- 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 result-
- ing line used as input for sscanf(3). Fields which do not
- map to a variable in the fmt field are lost.
+ scanw, wscanw, mvscanw, and mvwscanw are analogous to scanf(3). In
+ effect, they call wgetstr(3x) with win (or stdscr) as its first
+ argument, 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.
- The vwscanw and vw_scanw routines are analogous to
- vscanf(3). They perform a wscanw using a variable argu-
- ment list. The third argument is a va_list, a pointer to
- a list of arguments, as defined in <stdarg.h>.
+ 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.
- vwscanw returns ERR on failure and an integer equal to the
- number of fields scanned on success.
+ These functions return ERR upon failure and otherwise a count of
+ successful conversions; this quantity may be zero.
+
+ In ncurses, failure occurs if vsscanf(3) returns EOF, or if the window
+ pointer win is null.
+
+ Functions with a "mv" prefix first perform a cursor movement using
+ wmove, and fail if the position is outside the window.
+
- 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.
+
+ No wide character counterpart functions are defined by the "wide"
+ ncurses configuration nor by any standard. They are unnecessary: to
+ retrieve and convert a wide-character string from a curses terminal
+ keyboard, use these functions with the scanf(3) conversions "%lc" and
+ "%ls" for wide characters and strings, respectively.
- Functions with a "mv" prefix first perform a cursor move-
- ment using wmove, and return an error if the position is
- outside the window, or if the window pointer is null.
+ ncurses implements vsscanf(3) internally if it is unavailable when the
+ library is configured.
- The XSI Curses standard, Issue 4 describes these func-
- tions. The function vwscanw is marked TO BE WITHDRAWN,
- and is to be replaced by a function vw_scanw using the
- <stdarg.h> interface. The Single Unix Specification, Ver-
- sion 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>.
-
- 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 fea-
- ture, this is probably an editing error which was intro-
- duced in XSI, rather than being done intentionally. Por-
- table 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.
+ 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
+ applications. However, the latter is obsolete.
+
+ o 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.
+
+ o X/Open Curses, Issue 5, Draft 2 (December 2007) marked vwscanw
+ (along with vwscanw and the termcap interface) as withdrawn. After
+ incorporating review comments, this became X/Open Curses, Issue 7
+ (2009).
+
+ oncurses 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.
+
+ o Since the underlying scanf(3) returns the number of successful
+ conversions, 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.
+
+ o This implementation retains compatibility with SVr4 curses. As of
+ 2018, NetBSD curses also returns the number of successful
+ conversions. Both ncurses and NetBSD curses call vsscanf(3) to
+ scan the string, which returns EOF on error.
+
+ o Portable applications should test only if the return value is ERR,
+ and not compare it to OK, since that value (zero) might be
+ misleading.
+
+ 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.
+
+
+
+ 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 internally 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
+ using either varargs.h or stdarg.h to define the va_list type.
+
+ X/Open Curses, Issue 4 (1995), defined vw_scanw to replace vwscanw,
+ stating that its va_list type is defined in stdarg.h.