ungetc.c revision 1573 
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)
38static char sccsid[] = "@(#)ungetc.c	8.2 (Berkeley) 11/3/93";
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 */
52static
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
85ungetc(c, fp)
86	int c;
87	register FILE *fp;
88{
89	if (c == EOF)
90		return (EOF);
91	if (!__sdidinit)
92		__sinit();
93	if ((fp->_flags & __SRD) == 0) {
94		/*
95		 * Not already reading: no good unless reading-and-writing.
96		 * Otherwise, flush any current write stuff.
97		 */
98		if ((fp->_flags & __SRW) == 0)
99			return (EOF);
100		if (fp->_flags & __SWR) {
101			if (__sflush(fp))
102				return (EOF);
103			fp->_flags &= ~__SWR;
104			fp->_w = 0;
105			fp->_lbfsize = 0;
106		}
107		fp->_flags |= __SRD;
108	}
109	c = (unsigned char)c;
110
111	/*
112	 * If we are in the middle of ungetc'ing, just continue.
113	 * This may require expanding the current ungetc buffer.
114	 */
115	if (HASUB(fp)) {
116		if (fp->_r >= fp->_ub._size && __submore(fp))
117			return (EOF);
118		*--fp->_p = c;
119		fp->_r++;
120		return (c);
121	}
122	fp->_flags &= ~__SEOF;
123
124	/*
125	 * If we can handle this by simply backing up, do so,
126	 * but never replace the original character.
127	 * (This makes sscanf() work when scanning `const' data.)
128	 */
129	if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
130	    fp->_p[-1] == c) {
131		fp->_p--;
132		fp->_r++;
133		return (c);
134	}
135
136	/*
137	 * Create an ungetc buffer.
138	 * Initially, we will use the `reserve' buffer.
139	 */
140	fp->_ur = fp->_r;
141	fp->_up = fp->_p;
142	fp->_ub._base = fp->_ubuf;
143	fp->_ub._size = sizeof(fp->_ubuf);
144	fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
145	fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
146	fp->_r = 1;
147	return (c);
148}
149