NetBSD/lib/libc/stdio/ungetwc.3

.\"	$NetBSD: ungetwc.3,v 1.8 2010/12/16 17:42:27 wiz Exp $
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.\"     @(#)ungetc.3	8.1 (Berkeley) 6/4/93
.\"
.Dd October 24, 2001
.Dt UNGETWC 3
.Os
.Sh NAME
.Nm ungetwc
.Nd un-get wide character from input stream
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdio.h
.In wchar.h
.Ft wint_t
.Fn ungetwc "wint_t wc" "FILE *stream"
.Sh DESCRIPTION
The
.Fn ungetwc
function pushes the wide character
.Fa wc
(converted to an wchar_t)
back onto the input stream pointed to by
.Fa stream .
The pushed-backed wide characters will be returned by subsequent reads on the
stream (in reverse order).
A successful intervening call, using the same stream, to one of the file
positioning functions
.Xr fseek 3 ,
.Xr fsetpos 3 ,
or
.Xr rewind 3
will discard the pushed back wide characters.
.Pp
One wide character of push-back is guaranteed,
but as long as there is
sufficient memory, an effectively infinite amount of pushback is allowed.
.Pp
If a character is successfully pushed-back,
the end-of-file indicator for the stream is cleared.
.Sh RETURN VALUES
The
.Fn ungetwc
function
returns
the wide character pushed-back after the conversion, or
.Dv WEOF
if the operation fails.
If the value of the argument
.Fa c
character equals
.Dv WEOF ,
the operation will fail and the stream will remain unchanged.
.Sh SEE ALSO
.Xr fseek 3 ,
.Xr getwc 3
.Sh STANDARDS
The
.Fn ungetwc
function conforms to
.St -isoC-99 .
.Sh BUGS
The current implementation uses a fixed sized ungetwc-buffer.