ungetc.c revision 126808 
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)
38static char sccsid[] = "@(#)ungetc.c	8.2 (Berkeley) 11/3/93";
39#endif /* LIBC_SCCS and not lint */
40#include <sys/cdefs.h>
41__FBSDID("$FreeBSD: head/lib/libc/stdio/ungetc.c 126808 2004-03-10 11:13:23Z tjr $");
42
43#include "namespace.h"
44#include <stdio.h>
45#include <stdlib.h>
46#include <string.h>
47#include "un-namespace.h"
48#include "local.h"
49#include "libc_private.h"
50
51static int __submore(FILE *);
52
53/*
54 * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
55 * the buffer moves, so that it points the same distance from the end,
56 * and move the bytes in the buffer around as necessary so that they
57 * are all at the end (stack-style).
58 */
59static int
60__submore(FILE *fp)
61{
62	int i;
63	unsigned char *p;
64
65	if (fp->_ub._base == fp->_ubuf) {
66		/*
67		 * Get a new buffer (rather than expanding the old one).
68		 */
69		if ((p = malloc((size_t)BUFSIZ)) == NULL)
70			return (EOF);
71		fp->_ub._base = p;
72		fp->_ub._size = BUFSIZ;
73		p += BUFSIZ - sizeof(fp->_ubuf);
74		for (i = sizeof(fp->_ubuf); --i >= 0;)
75			p[i] = fp->_ubuf[i];
76		fp->_p = p;
77		return (0);
78	}
79	i = fp->_ub._size;
80	p = realloc(fp->_ub._base, (size_t)(i << 1));
81	if (p == NULL)
82		return (EOF);
83	/* no overlap (hence can use memcpy) because we doubled the size */
84	(void)memcpy((void *)(p + i), (void *)p, (size_t)i);
85	fp->_p = p + i;
86	fp->_ub._base = p;
87	fp->_ub._size = i << 1;
88	return (0);
89}
90
91/*
92 * MT-safe version
93 */
94int
95ungetc(int c, FILE *fp)
96{
97	int ret;
98
99	if (!__sdidinit)
100		__sinit();
101	FLOCKFILE(fp);
102	ret = __ungetc(c, fp);
103	FUNLOCKFILE(fp);
104	return (ret);
105}
106
107/*
108 * Non-MT-safe version
109 */
110int
111__ungetc(int c, FILE *fp)
112{
113
114	ORIENT(fp, -1);
115
116	if (c == EOF)
117		return (EOF);
118	if ((fp->_flags & __SRD) == 0) {
119		/*
120		 * Not already reading: no good unless reading-and-writing.
121		 * Otherwise, flush any current write stuff.
122		 */
123		if ((fp->_flags & __SRW) == 0)
124			return (EOF);
125		if (fp->_flags & __SWR) {
126			if (__sflush(fp))
127				return (EOF);
128			fp->_flags &= ~__SWR;
129			fp->_w = 0;
130			fp->_lbfsize = 0;
131		}
132		fp->_flags |= __SRD;
133	}
134	c = (unsigned char)c;
135
136	/*
137	 * If we are in the middle of ungetc'ing, just continue.
138	 * This may require expanding the current ungetc buffer.
139	 */
140	if (HASUB(fp)) {
141		if (fp->_r >= fp->_ub._size && __submore(fp))
142			return (EOF);
143		*--fp->_p = c;
144		fp->_r++;
145		return (c);
146	}
147	fp->_flags &= ~__SEOF;
148
149	/*
150	 * If we can handle this by simply backing up, do so,
151	 * but never replace the original character.
152	 * (This makes sscanf() work when scanning `const' data.)
153	 */
154	if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
155	    fp->_p[-1] == c) {
156		fp->_p--;
157		fp->_r++;
158		return (c);
159	}
160
161	/*
162	 * Create an ungetc buffer.
163	 * Initially, we will use the `reserve' buffer.
164	 */
165	fp->_ur = fp->_r;
166	fp->_extra->_up = fp->_p;
167	fp->_ub._base = fp->_ubuf;
168	fp->_ub._size = sizeof(fp->_ubuf);
169	fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
170	fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
171	fp->_r = 1;
172	return (c);
173}
174