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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 1.4 2005/01/31 22:29:40 dillon Exp $
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 = realloc(fp->_ub._base, (size_t)(i << 1));
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 << 1;
93 ungetc(int c, FILE *fp)
102 ret = __ungetc(c, fp);
108 * Non-MT-safe version
111 __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) {
123 if (fp->_flags & __SWR) {
127 fp->_flags &= ~__SWR;
133 c = (unsigned char)c;
136 * If we are in the middle of ungetc'ing, just continue.
137 * This may require expanding the current ungetc buffer.
140 if (fp->_r >= fp->_ub._size && __submore(fp)) {
147 fp->_flags &= ~__SEOF;
150 * If we can handle this by simply backing up, do so,
151 * but never replace the original character.
152 * (This makes sscanf() work when scanning `const' data.)
154 if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
162 * Create an ungetc buffer.
163 * Initially, we will use the `reserve' buffer.
167 fp->_ub._base = fp->_ubuf;
168 fp->_ub._size = sizeof(fp->_ubuf);
169 fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
170 fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];