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 (con-
       sult 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  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(), fsetpos(), or rewind()) 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  indi-
       cator  for the stream after reading or discarding all pushed-back bytes 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
       fseek(), getc(), fsetpos(), read(), rewind(), setbuf(), the Base Definitions volume of IEEE Std 1003.1-2001, <stdio.h>

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (C) 2001-2003 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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                    UNGETC(3P)