ripped-off lines would exceed the maximum (5).

\%getsyx is a macro; use of the & operator before its arguments is unnecessary.

The \%endwin function of both \%ncurses and SVr4 curses calls \%curs_set if the latter has previously been called to set the cursor visibility to a value other than normal; that is, either invisible or very visible. There is no way for \%ncurses to determine the initial cursor visibility to restore it.

\%ncurses imposes a limit of 30 seconds on a delay requested of \%napms .

While the init function called by \%ripoffline is specified to return an int "," \%ncurses pays no attention to its return value.

If \%ripoffline cannot allocate memory for the required \%WINDOW structure backing the ripped-off line, it stores a null pointer to the \%WINDOW pointer argument supplied by the init function the application specifies. The application must check this argument for validity after calling \%initscr and prior to performing curses operations on that window.

In \%ncurses "," \%mvcur accepts -1 for either or both old coordinates. This value tells \%ncurses that the old location is unknown, and that it must use only absolute motion, as with the \%cursor_address ( cup ) capability, rather than the least costly combination of absolute and relative motion. Applications employing \%ncurses extensions should condition their use on the visibility of the \%NCURSES_VERSION preprocessor macro.

The "virtual screen" functions \%setsyx and \%getsyx are not described in X/Open Curses Issue 4. SVr4 documents each of them as returning an int "." This is misleading, as they are macros with no documented semantics for returning values.

All other functions are as described in X/Open Curses. It specifies no error conditions for them, except as described for \%curs_set in section \*(``RETURN VALUE\*('' above.

The System V Interface Definition, Version 4 (1995), specified all of these functions except \%curs_set as returning OK "." SVID 4, vol 3., p. 518

Older SVr4 man pages warn that the return value of \%curs_set \*(``is currently incorrect\*(''. This implementation gets it right, but counting on its correctness anywhere else may be unwise.

X/Open Curses specifies \%ripoffline as returning OK with no possibility of failure (\*(``[c]alls to \%ripoffline above this limit [five lines] have no effect but report success\*('').

X/Open Curses notes:

Both \%ncurses and SVr4 curses implement \%mvcur using the SCREEN object allocated in either \%initscr(3X) or \%newterm(3X). X/Open Curses states that the old location must be given for \%mvcur to accommodate terminals that lack absolute cursor positioning. X/Open Curses Issue 7, p. 161

If interrupted by a signal, \%ncurses restarts \%napms "." That, and the limitation to 30 seconds, differ from other implementations.

\%curses(3X), \%curs_initscr(3X), \%curs_outopts(3X), \%curs_refresh(3X), \%curs_scr_dump(3X), \%curs_slk(3X), \%curs_variables(3X)