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---
ungetc.c (4503B)
---
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 static char rcsid[] = "$OpenBSD: ungetc.c,v 1.2 1996/08/19 08:33:11 tholo Exp $";
39 #endif /* LIBC_SCCS and not lint */
40
41 #include <stdio.h>
42 #include <stdlib.h>
43 #include <string.h>
44 #include "local.h"
45
46 /*
47 * Expand the ungetc buffer `in place'. That is, adjust fp->_p when
48 * the buffer moves, so that it points the same distance from the end,
49 * and move the bytes in the buffer around as necessary so that they
50 * are all at the end (stack-style).
51 */
52 static int
53 __submore(fp)
54 register FILE *fp;
55 {
56 register int i;
57 register unsigned char *p;
58
59 if (fp->_ub._base == fp->_ubuf) {
60 /*
61 * Get a new buffer (rather than expanding the old one).
62 */
63 if ((p = malloc((size_t)BUFSIZ)) == NULL)
64 return (EOF);
65 fp->_ub._base = p;
66 fp->_ub._size = BUFSIZ;
67 p += BUFSIZ - sizeof(fp->_ubuf);
68 for (i = sizeof(fp->_ubuf); --i >= 0;)
69 p[i] = fp->_ubuf[i];
70 fp->_p = p;
71 return (0);
72 }
73 i = fp->_ub._size;
74 p = realloc(fp->_ub._base, i << 1);
75 if (p == NULL)
76 return (EOF);
77 /* no overlap (hence can use memcpy) because we doubled the size */
78 (void)memcpy((void *)(p + i), (void *)p, (size_t)i);
79 fp->_p = p + i;
80 fp->_ub._base = p;
81 fp->_ub._size = i << 1;
82 return (0);
83 }
84
85 int
86 ungetc(c, fp)
87 int c;
88 register FILE *fp;
89 {
90 if (c == EOF)
91 return (EOF);
92 if (!__sdidinit)
93 __sinit();
94 if ((fp->_flags & __SRD) == 0) {
95 /*
96 * Not already reading: no good unless reading-and-writing.
97 * Otherwise, flush any current write stuff.
98 */
99 if ((fp->_flags & __SRW) == 0)
100 return (EOF);
101 if (fp->_flags & __SWR) {
102 if (__sflush(fp))
103 return (EOF);
104 fp->_flags &= ~__SWR;
105 fp->_w = 0;
106 fp->_lbfsize = 0;
107 }
108 fp->_flags |= __SRD;
109 }
110 c = (unsigned char)c;
111
112 /*
113 * If we are in the middle of ungetc'ing, just continue.
114 * This may require expanding the current ungetc buffer.
115 */
116 if (HASUB(fp)) {
117 if (fp->_r >= fp->_ub._size && __submore(fp))
118 return (EOF);
119 *--fp->_p = c;
120 fp->_r++;
121 return (c);
122 }
123 fp->_flags &= ~__SEOF;
124
125 /*
126 * If we can handle this by simply backing up, do so,
127 * but never replace the original character.
128 * (This makes sscanf() work when scanning `const' data.)
129 */
130 if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
131 fp->_p[-1] == c) {
132 fp->_p--;
133 fp->_r++;
134 return (c);
135 }
136
137 /*
138 * Create an ungetc buffer.
139 * Initially, we will use the `reserve' buffer.
140 */
141 fp->_ur = fp->_r;
142 fp->_up = fp->_p;
143 fp->_ub._base = fp->_ubuf;
144 fp->_ub._size = sizeof(fp->_ubuf);
145 fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
146 fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
147 fp->_r = 1;
148 return (c);
149 }