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.

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 .