ungetc.c revision 1.8 
1/*-
2 * Copyright (c) 1990, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * This code is derived from software contributed to Berkeley by
6 * Chris Torek.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 *    notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 * 3. Neither the name of the University nor the names of its contributors
17 *    may be used to endorse or promote products derived from this software
18 *    without specific prior written permission.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 */
32
33#if defined(LIBC_SCCS) && !defined(lint)
34static char rcsid[] = "$OpenBSD: ungetc.c,v 1.8 2005/06/17 20:40:32 espie Exp $";
35#endif /* LIBC_SCCS and not lint */
36
37#include <stdio.h>
38#include <stdlib.h>
39#include <string.h>
40#include "local.h"
41
42static int __submore(FILE *);
43/*
44 * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
45 * the buffer moves, so that it points the same distance from the end,
46 * and move the bytes in the buffer around as necessary so that they
47 * are all at the end (stack-style).
48 */
49static int
50__submore(FILE *fp)
51{
52	int i;
53	unsigned char *p;
54
55	if (_UB(fp)._base == fp->_ubuf) {
56		/*
57		 * Get a new buffer (rather than expanding the old one).
58		 */
59		if ((p = malloc((size_t)BUFSIZ)) == NULL)
60			return (EOF);
61		_UB(fp)._base = p;
62		_UB(fp)._size = BUFSIZ;
63		p += BUFSIZ - sizeof(fp->_ubuf);
64		for (i = sizeof(fp->_ubuf); --i >= 0;)
65			p[i] = fp->_ubuf[i];
66		fp->_p = p;
67		return (0);
68	}
69	i = _UB(fp)._size;
70	p = realloc(_UB(fp)._base, i << 1);
71	if (p == NULL)
72		return (EOF);
73	/* no overlap (hence can use memcpy) because we doubled the size */
74	(void)memcpy((void *)(p + i), (void *)p, (size_t)i);
75	fp->_p = p + i;
76	_UB(fp)._base = p;
77	_UB(fp)._size = i << 1;
78	return (0);
79}
80
81int
82ungetc(int c, FILE *fp)
83{
84	if (c == EOF)
85		return (EOF);
86	if (!__sdidinit)
87		__sinit();
88	_SET_ORIENTATION(fp, -1);
89	if ((fp->_flags & __SRD) == 0) {
90		/*
91		 * Not already reading: no good unless reading-and-writing.
92		 * Otherwise, flush any current write stuff.
93		 */
94		if ((fp->_flags & __SRW) == 0)
95			return (EOF);
96		if (fp->_flags & __SWR) {
97			if (__sflush(fp))
98				return (EOF);
99			fp->_flags &= ~__SWR;
100			fp->_w = 0;
101			fp->_lbfsize = 0;
102		}
103		fp->_flags |= __SRD;
104	}
105	c = (unsigned char)c;
106
107	/*
108	 * If we are in the middle of ungetc'ing, just continue.
109	 * This may require expanding the current ungetc buffer.
110	 */
111	if (HASUB(fp)) {
112		if (fp->_r >= _UB(fp)._size && __submore(fp))
113			return (EOF);
114		*--fp->_p = c;
115		fp->_r++;
116		return (c);
117	}
118	fp->_flags &= ~__SEOF;
119
120	/*
121	 * If we can handle this by simply backing up, do so,
122	 * but never replace the original character.
123	 * (This makes sscanf() work when scanning `const' data.)
124	 */
125	if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
126	    fp->_p[-1] == c) {
127		fp->_p--;
128		fp->_r++;
129		return (c);
130	}
131
132	/*
133	 * Create an ungetc buffer.
134	 * Initially, we will use the `reserve' buffer.
135	 */
136	fp->_ur = fp->_r;
137	fp->_up = fp->_p;
138	_UB(fp)._base = fp->_ubuf;
139	_UB(fp)._size = sizeof(fp->_ubuf);
140	fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
141	fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
142	fp->_r = 1;
143	return (c);
144}
145