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
• 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
• 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>.
• 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.
• 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.
• 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.
• 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.
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