ungetc.c revision 16586 
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		"$Id$";
43#endif /* LIBC_SCCS and not lint */
44
45#include <stdio.h>
46#include <stdlib.h>
47#include <string.h>
48#include "local.h"
49#ifdef _THREAD_SAFE
50#include <pthread.h>
51#include "pthread_private.h"
52#endif
53
54static int __submore __P((FILE *));
55
56/*
57 * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
58 * the buffer moves, so that it points the same distance from the end,
59 * and move the bytes in the buffer around as necessary so that they
60 * are all at the end (stack-style).
61 */
62static int
63__submore(fp)
64	register FILE *fp;
65{
66	register int i;
67	register unsigned char *p;
68
69	if (fp->_ub._base == fp->_ubuf) {
70		/*
71		 * Get a new buffer (rather than expanding the old one).
72		 */
73		if ((p = malloc((size_t)BUFSIZ)) == NULL)
74			return (EOF);
75		fp->_ub._base = p;
76		fp->_ub._size = BUFSIZ;
77		p += BUFSIZ - sizeof(fp->_ubuf);
78		for (i = sizeof(fp->_ubuf); --i >= 0;)
79			p[i] = fp->_ubuf[i];
80		fp->_p = p;
81		return (0);
82	}
83	i = fp->_ub._size;
84	p = realloc(fp->_ub._base, (size_t)(i << 1));
85	if (p == NULL)
86		return (EOF);
87	/* no overlap (hence can use memcpy) because we doubled the size */
88	(void)memcpy((void *)(p + i), (void *)p, (size_t)i);
89	fp->_p = p + i;
90	fp->_ub._base = p;
91	fp->_ub._size = i << 1;
92	return (0);
93}
94
95int
96ungetc(c, fp)
97	int c;
98	register FILE *fp;
99{
100	if (c == EOF)
101		return (EOF);
102	if (!__sdidinit)
103		__sinit();
104#ifdef _THREAD_SAFE
105	_thread_flockfile(fp,__FILE__,__LINE__);
106#endif
107	if ((fp->_flags & __SRD) == 0) {
108		/*
109		 * Not already reading: no good unless reading-and-writing.
110		 * Otherwise, flush any current write stuff.
111		 */
112		if ((fp->_flags & __SRW) == 0) {
113#ifdef _THREAD_SAFE
114			_thread_funlockfile(fp);
115#endif
116			return (EOF);
117		}
118		if (fp->_flags & __SWR) {
119			if (__sflush(fp)) {
120#ifdef _THREAD_SAFE
121				_thread_funlockfile(fp);
122#endif
123				return (EOF);
124			}
125			fp->_flags &= ~__SWR;
126			fp->_w = 0;
127			fp->_lbfsize = 0;
128		}
129		fp->_flags |= __SRD;
130	}
131	c = (unsigned char)c;
132
133	/*
134	 * If we are in the middle of ungetc'ing, just continue.
135	 * This may require expanding the current ungetc buffer.
136	 */
137	if (HASUB(fp)) {
138		if (fp->_r >= fp->_ub._size && __submore(fp)) {
139#ifdef _THREAD_SAFE
140			_thread_funlockfile(fp);
141#endif
142			return (EOF);
143		}
144		*--fp->_p = c;
145		fp->_r++;
146#ifdef _THREAD_SAFE
147		_thread_funlockfile(fp);
148#endif
149		return (c);
150	}
151	fp->_flags &= ~__SEOF;
152
153	/*
154	 * If we can handle this by simply backing up, do so,
155	 * but never replace the original character.
156	 * (This makes sscanf() work when scanning `const' data.)
157	 */
158	if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
159	    fp->_p[-1] == c) {
160		fp->_p--;
161		fp->_r++;
162#ifdef _THREAD_SAFE
163		_thread_funlockfile(fp);
164#endif
165		return (c);
166	}
167
168	/*
169	 * Create an ungetc buffer.
170	 * Initially, we will use the `reserve' buffer.
171	 */
172	fp->_ur = fp->_r;
173	fp->_up = fp->_p;
174	fp->_ub._base = fp->_ubuf;
175	fp->_ub._size = sizeof(fp->_ubuf);
176	fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
177	fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
178	fp->_r = 1;
179#ifdef _THREAD_SAFE
180	_thread_funlockfile(fp);
181#endif
182	return (c);
183}
184