text: /*
   * $Id: stdio_ungetc.c,v 1.7 2006-01-08 12:04:25 obarthel Exp $
   *
   * :ts=4
   *
   * Portable ISO 'C' (1994) runtime library for the Amiga computer
   * Copyright (c) 2002-2015 by Olaf Barthel <obarthel (at) gmx.net>
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   *   - Redistributions of source code must retain the above copyright
   *     notice, this list of conditions and the following disclaimer.
   *
   *   - Neither the name of Olaf Barthel nor the names of contributors
   *     may be used to endorse or promote products derived from this
   *     software without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
   * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
   * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   * POSSIBILITY OF SUCH DAMAGE.
   */
  
  #ifndef _STDLIB_NULL_POINTER_CHECK_H
  #include "stdlib_null_pointer_check.h"
  #endif /* _STDLIB_NULL_POINTER_CHECK_H */
  
  /****************************************************************************/
  
  #ifndef _STDIO_HEADERS_H
  #include "stdio_headers.h"
  #endif /* _STDIO_HEADERS_H */
  
  /****************************************************************************/
  
  int
  ungetc(int c,FILE *stream)
  {
  	struct iob * file = (struct iob *)stream;
  	int result = EOF;
  
  	assert( stream != NULL );
  
  	if(__check_abort_enabled)
  		__check_abort();
  
  	flockfile(stream);
  
  	#if defined(CHECK_FOR_NULL_POINTERS)
  	{
  		if(stream == NULL)
  		{
  			SHOWMSG("null file pointer!");
  
  			__set_errno(EFAULT);
  			goto out;
  		}
  	}
  	#endif /* CHECK_FOR_NULL_POINTERS */
  
  	assert( __is_valid_iob(file) );
  	assert( FLAG_IS_SET(file->iob_Flags,IOBF_IN_USE) );
  	assert( file->iob_BufferSize > 0 );
  
  	if(FLAG_IS_CLEAR(file->iob_Flags,IOBF_IN_USE))
  	{
  		SHOWMSG("this file is not even in use");
  
  		SET_FLAG(file->iob_Flags,IOBF_ERROR);
  
  		__set_errno(EBADF);
  
  		goto out;
  	}
  
  	/* Pushing back characters only works for files that can be read from. */
  	if(FLAG_IS_CLEAR(file->iob_Flags,IOBF_READ))
  	{
  		SHOWMSG("can't even read from this file");
  
  		SET_FLAG(file->iob_Flags,IOBF_ERROR);
  
  		__set_errno(EACCES);
  
  		goto out;
  	}
  
  	/* Pushing back an EOF is forbidden. */
  	if(c == EOF)
  	{
  		SHOWMSG("cannot push back an EOF");
  
  		SET_FLAG(file->iob_Flags,IOBF_ERROR);
  
  		__set_errno(EINVAL);
  
  		goto out;
  	}
  
  	/* Get rid of the write buffer, if it's still around. */
  	if(__iob_write_buffer_is_valid(file) > 0 && __flush_iob_write_buffer(file) < 0)
  	{
  		SHOWMSG("could not flush write buffer");
  		goto out;
  	}
  
  	/* We need to replace one of the characters in the buffer, which must
  	 * have been read before. The ISO standard requires that it must
  	 * be possible to push back at least one single character.
  	 */
  	if(file->iob_BufferPosition == 0)
  	{
  		SHOWMSG("no room to push back");
  
  		SET_FLAG(file->iob_Flags,IOBF_ERROR);
  
  		__set_errno(ENOBUFS);
  
  		goto out;
  	}
  
  	CLEAR_FLAG(file->iob_Flags,IOBF_EOF_REACHED);
  
  	/* Replace the character just read. */
  	file->iob_Buffer[--file->iob_BufferPosition] = c;
  
  	/* Clamp the result to an unsigned 8 bit value. */
  	result = (c & 255);
  
   out:
  
  	funlockfile(stream);
  
  	return(result);
  }
  