xref: /freebsd/lib/libc/stdio/ungetc.c (revision 1e413cf93298b5b97441a21d9a50fdcd0ee9945e)
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  * 4. 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)
34 static char sccsid[] = "@(#)ungetc.c	8.2 (Berkeley) 11/3/93";
35 #endif /* LIBC_SCCS and not lint */
36 #include <sys/cdefs.h>
37 __FBSDID("$FreeBSD$");
38 
39 #include "namespace.h"
40 #include <stdio.h>
41 #include <stdlib.h>
42 #include <string.h>
43 #include "un-namespace.h"
44 #include "local.h"
45 #include "libc_private.h"
46 
47 static int __submore(FILE *);
48 
49 /*
50  * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
51  * the buffer moves, so that it points the same distance from the end,
52  * and move the bytes in the buffer around as necessary so that they
53  * are all at the end (stack-style).
54  */
55 static int
56 __submore(FILE *fp)
57 {
58 	int i;
59 	unsigned char *p;
60 
61 	if (fp->_ub._base == fp->_ubuf) {
62 		/*
63 		 * Get a new buffer (rather than expanding the old one).
64 		 */
65 		if ((p = malloc((size_t)BUFSIZ)) == NULL)
66 			return (EOF);
67 		fp->_ub._base = p;
68 		fp->_ub._size = BUFSIZ;
69 		p += BUFSIZ - sizeof(fp->_ubuf);
70 		for (i = sizeof(fp->_ubuf); --i >= 0;)
71 			p[i] = fp->_ubuf[i];
72 		fp->_p = p;
73 		return (0);
74 	}
75 	i = fp->_ub._size;
76 	p = realloc(fp->_ub._base, (size_t)(i << 1));
77 	if (p == NULL)
78 		return (EOF);
79 	/* no overlap (hence can use memcpy) because we doubled the size */
80 	(void)memcpy((void *)(p + i), (void *)p, (size_t)i);
81 	fp->_p = p + i;
82 	fp->_ub._base = p;
83 	fp->_ub._size = i << 1;
84 	return (0);
85 }
86 
87 /*
88  * MT-safe version
89  */
90 int
91 ungetc(int c, FILE *fp)
92 {
93 	int ret;
94 
95 	if (!__sdidinit)
96 		__sinit();
97 	FLOCKFILE(fp);
98 	ORIENT(fp, -1);
99 	ret = __ungetc(c, fp);
100 	FUNLOCKFILE(fp);
101 	return (ret);
102 }
103 
104 /*
105  * Non-MT-safe version
106  */
107 int
108 __ungetc(int c, FILE *fp)
109 {
110 
111 	if (c == EOF)
112 		return (EOF);
113 	if ((fp->_flags & __SRD) == 0) {
114 		/*
115 		 * Not already reading: no good unless reading-and-writing.
116 		 * Otherwise, flush any current write stuff.
117 		 */
118 		if ((fp->_flags & __SRW) == 0)
119 			return (EOF);
120 		if (fp->_flags & __SWR) {
121 			if (__sflush(fp))
122 				return (EOF);
123 			fp->_flags &= ~__SWR;
124 			fp->_w = 0;
125 			fp->_lbfsize = 0;
126 		}
127 		fp->_flags |= __SRD;
128 	}
129 	c = (unsigned char)c;
130 
131 	/*
132 	 * If we are in the middle of ungetc'ing, just continue.
133 	 * This may require expanding the current ungetc buffer.
134 	 */
135 	if (HASUB(fp)) {
136 		if (fp->_r >= fp->_ub._size && __submore(fp))
137 			return (EOF);
138 		*--fp->_p = c;
139 		fp->_r++;
140 		return (c);
141 	}
142 	fp->_flags &= ~__SEOF;
143 
144 	/*
145 	 * If we can handle this by simply backing up, do so,
146 	 * but never replace the original character.
147 	 * (This makes sscanf() work when scanning `const' data.)
148 	 */
149 	if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
150 	    fp->_p[-1] == c) {
151 		fp->_p--;
152 		fp->_r++;
153 		return (c);
154 	}
155 
156 	/*
157 	 * Create an ungetc buffer.
158 	 * Initially, we will use the `reserve' buffer.
159 	 */
160 	fp->_ur = fp->_r;
161 	fp->_extra->_up = fp->_p;
162 	fp->_ub._base = fp->_ubuf;
163 	fp->_ub._size = sizeof(fp->_ubuf);
164 	fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
165 	fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
166 	fp->_r = 1;
167 	return (c);
168 }
169