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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 1.3 2003/11/12 20:21:25 eirikn Exp $
45 #include "libc_private.h"
47 static int __submore (FILE *);
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).
61 if (fp->_ub._base == fp->_ubuf) {
63 * Get a new buffer (rather than expanding the old one).
65 if ((p = malloc((size_t)BUFSIZ)) == NULL)
68 fp->_ub._size = BUFSIZ;
69 p += BUFSIZ - sizeof(fp->_ubuf);
70 for (i = sizeof(fp->_ubuf); --i >= 0;)
76 p = realloc(fp->_ub._base, (size_t)(i << 1));
79 /* no overlap (hence can use memcpy) because we doubled the size */
80 (void)memcpy((void *)(p + i), (void *)p, (size_t)i);
83 fp->_ub._size = i << 1;
88 ungetc(int c, FILE *fp)
95 if ((fp->_flags & __SRD) == 0) {
97 * Not already reading: no good unless reading-and-writing.
98 * Otherwise, flush any current write stuff.
100 if ((fp->_flags & __SRW) == 0) {
104 if (fp->_flags & __SWR) {
109 fp->_flags &= ~__SWR;
115 c = (unsigned char)c;
118 * If we are in the middle of ungetc'ing, just continue.
119 * This may require expanding the current ungetc buffer.
122 if (fp->_r >= fp->_ub._size && __submore(fp)) {
131 fp->_flags &= ~__SEOF;
134 * If we can handle this by simply backing up, do so,
135 * but never replace the original character.
136 * (This makes sscanf() work when scanning `const' data.)
138 if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
147 * Create an ungetc buffer.
148 * Initially, we will use the `reserve' buffer.
152 fp->_ub._base = fp->_ubuf;
153 fp->_ub._size = sizeof(fp->_ubuf);
154 fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
155 fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];