ungetc.c revision 1.5 
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 1.5 2003/06/02 20:18:37 millert 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(fp)
51	FILE *fp;
52{
53	register int i;
54	register unsigned char *p;
55
56	if (fp->_ub._base == fp->_ubuf) {
57		/*
58		 * Get a new buffer (rather than expanding the old one).
59		 */
60		if ((p = malloc((size_t)BUFSIZ)) == NULL)
61			return (EOF);
62		fp->_ub._base = p;
63		fp->_ub._size = BUFSIZ;
64		p += BUFSIZ - sizeof(fp->_ubuf);
65		for (i = sizeof(fp->_ubuf); --i >= 0;)
66			p[i] = fp->_ubuf[i];
67		fp->_p = p;
68		return (0);
69	}
70	i = fp->_ub._size;
71	p = realloc(fp->_ub._base, i << 1);
72	if (p == NULL)
73		return (EOF);
74	/* no overlap (hence can use memcpy) because we doubled the size */
75	(void)memcpy((void *)(p + i), (void *)p, (size_t)i);
76	fp->_p = p + i;
77	fp->_ub._base = p;
78	fp->_ub._size = i << 1;
79	return (0);
80}
81
82int
83ungetc(c, fp)
84	int c;
85	register FILE *fp;
86{
87	if (c == EOF)
88		return (EOF);
89	if (!__sdidinit)
90		__sinit();
91	if ((fp->_flags & __SRD) == 0) {
92		/*
93		 * Not already reading: no good unless reading-and-writing.
94		 * Otherwise, flush any current write stuff.
95		 */
96		if ((fp->_flags & __SRW) == 0)
97			return (EOF);
98		if (fp->_flags & __SWR) {
99			if (__sflush(fp))
100				return (EOF);
101			fp->_flags &= ~__SWR;
102			fp->_w = 0;
103			fp->_lbfsize = 0;
104		}
105		fp->_flags |= __SRD;
106	}
107	c = (unsigned char)c;
108
109	/*
110	 * If we are in the middle of ungetc'ing, just continue.
111	 * This may require expanding the current ungetc buffer.
112	 */
113	if (HASUB(fp)) {
114		if (fp->_r >= fp->_ub._size && __submore(fp))
115			return (EOF);
116		*--fp->_p = c;
117		fp->_r++;
118		return (c);
119	}
120	fp->_flags &= ~__SEOF;
121
122	/*
123	 * If we can handle this by simply backing up, do so,
124	 * but never replace the original character.
125	 * (This makes sscanf() work when scanning `const' data.)
126	 */
127	if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
128	    fp->_p[-1] == c) {
129		fp->_p--;
130		fp->_r++;
131		return (c);
132	}
133
134	/*
135	 * Create an ungetc buffer.
136	 * Initially, we will use the `reserve' buffer.
137	 */
138	fp->_ur = fp->_r;
139	fp->_up = fp->_p;
140	fp->_ub._base = fp->_ubuf;
141	fp->_ub._size = sizeof(fp->_ubuf);
142	fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
143	fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
144	fp->_r = 1;
145	return (c);
146}
147