1 /* $OpenBSD: ungetc.c,v 1.15 2016/09/21 04:38:56 guenther Exp $ */
2 /*-
3 * Copyright (c) 1990, 1993
4 * The Regents of the University of California. All rights reserved.
5 *
6 * This code is derived from software contributed to Berkeley by
7 * Chris Torek.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 * 3. Neither the name of the University nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34 #include <stdio.h>
35 #include <stdlib.h>
36 #include <string.h>
37 #include "local.h"
38
39 static int __submore(FILE *);
40 /*
41 * Expand the ungetc buffer `in place'. That is, adjust fp->_p when
42 * the buffer moves, so that it points the same distance from the end,
43 * and move the bytes in the buffer around as necessary so that they
44 * are all at the end (stack-style).
45 */
46 static int
__submore(FILE * fp)47 __submore(FILE *fp)
48 {
49 int i;
50 unsigned char *p;
51
52 if (_UB(fp)._base == fp->_ubuf) {
53 /*
54 * Get a new buffer (rather than expanding the old one).
55 */
56 if ((p = malloc(BUFSIZ)) == NULL)
57 return (EOF);
58 _UB(fp)._base = p;
59 _UB(fp)._size = BUFSIZ;
60 p += BUFSIZ - sizeof(fp->_ubuf);
61 for (i = sizeof(fp->_ubuf); --i >= 0;)
62 p[i] = fp->_ubuf[i];
63 fp->_p = p;
64 return (0);
65 }
66 i = _UB(fp)._size;
67 p = reallocarray(_UB(fp)._base, i, 2);
68 if (p == NULL)
69 return (EOF);
70 /* no overlap (hence can use memcpy) because we doubled the size */
71 (void)memcpy(p + i, p, i);
72 fp->_p = p + i;
73 _UB(fp)._base = p;
74 _UB(fp)._size = i * 2;
75 return (0);
76 }
77
78 int
ungetc(int c,FILE * fp)79 ungetc(int c, FILE *fp)
80 {
81 if (c == EOF)
82 return (EOF);
83 if (!__sdidinit)
84 __sinit();
85 FLOCKFILE(fp);
86 _SET_ORIENTATION(fp, -1);
87 if ((fp->_flags & __SRD) == 0) {
88 /*
89 * Not already reading: no good unless reading-and-writing.
90 * Otherwise, flush any current write stuff.
91 */
92 if ((fp->_flags & __SRW) == 0) {
93 error: FUNLOCKFILE(fp);
94 return (EOF);
95 }
96 if (fp->_flags & __SWR) {
97 if (__sflush(fp))
98 goto error;
99 fp->_flags &= ~__SWR;
100 fp->_w = 0;
101 fp->_lbfsize = 0;
102 }
103 fp->_flags |= __SRD;
104 }
105 c = (unsigned char)c;
106
107 /*
108 * If we are in the middle of ungetc'ing, just continue.
109 * This may require expanding the current ungetc buffer.
110 */
111 if (HASUB(fp)) {
112 if (fp->_r >= _UB(fp)._size && __submore(fp))
113 goto error;
114 *--fp->_p = c;
115 inc_ret: fp->_r++;
116 FUNLOCKFILE(fp);
117 return (c);
118 }
119 fp->_flags &= ~__SEOF;
120
121 /*
122 * If we can handle this by simply backing up, do so,
123 * but never replace the original character.
124 * (This makes sscanf() work when scanning `const' data.)
125 */
126 if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
127 fp->_p[-1] == c) {
128 fp->_p--;
129 goto inc_ret;
130 }
131
132 /*
133 * Create an ungetc buffer.
134 * Initially, we will use the `reserve' buffer.
135 */
136 fp->_ur = fp->_r;
137 fp->_up = fp->_p;
138 _UB(fp)._base = fp->_ubuf;
139 _UB(fp)._size = sizeof(fp->_ubuf);
140 fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
141 fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
142 fp->_r = 1;
143 FUNLOCKFILE(fp);
144 return (c);
145 }
146 DEF_STRONG(ungetc);
147