curs_scanw

Section: Miscellaneous Library Functions (3X)
Updated:
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NAME

scanw, wscanw, mvscanw, mvwscanw, vwscanw, vw_scanw - convert formatted input from a curses window

SYNOPSIS

#include <curses.h>

int scanw(const char *fmt, ...);
int wscanw(WINDOW *win, const char *fmt, ...);
int mvscanw(int y, int x, const char *fmt, ...);
int mvwscanw(WINDOW *win, int y, int x, const char *fmt, ...);
int vw_scanw(WINDOW *win, const char *fmt, va_list varglist);

/* obsolete */
int vwscanw(WINDOW *win, const char *fmt, va_list varglist);

DESCRIPTION

The scanw, wscanw and mvscanw routines are analogous to scanf [see scanf(3)]. The effect of these routines is as though wgetstr were called on the window, and the resulting line used as input for sscanf(3). Fields which do not map to a variable in the fmt field are lost.

The vwscanw and vw_scanw routines are analogous to vscanf(3). They perform a wscanw using a variable argument list. The third argument is a va_list, a pointer to a list of arguments, as defined in <stdarg.h>.

RETURN VALUE

vwscanw returns ERR on failure and an integer equal to the number of fields scanned on success.

Applications may use the return value from the scanw, wscanw, mvscanw and mvwscanw routines to determine the number of fields which were mapped in the call.

Functions with a "mv" prefix first perform a cursor movement using wmove, and return an error if the position is outside the window, or if the window pointer is null.

PORTABILITY

In this implementation, vw_scanw and vwscanw are equivalent, to support legacy applications. However, the latter (vwscanw) is obsolete:
.IP • 4 The XSI Curses standard, Issue 4 described these functions, noting that the function vwscanw is marked TO BE WITHDRAWN, and is to be replaced by a function vw_scanw using the <stdarg.h> interface.
.IP • 4 The Single Unix Specification, Version 2 states that vw_scanw is preferred to vwscanw since the latter requires including <varargs.h>, which cannot be used in the same file as <stdarg.h>. This implementation uses <stdarg.h> for both, because that header is included in <curses.h>.
.IP • 4 X/Open Curses, Issue 5 (December 2007) marked vwscanw (along with vwprintw and the termcap interface) as withdrawn.

Both XSI and The Single Unix Specification, Version 2 state that these functions return ERR or OK.
.IP • 4 Since the underlying scanf(3) can return the number of items scanned, and the SVr4 code was documented to use this feature, this is probably an editing error which was introduced in XSI, rather than being done intentionally.
.IP • 4 This implementation returns the number of items scanned, for compatibility with SVr4 curses. As of 2018, NetBSD curses also returns the number of items scanned. Both ncurses and NetBSD curses call vsscanf to scan the string, which returns EOF on error.
.IP • 4 Portable applications should only test if the return value is ERR, since the OK value (zero) is likely to be misleading.

: One possible way to get useful results would be to use a "%n" conversion at the end of the format string to ensure that something was processed.