ungetwc(3p) — Linux manual page

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.

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(3p), fsetpos(3p),
       read(3p), rewind(3p), setbuf(3p)

       The Base Definitions volume of POSIX.1‐2017, stdio.h(0p),
       wchar.h(0p)

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(3P)

Pages that refer to this page: wchar.h(0p)

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