ungetc.c revision 331722 
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 sccsid[] = "@(#)ungetc.c	8.2 (Berkeley) 11/3/93";
35#endif /* LIBC_SCCS and not lint */
36#include <sys/cdefs.h>
37__FBSDID("$FreeBSD: stable/11/lib/libc/stdio/ungetc.c 331722 2018-03-29 02:50:57Z eadler $");
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
47static 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 */
55static 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 = reallocarray(fp->_ub._base, i, 2);
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 * 2;
84	return (0);
85}
86
87/*
88 * MT-safe version
89 */
90int
91ungetc(int c, FILE *fp)
92{
93	int ret;
94
95	if (!__sdidinit)
96		__sinit();
97	FLOCKFILE_CANCELSAFE(fp);
98	ORIENT(fp, -1);
99	ret = __ungetc(c, fp);
100	FUNLOCKFILE_CANCELSAFE();
101	return (ret);
102}
103
104/*
105 * Non-MT-safe version
106 */
107int
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->_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