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UNGETC(3P)                 POSIX Programmer's Manual                UNGETC(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
       ungetc -- push byte back into input stream
SYNOPSIS
       #include <stdio.h>
       int ungetc(int c, 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  ungetc() function shall push the byte specified by c (converted to
       an unsigned char) back onto the input stream pointed to by stream.  The
       pushed-back  bytes 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 bytes for the stream. The external storage correspond-
       ing to the stream shall be unchanged.
       One byte of push-back shall be provided. If ungetc() is called too many
       times  on the same stream without an intervening read or file-position-
       ing operation on that stream, the operation may fail.
       If the value of c equals that of the macro  EOF,  the  operation  shall
       fail and the input stream shall be left unchanged.
       A successful call to ungetc() shall clear the end-of-file indicator for
       the stream. The value of the file-position  indicator  for  the  stream
       after  all  pushed-back  bytes  have been read, or discarded by calling
       fseek(), fseeko(), fsetpos(), or rewind() (but not fflush()), shall  be
       the same as it was before the bytes were pushed back. The file-position
       indicator is decremented by each successful call to  ungetc();  if  its
       value was 0 before a call, its value is unspecified after the call.
RETURN VALUE
       Upon  successful completion, ungetc() shall return the byte pushed back
       after conversion. Otherwise, it shall return EOF.
ERRORS
       No errors are defined.
       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(), getc(), fsetpos(),  read(),
       rewind(), setbuf()
       The Base Definitions volume of POSIX.1-2008, <stdio.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                           UNGETC(3P)