ungetc.c revision 50476 
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 50476 1999-08-28 00:22:10Z peter $";
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#include "libc_private.h"
50
51static int __submore __P((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(fp)
61	register FILE *fp;
62{
63	register int i;
64	register unsigned char *p;
65
66	if (fp->_ub._base == fp->_ubuf) {
67		/*
68		 * Get a new buffer (rather than expanding the old one).
69		 */
70		if ((p = malloc((size_t)BUFSIZ)) == NULL)
71			return (EOF);
72		fp->_ub._base = p;
73		fp->_ub._size = BUFSIZ;
74		p += BUFSIZ - sizeof(fp->_ubuf);
75		for (i = sizeof(fp->_ubuf); --i >= 0;)
76			p[i] = fp->_ubuf[i];
77		fp->_p = p;
78		return (0);
79	}
80	i = fp->_ub._size;
81	p = realloc(fp->_ub._base, (size_t)(i << 1));
82	if (p == NULL)
83		return (EOF);
84	/* no overlap (hence can use memcpy) because we doubled the size */
85	(void)memcpy((void *)(p + i), (void *)p, (size_t)i);
86	fp->_p = p + i;
87	fp->_ub._base = p;
88	fp->_ub._size = i << 1;
89	return (0);
90}
91
92int
93ungetc(c, fp)
94	int c;
95	register FILE *fp;
96{
97	if (c == EOF)
98		return (EOF);
99	if (!__sdidinit)
100		__sinit();
101	FLOCKFILE(fp);
102	if ((fp->_flags & __SRD) == 0) {
103		/*
104		 * Not already reading: no good unless reading-and-writing.
105		 * Otherwise, flush any current write stuff.
106		 */
107		if ((fp->_flags & __SRW) == 0) {
108			FUNLOCKFILE(fp);
109			return (EOF);
110		}
111		if (fp->_flags & __SWR) {
112			if (__sflush(fp)) {
113				FUNLOCKFILE(fp);
114				return (EOF);
115			}
116			fp->_flags &= ~__SWR;
117			fp->_w = 0;
118			fp->_lbfsize = 0;
119		}
120		fp->_flags |= __SRD;
121	}
122	c = (unsigned char)c;
123
124	/*
125	 * If we are in the middle of ungetc'ing, just continue.
126	 * This may require expanding the current ungetc buffer.
127	 */
128	if (HASUB(fp)) {
129		if (fp->_r >= fp->_ub._size && __submore(fp)) {
130			FUNLOCKFILE(fp);
131			return (EOF);
132		}
133		*--fp->_p = c;
134		fp->_r++;
135		FUNLOCKFILE(fp);
136		return (c);
137	}
138	fp->_flags &= ~__SEOF;
139
140	/*
141	 * If we can handle this by simply backing up, do so,
142	 * but never replace the original character.
143	 * (This makes sscanf() work when scanning `const' data.)
144	 */
145	if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
146	    fp->_p[-1] == c) {
147		fp->_p--;
148		fp->_r++;
149		FUNLOCKFILE(fp);
150		return (c);
151	}
152
153	/*
154	 * Create an ungetc buffer.
155	 * Initially, we will use the `reserve' buffer.
156	 */
157	fp->_ur = fp->_r;
158	fp->_up = fp->_p;
159	fp->_ub._base = fp->_ubuf;
160	fp->_ub._size = sizeof(fp->_ubuf);
161	fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
162	fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
163	fp->_r = 1;
164	FUNLOCKFILE(fp);
165	return (c);
166}
167