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curs_get_wstr

Section: Library calls (3X)
Updated: 202-1-20
Index Return to Main Contents

NAME

get_wstr, getn_wstr, wget_wstr, wgetn_wstr, mvget_wstr, mvgetn_wstr, mvwget_wstr, mvwgetn_wstr - read a wid-character string from a curses terminal keyboard

SYNOPSIS

#include <curses.h>

int get_wstr(wint_t * wstr);
int wget_wstr(WINDOW * win, wint_t * wstr);
int mvget_wstr(int y, int x, wint_t * wstr);
int mvwget_wstr(WINDOW * win, int y, int x, wint_t * wstr);

int getn_wstr(wint_t * wstr, int n);
int wgetn_wstr(WINDOW * win, wint_t * wstr, int n);
int mvgetn_wstr(int y, int x, wint_t * wstr, int n);
int mvwgetn_wstr(WINDOW * win, int y, int x, wint_t * wstr, int n);

DESCRIPTION

wget_wstr populates a use-supplied wid-character string buffer wstr by repeatedly calling wget_wch(3X) with the win argument until a line feed or carriage return character is input. The function
.IP * 4 does not copy the terminating character to wstr;
.IP * 4 populates wstr with WEOF (as defined in wchar.h) if an en-o-file condition occurs on the input;
.IP * 4 always terminates the string with a null wide character (after any WEOF);
.IP * 4 interprets the screen's wide erase and wide kill characters (see erasewchar(3X) and killwchar(3X));
.IP * 4 recognizes function keys only if the screen's keypad option is enabled (see keypad(3X));
.IP * 4 treats the function keys KEY_LEFT and KEY_BACKSPACE the same as the wide erase character; and
.IP * 4 discards function key inputs other than those treated as the wide erase or wide kill characters, calling beep(3X).

The wide erase character replaces the character at the end of the buffer with a null wide character, while the wide kill character does the same for the entire buffer.

If the screen's echo option is enabled (see echo(3X)), wget_wstr updates win with wadd_wch(3X). Further,
.IP * 4 the wide erase character and its function key synonyms move the cursor to the left, and
.IP * 4 the wide kill character returns the cursor to where it was located when wget_wstr was called.

wgetn_wstr is similar, but reads at most n wide characters, aiding the application to avoid overrunning the buffer to which wstr points. curses ignores an attempt to input more than n wide characters (other than the terminating line feed or carriage return), calling beep(3X). If n is negative, wgetn_wstr reads up to LINE_MAX wide characters (see sysconf(3)).

ncurses(3X) describes the variants of these functions.

RETURN VALUE

These functions return OK on success and ERR on failure.

In ncurses, these functions fail if
.IP * 4 the curses screen has not been initialized,
.IP * 4 (for functions taking a WINDOW pointer argument) win is a null pointer,
.IP * 4 wstr is a null pointer, or
.IP * 4 an internal wget_wch(3X) call fails.

Functions prefixed with "mv" first perform cursor movement and fail if the position (y, x) is outside the window boundaries.

NOTES

All of these functions except wgetn_wstr may be implemented as macros.

Reading input that overruns the buffer pointed to by wstr causes undefined results. Use the n-infixed functions, and allocate sufficient storage for wstr - at least n+1 times sizeof(wchar_t).

These functions cannot store a KEY_ value in wstr because there is no way to distinguish it from a valid wchar_t value.

While these functions conceptually implement a series of calls to wget_wch, they also temporarily change properties of the curses screen to permit simple editing of the input buffer. Each function saves the screen's state, calls nl(3X), and, if the screen was in canonical ("cooked") mode, cbreak(3X). Before returning, it restores the saved screen state. Other implementations differ in detail, affecting which control characters they can accept in the buffer; see section "PORTABILITY" below.

Unlike getstr(3X) and related functions of ncurses's no-wide API, these functions do not return KEY_RESIZE if a SIGWINCH event interrupts the function.

EXTENSIONS

getn_wstr, wgetn_wstr, mvgetn_wstr, and mvwgetn_wstr's handing of negative n values is an ncurses extension.

PORTABILITY

Applications employing ncurses extensions should condition their use on the visibility of the NCURSES_VERSION preprocessor macro.

X/Open Curses Issue 4 describes these functions. It specifies no error conditions for them.

Issue 4 documented these functions as passing an array of wchar_t, but that was an error, conflicting with the following language in the standard.

: The effect of get_wstr() is as though a series of calls to get_wch() were made, until a newline character, en-o-line character, or en-o-file character is processed.

get_wch can return a negative value (WEOF), but wchar_t is a unsigned type. All of the vendors implement these functions using wint_t, following the Issue 7 standard.

X/Open Curses Issue 7 is unclear whether the terminating null wide character counts toward the length parameter n. A similar issue affected wgetnstr in Issue 4, Version 2; Issue 7 revised that function's description to address the issue, but not that of wget_nwstr, leaving it ambiguous. ncurses counts the terminator in the length.

X/Open Curses does not specify what happens if the length n is negative.
.IP * 4 For consistency with wgetnstr, ncurses 6.2 uses a limit based on LINE_MAX.
.IP * 4 Some other implementations (such as Solaris xcurses) do the same, while others (PDCurses) do not permit a negative n.
.IP * 4 NetBSD 7 curses imitates ncurses 6.1 and earlier, treating a negative n as an unbounded count of wide characters.

Implementations vary in their handling of input control characters.
.IP * 4 While they may enable the screen's echo option, some do not take it out of raw mode, and may take cbreak mode into account when deciding whether to handle echoing within wgetn_wstr or to rely on it as a side effect of calling wget_wch.

: Since 1995, ncurses has provided handlers for SIGINTR and SIGQUIT events, which are typically generated at the keyboard with ^C and ^ respectively. In cbreak mode, those handlers catch a signal and stop the program, whereas other implementations write those characters into the buffer.
.IP * 4 Starting with ncurses 6.3 (2021), wgetn_wstr preserves raw mode if the screen was already in that state, allowing one to enter the characters the terminal interprets as interrupt and quit events into the buffer, for consistency with SVr4 curses's wgetnstr.

HISTORY

X/Open Curses Issue 4 (1995) initially specified these functions. The System V Interface Definition Version 4 of the same year specified functions named wgetwstr and wgetnwstr (and the usual variants). These were later additions to SVr4.x, not appearing in the first SVr4 (1989). Except in name, their declarations did not differ from X/Open's later wget_wstr and wgetn_wstr until X/Open Curses Issue 7 (2009) eventually changed the type of the buffer argument to a pointer to wint_t.