ncurses/man/curs_scanw.3x

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.\" $Id: curs_scanw.3x,v 1.62 2025/07/05 13:03:05 tom Exp $
.TH curs_scanw 3X 2025-07-05 "ncurses @NCURSES_MAJOR@.@NCURSES_MINOR@" "Library calls"
.ie \n(.g \{\
.ds `` \(lq
.ds '' \(rq
.\}
.el \{\
.ie t .ds `` ``
.el   .ds `` ""
.ie t .ds '' ''
.el   .ds '' ""
.\}
.
.de bP
.ie n  .IP \(bu 4
.el    .IP \(bu 2
..
.SH NAME
\fB\%scanw\fP,
\fB\%wscanw\fP,
\fB\%mvscanw\fP,
\fB\%mvwscanw\fP,
\fB\%vwscanw\fP,
\fB\%vw_scanw\fP \-
read formatted input from a \fIcurses\fR window
.SH SYNOPSIS
.nf
\fB#include <curses.h>
.PP
\fBint scanw(const char *\fIfmt\fP, ...);
\fBint wscanw(WINDOW *\fIwin\fP, const char *\fIfmt\fP, ...);
\fBint mvscanw(int \fIy\fP, int \fIx\fP, const char *\fIfmt\fP, ...);
\fBint mvwscanw(WINDOW *\fIwin\fP, int \fIy\fP, int \fIx\fP, const char *\fIfmt\fP, ...);
.PP
\fBint vw_scanw(WINDOW *\fIwin\fP, const char *\fIfmt\fP, va_list \fIvarglist\fP);
.PP
\fI/* obsolete */\fP
\fBint vwscanw(WINDOW *\fIwin\fP, const char *\fIfmt\fP, va_list \fIvarglist\fP);
.fi
.SH DESCRIPTION
\fB\%scanw\fP,
\fB\%wscanw\fP,
\fB\%mvscanw\fP,
and
\fB\%mvwscanw\fP
are analogous to \fI\%scanf\fP(3).
In effect,
they call \fB\%wgetstr\fP(3X) with
.I win
(or
.BR \%stdscr )
as its first argument,
then attempt conversion of the resulting string with \fI\%vsscanf\fP(3).
Fields in the string that do not map to a variable in the \fIfmt\fP
parameter are discarded.
.PP
\fB\%vwscanw\fP
and
\fB\%vw_scanw\fP are analogous to \fI\%vscanf\fP(3),
and perform a \fB\%wscanw\fP using a variable argument list.
The third argument is a \fI\%va_list\fP,
a pointer to a list of arguments,
as defined in \fI\%stdarg.h\fP.
.SH RETURN VALUE
These functions return
.B ERR
upon failure and otherwise a count of successful conversions;
this quantity may be zero.
.PP
In
.IR \%ncurses ,
failure occurs if \fI\%vsscanf\fP(3) returns
\fBEOF\fP,
or if the window pointer
.I win
is null.
.PP
Functions prefixed with \*(``mv\*('' first perform cursor movement and
fail if the position
.RI ( y ,
.IR x )
is outside the window boundaries.
.SH NOTES
No wide character counterpart functions are defined by the
\*(``wide\*(''
.I \%ncurses
configuration nor by any standard.
They are unnecessary:
to retrieve and convert a wide-character string from a
.I curses
terminal keyboard,
use these functions with the \fI\%scanf\fP(3) conversions \*(``%lc\*(''
and \*(``%ls\*('' for wide characters and strings,
respectively.
.PP
.I \%ncurses
implements \fI\%vsscanf\fP(3) internally if it is unavailable when the
library is configured.
.SH PORTABILITY
X/Open Curses Issue\ 4 describes these functions.
It specifies no error conditions for them.
.PP
.I \%ncurses
defines \fB\%vw_scanw\fP and \fB\%vwscanw\fP identically to support
legacy applications.
However,
the latter is obsolete.
.bP
X/Open Curses Issue\ 4 Version\ 2 (1996),
marked \fB\%vwscanw\fP as requiring \fI\%varargs.h\fP and
\*(``TO BE WITHDRAWN\*('',
and specified \fB\%vw_scanw\fP using the \fI\%stdarg.h\fP interface.
.bP
X/Open Curses Issue\ 5,
Draft 2 (December 2007) marked \fB\%vwscanw\fP (along with
\fB\%vwscanw\fP and the \fItermcap\fP interface) as withdrawn.
