vw_scanw(3x) — Linux manual page


curs_scanw(3X)                                                curs_scanw(3X)

NAME         top

       scanw, wscanw, mvscanw, mvwscanw, vwscanw, vw_scanw - convert format‐
       ted input from a curses window

SYNOPSIS         top

       #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         top

       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

RETURN VALUE         top

       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.

HISTORY         top

       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

       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>.

PORTABILITY         top

       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 <stdarg.h>

       ·   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

       ·   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.

SEE ALSO         top

       curses(3X), curs_getstr(3X), curs_printw(3X), curs_termcap(3X),

COLOPHON         top

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