curs_scanw(3X)

💖 curs_scanw(3X) — Library calls 💖

okay bestie, pull up a chair, we're doing formatted input today 💅 this is part of the <curses.h> cinematic universe, manual section 3X, and it's giving "scanf but make it a window".

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✨ NAME ✨

scanw, wscanw, mvscanw, mvwscanw, vwscanw, vw_scanw — read formatted input from a curses window 🫶

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🌸 SYNOPSIS 🌸

#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);

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🦋 DESCRIPTION 🦋

So scanw, wscanw, mvscanw and mvwscanw are basically scanf(3)'s cousins, fr fr. What actually happens: they call wgetstr(3X) with win (or stdscr, if you didn't hand them a window) as the first argument, and then they take that resulting string and try to convert it with vsscanf(3). And listen — any field in that string that doesn't map to a variable in the fmt parameter? Discarded. Gone. Not invited to the group chat. 🙈

vwscanw and vw_scanw are the vscanf(3) girlies — they do a wscanw but with a variable argument list. That third argument is a va_list, aka a pointer to a list of arguments, as defined in stdarg.h. iconic behavior honestly.

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👑 RETURN VALUE 👑

These functions return ERR on failure, and otherwise a count of successful conversions — and yes, that count can totally be zero, no cap.

In ncurses, failure happens if vsscanf(3) returns EOF, or if the window pointer win is null. (null window = instant L, sorry.)

Functions with the mv prefix first do a cursor movement, and they fail if the position (y, x) is outside the window boundaries. stay in your lane, literally 🚧

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🌈 NOTES 🌈

Not a single wide character counterpart function is defined by the "wide" ncurses configuration, and none by any standard either. And honestly? They're unnecessary 💅 — to retrieve and convert a wide-character string from a curses terminal keyboard, just use these very functions with the scanf(3) conversions "%lc" and "%ls" for wide characters and strings respectively. iykyk.

Also: ncurses implements vsscanf(3) internally if it's unavailable when the library is configured. built different, fr.

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⭐ PORTABILITY ⭐

X/Open Curses Issue 4 describes these functions. It specifies no error conditions for them. (bold of it.)

ncurses defines vw_scanw and vwscanw identically, to support legacy applications. However, the latter is obsolete 🪦.

• 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.
• 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).
• ncurses 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 👀

• 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.
• 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.
• 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. (yes bestie, this is the trick, take notes 📝)

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💀 HISTORY 💀

4BSD (1980) introduced wscanw and its variants. It implemented all of them as functions, not macros — this initial distribution of curses preceded the ANSI C standard of 1989, and before that, a variadic macro facility was not widely available. scanw went unused in Berkeley distributions until 4.3BSD-Reno (1990), which employed it in a game 🎮. 4BSD's wscanw did not use varargs.h, which 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. the way that took a whole decade 😭

4BSD documented scanw and wscanw tersely as "scanf through stdscr" and "scanf through win", respectively. SVr3 (1987) stated

[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 added 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 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.

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🎀 SEE ALSO 🎀

curses(3X), curs_getstr(3X), curs_printw(3X), scanf(3), vscanf(3)

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and that's the whole page bestie, you ate it up 💅✨ this was ncurses 6.6, dated 2025-07-05, manual page curs_scanw(3X) — go forth and scan some formatted input, main character 🌸🦋💖