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36 * @(#)ungetc.c 8.2 (Berkeley) 11/3/93
37 * $FreeBSD: src/lib/libc/stdio/ungetc.c,v 1.7.2.1 2001/03/05 11:27:49 obrien Exp $
38 * $DragonFly: src/lib/libc/stdio/ungetc.c,v 1.7 2005/07/23 23:14:44 joerg Exp $
41 #include "namespace.h"
45 #include "un-namespace.h"
48 #include "libc_private.h"
49 #include "priv_stdio.h"
51 static int __submore (FILE *);
54 * Expand the ungetc buffer `in place'. That is, adjust fp->_p when
55 * the buffer moves, so that it points the same distance from the end,
56 * and move the bytes in the buffer around as necessary so that they
57 * are all at the end (stack-style).
65 if (fp->_ub._base == fp->_ubuf) {
67 * Get a new buffer (rather than expanding the old one).
69 if ((p = malloc((size_t)BUFSIZ)) == NULL)
72 fp->_ub._size = BUFSIZ;
73 p += BUFSIZ - sizeof(fp->_ubuf);
74 for (i = sizeof(fp->_ubuf); --i >= 0;)
80 p = realloc(fp->_ub._base, (size_t)(i << 1));
83 /* no overlap (hence can use memcpy) because we doubled the size */
84 (void)memcpy((void *)(p + i), (void *)p, (size_t)i);
87 fp->_ub._size = i << 1;
95 ungetc(int c, FILE *fp)
104 ret = __ungetc(c, fp);
110 * Non-MT-safe version
113 __ungetc(int c, FILE *fp)
117 if ((fp->pub._flags & __SRD) == 0) {
119 * Not already reading: no good unless reading-and-writing.
120 * Otherwise, flush any current write stuff.
122 if ((fp->pub._flags & __SRW) == 0) {
125 if (fp->pub._flags & __SWR) {
129 fp->pub._flags &= ~__SWR;
131 fp->pub._lbfsize = 0;
133 fp->pub._flags |= __SRD;
135 c = (unsigned char)c;
138 * If we are in the middle of ungetc'ing, just continue.
139 * This may require expanding the current ungetc buffer.
142 if (fp->pub._r >= fp->_ub._size && __submore(fp)) {
149 fp->pub._flags &= ~__SEOF;
152 * If we can handle this by simply backing up, do so,
153 * but never replace the original character.
154 * (This makes sscanf() work when scanning `const' data.)
156 if (fp->_bf._base != NULL && fp->pub._p > fp->_bf._base &&
157 fp->pub._p[-1] == c) {
164 * Create an ungetc buffer.
165 * Initially, we will use the `reserve' buffer.
167 fp->_ur = fp->pub._r;
168 fp->_up = fp->pub._p;
169 fp->_ub._base = fp->_ubuf;
170 fp->_ub._size = sizeof(fp->_ubuf);
171 fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
172 fp->pub._p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];