ungetc.c revision 82709 
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. All advertising materials mentioning features or use of this software
17 *    must display the following acknowledgement:
18 *	This product includes software developed by the University of
19 *	California, Berkeley and its contributors.
20 * 4. Neither the name of the University nor the names of its contributors
21 *    may be used to endorse or promote products derived from this software
22 *    without specific prior written permission.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * SUCH DAMAGE.
35 */
36
37#if defined(LIBC_SCCS) && !defined(lint)
38#if 0
39static char sccsid[] = "@(#)ungetc.c	8.2 (Berkeley) 11/3/93";
40#endif
41static const char rcsid[] =
42  "$FreeBSD: head/lib/libc/stdio/ungetc.c 82709 2001-09-01 01:56:54Z ache $";
43#endif /* LIBC_SCCS and not lint */
44
45#include "namespace.h"
46#include <stdio.h>
47#include <stdlib.h>
48#include <string.h>
49#include "un-namespace.h"
50#include "local.h"
51#include "libc_private.h"
52
53static int __submore __P((FILE *));
54
55/*
56 * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
57 * the buffer moves, so that it points the same distance from the end,
58 * and move the bytes in the buffer around as necessary so that they
59 * are all at the end (stack-style).
60 */
61static int
62__submore(FILE *fp)
63{
64	int i;
65	unsigned char *p;
66
67	if (fp->_ub._base == fp->_ubuf) {
68		/*
69		 * Get a new buffer (rather than expanding the old one).
70		 */
71		if ((p = malloc((size_t)BUFSIZ)) == NULL)
72			return (EOF);
73		fp->_ub._base = p;
74		fp->_ub._size = BUFSIZ;
75		p += BUFSIZ - sizeof(fp->_ubuf);
76		for (i = sizeof(fp->_ubuf); --i >= 0;)
77			p[i] = fp->_ubuf[i];
78		fp->_p = p;
79		return (0);
80	}
81	i = fp->_ub._size;
82	p = realloc(fp->_ub._base, (size_t)(i << 1));
83	if (p == NULL)
84		return (EOF);
85	/* no overlap (hence can use memcpy) because we doubled the size */
86	(void)memcpy((void *)(p + i), (void *)p, (size_t)i);
87	fp->_p = p + i;
88	fp->_ub._base = p;
89	fp->_ub._size = i << 1;
90	return (0);
91}
92
93/*
94 * MT-safe version
95 */
96int
97ungetc(int c, FILE *fp)
98{
99	int ret;
100
101	if (c == EOF)
102		return (EOF);
103	if (!__sdidinit)
104		__sinit();
105	FLOCKFILE(fp);
106	ret = __ungetc(c, fp);
107	FUNLOCKFILE(fp);
108	return (ret);
109}
110
111/*
112 * Non-MT-safe version
113 */
114int
115__ungetc(int c, FILE *fp)
116{
117	if (c == EOF)
118		return (EOF);
119	if ((fp->_flags & __SRD) == 0) {
120		/*
121		 * Not already reading: no good unless reading-and-writing.
122		 * Otherwise, flush any current write stuff.
123		 */
124		if ((fp->_flags & __SRW) == 0)
125			return (EOF);
126		if (fp->_flags & __SWR) {
127			if (__sflush(fp))
128				return (EOF);
129			fp->_flags &= ~__SWR;
130			fp->_w = 0;
131			fp->_lbfsize = 0;
132		}
133		fp->_flags |= __SRD;
134	}
135	c = (unsigned char)c;
136
137	/*
138	 * If we are in the middle of ungetc'ing, just continue.
139	 * This may require expanding the current ungetc buffer.
140	 */
141	if (HASUB(fp)) {
142		if (fp->_r >= fp->_ub._size && __submore(fp))
143			return (EOF);
144		*--fp->_p = c;
145		fp->_r++;
146		return (c);
147	}
148	fp->_flags &= ~__SEOF;
149
150	/*
151	 * If we can handle this by simply backing up, do so,
152	 * but never replace the original character.
153	 * (This makes sscanf() work when scanning `const' data.)
154	 */
155	if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
156	    fp->_p[-1] == c) {
157		fp->_p--;
158		fp->_r++;
159		return (c);
160	}
161
162	/*
163	 * Create an ungetc buffer.
164	 * Initially, we will use the `reserve' buffer.
165	 */
166	fp->_ur = fp->_r;
167	fp->_extra->_up = fp->_p;
168	fp->_ub._base = fp->_ubuf;
169	fp->_ub._size = sizeof(fp->_ubuf);
170	fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
171	fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
172	fp->_r = 1;
173	return (c);
174}
175