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/*
* Copyright (c) 1990 The Regents of the University of California.
* All rights reserved.
*
* Redistribution and use in source and binary forms are permitted
* provided that the above copyright notice and this paragraph are
* duplicated in all such forms and that any documentation,
* and/or other materials related to such
* distribution and use acknowledge that the software was developed
* by the University of California, Berkeley. The name of the
* University may not be used to endorse or promote products derived
* from this software without specific prior written permission.
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*/
/*
FUNCTION
<<ungetc>>---push data back into a stream
INDEX
ungetc
INDEX
_ungetc_r
SYNOPSIS
#include <stdio.h>
int ungetc(int <[c]>, FILE *<[stream]>);
int ungetc( int <[c]>, FILE *<[stream]>);
DESCRIPTION
<<ungetc>> is used to return bytes back to <[stream]> to be read again.
If <[c]> is EOF, the stream is unchanged. Otherwise, the unsigned
char <[c]> is put back on the stream, and subsequent reads will see
the bytes pushed back in reverse order. Pushed byes are lost if the
stream is repositioned, such as by <<fseek>>, <<fsetpos>>, or
<<rewind>>.
The underlying file is not changed, but it is possible to push back
something different than what was originally read. Ungetting a
character will clear the end-of-stream marker, and decrement the file
position indicator. Pushing back beyond the beginning of a file gives
unspecified behavior.
The alternate function <<_ungetc_r>> is a reentrant version. The
extra argument <[reent]> is a pointer to a reentrancy structure.
RETURNS
The character pushed back, or <<EOF>> on error.
PORTABILITY
ANSI C requires <<ungetc>>, but only requires a pushback buffer of one
byte; although this implementation can handle multiple bytes, not all
can. Pushing back a signed char is a common application bug.
Supporting OS subroutines required: <<sbrk>>.
*/
#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "%W% (Berkeley) %G%";
#endif /* LIBC_SCCS and not lint */
#define _DEFAULT_SOURCE
#include <_ansi.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "local.h"
/*
* Expand the ungetc buffer `in place'. That is, adjust fp->_p when
* the buffer moves, so that it points the same distance from the end,
* and move the bytes in the buffer around as necessary so that they
* are all at the end (stack-style).
*/
/*static*/
int
__submore (
register FILE *fp)
{
register int i;
register unsigned char *p;
if (fp->_ub._base == fp->_ubuf)
{
/*
* Get a new buffer (rather than expanding the old one).
*/
if ((p = (unsigned char *) malloc ((size_t) BUFSIZ)) == NULL)
return EOF;
fp->_ub._base = p;
fp->_ub._size = BUFSIZ;
p += BUFSIZ - sizeof (fp->_ubuf);
for (i = sizeof (fp->_ubuf); --i >= 0;)
p[i] = fp->_ubuf[i];
fp->_p = p;
return 0;
}
i = fp->_ub._size;
p = (unsigned char *) realloc ((void *) (fp->_ub._base), i << 1);
if (p == NULL)
return EOF;
(void) memcpy ((void *) (p + i), (void *) p, (size_t) i);
fp->_p = p + i;
fp->_ub._base = p;
fp->_ub._size = i << 1;
return 0;
}
int
ungetc (
int c,
register FILE *fp)
{
if (c == EOF)
return (EOF);
/* Ensure stdio has been initialized.
??? Might be able to remove this as some other stdio routine should
have already been called to get the char we are un-getting. */
CHECK_INIT (rptr, fp);
_newlib_flockfile_start (fp);
ORIENT (fp, -1);
/* After ungetc, we won't be at eof anymore */
fp->_flags &= ~__SEOF;
if ((fp->_flags & __SRD) == 0)
{
/*
* Not already reading: no good unless reading-and-writing.
* Otherwise, flush any current write stuff.
*/
if ((fp->_flags & __SRW) == 0)
{
_newlib_flockfile_exit (fp);
return EOF;
}
if (fp->_flags & __SWR)
{
if (fflush ( fp))
{
_newlib_flockfile_exit (fp);
return EOF;
}
fp->_flags &= ~__SWR;
fp->_w = 0;
fp->_lbfsize = 0;
}
fp->_flags |= __SRD;
}
c = (unsigned char) c;
/*
* If we are in the middle of ungetc'ing, just continue.
* This may require expanding the current ungetc buffer.
*/
if (HASUB (fp))
{
if (fp->_r >= fp->_ub._size && __submore (fp))
{
_newlib_flockfile_exit (fp);
return EOF;
}
*--fp->_p = c;
fp->_r++;
_newlib_flockfile_exit (fp);
return c;
}
/*
* If we can handle this by simply backing up, do so,
* but never replace the original character.
* (This makes sscanf() work when scanning `const' data.)
*/
if (fp->_bf._base != NULL && fp->_p > fp->_bf._base && fp->_p[-1] == c)
{
fp->_p--;
fp->_r++;
_newlib_flockfile_exit (fp);
return c;
}
/*
* Create an ungetc buffer.
* Initially, we will use the `reserve' buffer.
*/
fp->_ur = fp->_r;
fp->_up = fp->_p;
fp->_ub._base = fp->_ubuf;
fp->_ub._size = sizeof (fp->_ubuf);
fp->_ubuf[sizeof (fp->_ubuf) - 1] = c;
fp->_p = &fp->_ubuf[sizeof (fp->_ubuf) - 1];
fp->_r = 1;
_newlib_flockfile_end (fp);
return c;
}
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