scanw(3NCURSES) Library calls scanw(3NCURSES)
NAME
scanw, wscanw, mvscanw, mvwscanw, vwscanw, vw_scanw - read formatted in-
put 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
scanw, wscanw, mvscanw, and mvwscanw are analogous to scanf(3). In ef-
fect, they call wgetstr(3NCURSES) with win (or stdscr) as its first ar-
gument, then attempt conversion of the resulting string with vsscanf(3).
Fields in the string that do not map to a variable in the fmt parameter
are discarded.
vwscanw and vw_scanw are analogous to vscanf(3), and 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
These functions return ERR upon failure and otherwise a count of suc-
cessful conversions; this quantity may be zero.
In ncurses, failure occurs if vsscanf(3) returns EOF, or if the window
pointer win is null.
Functions prefixed with “mv” first perform cursor movement and fail if
the position (y, x) is outside the window boundaries.
NOTES
No wide character counterpart functions are defined by the “wide”
ncurses configuration nor by any standard. They are unnecessary: to re-
trieve and convert a wide-character string from a curses terminal key-
board, use these functions with the scanf(3) conversions “%lc” and “%ls”
for wide characters and strings, respectively.
ncurses implements vsscanf(3) internally if it is unavailable when the
library is configured.
PORTABILITY
X/Open Curses Issue 4 describes these functions. It specifies no error
conditions for them.
ncurses defines vw_scanw and vwscanw identically to support legacy ap-
plications. However, the latter is obsolete.
• X/Open Curses Issue 4 Version 2 (1996), marked vwscanw as requiring
varargs.h and “TO BE WITHDRAWN”, and specified vw_scanw using the
stdarg.h interface.
• X/Open Curses Issue 5, Draft 2 (December 2007) marked vwscanw (along
with vwscanw and the termcap interface) as withdrawn. After incor-
porating review comments, this became X/Open Curses Issue 7 (2009).
• ncurses provides vwscanw, but marks it as deprecated.
X/Open Curses Issues 4 and 7 both state that these functions return ERR
or OK. This is likely an erratum.
• Since the underlying scanf(3) returns the number of successful con-
versions, and SVr4 curses was documented to use this feature, this
may have been an editorial solecism introduced by X/Open, rather
than an intentional change.
• This implementation retains compatibility with SVr4 curses. As of
2018, NetBSD curses also returns the number of successful conver-
sions. Both ncurses and NetBSD curses call vsscanf(3) to scan the
string, which returns EOF on error.
• Portable applications should test only if the return value is ERR,
and not compare it to OK, since that value (zero) might be mislead-
ing.
One portable way to get useful results would be to use a “%n” con-
version at the end of the format string, and check the value of the
corresponding variable to determine how many conversions succeeded.
HISTORY
scanw was implemented in 4BSD (November 1980); that early version of
curses preceded the ANSI C standard of 1989. The function was unused in
Berkeley distributions for over ten years, until 4.4BSD, which employed
it in a game. The 4BSD scanw did not use varargs.h, though that had
been available since Seventh Edition Unix (1979). In 1991 (a couple of
years after SVr4 was generally available, and after the C standard was
published), other developers updated the library, using stdarg.h inter-
nally in 4.4BSD curses. Even with this improvement, BSD curses did not
use function prototypes (nor even declare functions) in curses.h until
1992.
SVr2 (1984) documented scanw and wscanw tersely as “scanf through
stdscr” and “scanf through win”, respectively.
SVr3 (1987) added mvscanw, and mvwscanw, stating
“[t]hese routines correspond to scanf(3S), as do their arguments
and return values. wgetstr() is called on the window, and the
resulting line is used as input for the scan.”
SVr3 also implemented vwscanw, describing its third parameter as a
va_list, defined in varargs.h, and referred the reader to the manual
pages for varargs and vprintf for detailed descriptions. (Because the
SVr3 documentation does not mention vscanf, the reference to vprintf
might not be an error).
SVr4 (1989) introduced no new variations of scanw, but provided for us-
ing either varargs.h or stdarg.h to define the va_list type.
X/Open Curses Issue 4 (1995), defined vw_scanw to replace vwscanw, stat-
ing that its va_list type is defined in stdarg.h.
SEE ALSO
ncurses(3NCURSES), getstr(3NCURSES), printw(3NCURSES), scanf(3),
vscanf(3)
ncurses 6.5 2025-01-18 scanw(3NCURSES)
Generated by dwww version 1.16 on Sat Oct 3 05:20:22 CEST 2026.