curs_scanw(3x) curs_scanw(3x)
scanw, wscanw, mvscanw, mvwscanw, vwscanw, vw_scanw - convert formatted
input from a curses window
#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);
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>.
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.
While scanw was implemented in 4BSD, none of the BSD releases used it
until 4.4BSD (in a game). That early version of curses was before the
ANSI C standard. It did not use <varargs.h>, though that was
available. 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> internally in 4.4BSD curses.
Even with this improvement, BSD curses did not use function prototypes
(or even declare functions) in the <curses.h> header until 1992.
SVr2 documented scanw, wscanw tersely as "scanf through stdscr" and
tersely as "scanf through win", respectively.
SVr3 added mvscanw, and mvwscanw, with a three-line summary saying that
they were analogous to scanf(3), explaining that the string which would
be output from scanf(3) would instead be output using waddstr on the
given window. SVr3 also added vwscanw, saying that the third parameter
is a va_list, defined in <varargs.h>, and referring the reader to the
manual pages for varargs and vprintf for detailed descriptions.
(Because the SVr3 documentation does not mention vscanf, that reference
to vprintf may not be an error).
SVr4 added no new variations of scanw, but provided for using
<varargs.h> or <stdarg.h> to define the va_list type.
X/Open Curses added vw_scanw to replace vwscanw, stating that its
va_list definition requires <stdarg.h>.
In this implementation, vw_scanw and vwscanw are equivalent, to support
legacy applications. However, the latter (vwscanw) is obsolete:
o 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.
o 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>.
o 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.
o 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.
o 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.
o 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.
curses(3x), curs_getstr(3x), curs_printw(3x), curs_termcap(3x),
scanf(3).
curs_scanw(3x)