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ungetc(3posix)


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.12008
   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
   corresponding 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-
   positioning 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.12008, <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
   Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .



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