UNGETWC(3)                 POSIX Programmer's Manual                UNGETWC(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       ungetwc -- 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.1-2017
       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
       subsequent 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
       calling 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.1-2017, <stdio.h>, <wchar.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  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.opengroup.org/unix/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.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                           UNGETWC(3)
