2 * SPDX-License-Identifier: BSD-3-Clause
4 * Copyright (c) 1990, 1993
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7 * This code is derived from software contributed to Berkeley by
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14 * notice, this list of conditions and the following disclaimer.
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35 #if defined(LIBC_SCCS) && !defined(lint)
36 static char sccsid[] = "@(#)ungetc.c 8.2 (Berkeley) 11/3/93";
37 #endif /* LIBC_SCCS and not lint */
38 #include <sys/cdefs.h>
39 __FBSDID("$FreeBSD$");
41 #include "namespace.h"
45 #include "un-namespace.h"
47 #include "libc_private.h"
49 static int __submore(FILE *);
52 * Expand the ungetc buffer `in place'. That is, adjust fp->_p when
53 * the buffer moves, so that it points the same distance from the end,
54 * and move the bytes in the buffer around as necessary so that they
55 * are all at the end (stack-style).
63 if (fp->_ub._base == fp->_ubuf) {
65 * Get a new buffer (rather than expanding the old one).
67 if ((p = malloc((size_t)BUFSIZ)) == NULL)
70 fp->_ub._size = BUFSIZ;
71 p += BUFSIZ - sizeof(fp->_ubuf);
72 for (i = sizeof(fp->_ubuf); --i >= 0;)
78 p = reallocarray(fp->_ub._base, i, 2);
81 /* no overlap (hence can use memcpy) because we doubled the size */
82 (void)memcpy((void *)(p + i), (void *)p, (size_t)i);
85 fp->_ub._size = i * 2;
93 ungetc(int c, FILE *fp)
99 FLOCKFILE_CANCELSAFE(fp);
101 ret = __ungetc(c, fp);
102 FUNLOCKFILE_CANCELSAFE();
107 * Non-MT-safe version
110 __ungetc(int c, FILE *fp)
115 if ((fp->_flags & __SRD) == 0) {
117 * Not already reading: no good unless reading-and-writing.
118 * Otherwise, flush any current write stuff.
120 if ((fp->_flags & __SRW) == 0)
122 if (fp->_flags & __SWR) {
125 fp->_flags &= ~__SWR;
131 c = (unsigned char)c;
134 * If we are in the middle of ungetc'ing, just continue.
135 * This may require expanding the current ungetc buffer.
138 if (fp->_r >= fp->_ub._size && __submore(fp))
144 fp->_flags &= ~__SEOF;
147 * If we can handle this by simply backing up, do so,
148 * but never replace the original character.
149 * (This makes sscanf() work when scanning `const' data.)
151 if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
159 * Create an ungetc buffer.
160 * Initially, we will use the `reserve' buffer.
164 fp->_ub._base = fp->_ubuf;
165 fp->_ub._size = sizeof(fp->_ubuf);
166 fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
167 fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];