UNGETWC(3P) POSIX Programmer's Manual UNGETWC(3P)PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAMEungetwc — push wide-character code back into the input stream
SYNOPSIS
#include <stdio.h>
#include <wchar.h>
wint_t ungetwc(wint_t wc, FILE *stream);
DESCRIPTION
The functionality described on this reference page is aligned with the
ISO C standard. Any conflict between the requirements described here
and the ISO C standard is unintentional. This volume of POSIX.1‐2008
defers to the ISO C standard.
The ungetwc() function shall push the character corresponding to the
wide-character code specified by wc back onto the input stream pointed
to by stream. The pushed-back characters shall be returned by subse‐
quent reads on that stream in the reverse order of their pushing. A
successful intervening call (with the stream pointed to by stream) to a
file-positioning function (fseek(), fseeko(), fsetpos(), or rewind())
or fflush() shall discard any pushed-back characters for the stream.
The external storage corresponding to the stream is unchanged.
At least one character of push-back shall be provided. If ungetwc() is
called too many times on the same stream without an intervening read or
file-positioning operation on that stream, the operation may fail.
If the value of wc equals that of the macro WEOF, the operation shall
fail and the input stream shall be left unchanged.
A successful call to ungetwc() shall clear the end-of-file indicator
for the stream. The value of the file-position indicator for the stream
after all pushed-back characters have been read, or discarded by call‐
ing fseek(), fseeko(), fsetpos(), or rewind() (but not fflush()), shall
be the same as it was before the characters were pushed back. The file-
position indicator is decremented (by one or more) by each successful
call to ungetwc(); if its value was 0 before a call, its value is
unspecified after the call.
RETURN VALUE
Upon successful completion, ungetwc() shall return the wide-character
code corresponding to the pushed-back character. Otherwise, it shall
return WEOF.
ERRORS
The ungetwc() function may fail if:
EILSEQ An invalid character sequence is detected, or a wide-character
code does not correspond to a valid character.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
Section 2.5, Standard I/O Streams, fseek(), fsetpos(), read(),
rewind(), setbuf()
The Base Definitions volume of POSIX.1‐2008, <stdio.h>, <wchar.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 UNGETWC(3P)
