curs_scanw 3x 2023-09-16 ncurses 6.4 Library calls

curs_scanw(3x)                   Library calls                  curs_scanw(3x)


       scanw,  wscanw,  mvscanw,  mvwscanw, vwscanw, vw_scanw - read 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

       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),

ncurses 6.4                       2023-09-16                    curs_scanw(3x)