After incorporating review comments,
this became
X/Open Curses Issue\ 7 (2009).
.bP
.I \%ncurses
provides \fB\%vwscanw\fP,
but marks it as deprecated.
.PP
X/Open Curses Issues 4 and 7 both state that these functions return
\fBERR\fP or \fBOK\fP.
This is likely an erratum.
.bP
Since the underlying \fI\%scanf\fP(3) returns the number of successful
conversions,
and SVr4
.I curses
was documented to use this feature,
this may have been an editorial solecism introduced by X/Open,
rather than an intentional change.
.bP
This implementation retains compatibility with SVr4
.IR curses .
As of 2018,
NetBSD
.I curses
also returns the number of successful conversions.
Both
.I \%ncurses\fP
and NetBSD
.I curses
call \fI\%vsscanf\fP(3) to scan the string,
which returns \fBEOF\fP on error.
.bP
Portable applications should test only if the return value is \fBERR\fP,
and not compare it to \fBOK\fP,
since that value (zero) might be misleading.
.IP
One portable way to get useful results would be to use a \*(``%n\*(''
conversion at the end of the format string,
and check the value of the corresponding variable to determine how many
conversions succeeded.
.SH HISTORY
4BSD (1980)
introduced
.I \%wscanw
and its variants.
.\" https://minnie.tuhs.org/cgi-bin/utree.pl?file=4BSD/usr/src/lib/\
.\"  libcurses/scanw.c
.\" https://minnie.tuhs.org/cgi-bin/utree.pl?file=4BSD/usr/src/lib/\
.\"  libcurses/mvscanw.c
It implemented all as functions,
not macros;
this initial distribution of
.I curses
preceded the ANSI C standard of 1989,
prior to which a variadic macro facility was not widely available.
.I \%scanw
went unused in Berkeley distributions until 4.3BSD-Reno (1990),
which employed it in a game.
.\" https://minnie.tuhs.org/cgi-bin/utree.pl?file=4.3BSD-Reno/src/\
.\"  games/chess/uxdsp.c
4BSD's
.I \%wscanw
did not use
.IR \%varargs.h ","
which had been available since Seventh Edition Unix (1979).
.\" https://minnie.tuhs.org/cgi-bin/utree.pl?file=V7/usr/include/\
.\"  varargs.h
In 1991
(a couple of years after SVr4 was generally available,
and after the C standard was published),
other developers updated the library,
using
.I \%stdarg.h
internally in 4.4BSD
.IR curses .
Even with this improvement,
BSD
.I curses
did not use function prototypes
(nor even declare functions)
in
.I \%curses.h
until 1992.
.PP
4BSD documented
.I \%scanw
and
.I \%wscanw
tersely as \*(``scanf through
.IR \%stdscr "\*(''"
and \*(``scanf through
.IR win "\*('',"
respectively.
.\" https://minnie.tuhs.org/cgi-bin/utree.pl?file=4BSD/usr/man/man3/\
.\"  curses.3
SVr3 (1987)
stated
.RS
.PP
[t]hese routines correspond to \fIscanf\fP(3S),
as do their arguments and return values.
.IR \%wgetstr "()"
is called on the window,
and the resulting line is used as input for the scan.
.RE
.\" GBR can't find a source to cite for this quotation,
.\" even after checking
.\" <https://github.com/ryanwoodsmall/oldsysv/tree/master>.
.PP
SVr3 added
.IR \%vwscanw ","
describing its third parameter as a
.IR \%va_list ","
defined in
.IR \%varargs.h ","
and referred the reader to the manual pages for
.I \%varargs
and
.I \%vprintf
for detailed descriptions.
(Because SVr3 documentation does not mention
.IR \%vscanf ","
the reference to
.I \%vprintf
might not be an error).
.PP
SVr4 (1989) introduced no new variations of
.IR \%scanw ","
but provided for using either
.I \%varargs.h
or
.I \%stdarg.h
to define the
.I \%va_list
type.
.\" either header declares "va_list", but only one can be used
.PP
X/Open Curses Issue\ 4 (1995)
defined
.I \%vw_scanw
to replace
.IR \%vwscanw ","
stating that its
.I \%va_list
type is defined in
.IR \%stdarg.h "."
.SH SEE ALSO
\fB\%curses\fP(3X),
\fB\%curs_getstr\fP(3X),
\fB\%curs_printw\fP(3X),
\fB\%scanf\fP(3),
\fB\%vscanf\fP(3)