lib/libc/stdio/ungetc.c

   1 /*      $NetBSD: ungetc.c,v 1.14 2003/08/07 16:43:34 agc Exp $  */
   2
   3 /*-
   4  * Copyright (c) 1990, 1993
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * This code is derived from software contributed to Berkeley by
   8  * Chris Torek.
   9  *
  10  * Redistribution and use in source and binary forms, with or without
  11  * modification, are permitted provided that the following conditions
  12  * are met:
  13  * 1. Redistributions of source code must retain the above copyright
  14  *    notice, this list of conditions and the following disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  * 3. Neither the name of the University nor the names of its contributors
  19  *    may be used to endorse or promote products derived from this software
  20  *    without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  */
  34
  35 #include <sys/cdefs.h>
  36 #if defined(LIBC_SCCS) && !defined(lint)
  37 #if 0
  38 static char sccsid[] = "@(#)ungetc.c    8.2 (Berkeley) 11/3/93";
  39 #else
  40 __RCSID("$NetBSD: ungetc.c,v 1.14 2003/08/07 16:43:34 agc Exp $");
  41 #endif
  42 #endif /* LIBC_SCCS and not lint */
  43
  44 #include <assert.h>
  45 #include <errno.h>
  46 #include <stdio.h>
  47 #include <stdlib.h>
  48 #include <string.h>
  49 #include "reentrant.h"
  50 #include "local.h"
  51
  52 static int __submore __P((FILE *));
  53 /*
  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).
  58  */
  59 static int
  60 __submore(fp)
  61         FILE *fp;
  62 {
  63         int i;
  64         unsigned char *p;
  65
  66         _DIAGASSERT(fp != NULL);
  67
  68         if (_UB(fp)._base == fp->_ubuf) {
  69                 /*
  70                  * Get a new buffer (rather than expanding the old one).
  71                  */
  72                 if ((p = malloc((size_t)BUFSIZ)) == NULL)
  73                         return (EOF);
  74                 _UB(fp)._base = p;
  75                 _UB(fp)._size = BUFSIZ;
  76                 p += BUFSIZ - sizeof(fp->_ubuf);
  77                 for (i = sizeof(fp->_ubuf); --i >= 0;)
  78                         p[i] = fp->_ubuf[i];
  79                 fp->_p = p;
  80                 return (0);
  81         }
  82         i = _UB(fp)._size;
  83         p = realloc(_UB(fp)._base, (size_t)(i << 1));
  84         if (p == NULL)
  85                 return (EOF);
  86         /* no overlap (hence can use memcpy) because we doubled the size */
  87         (void)memcpy((p + i), p, (size_t)i);
  88         fp->_p = p + i;
  89         _UB(fp)._base = p;
  90         _UB(fp)._size = i << 1;
  91         return (0);
  92 }
  93
  94 int
  95 ungetc(c, fp)
  96         int c;
  97         FILE *fp;
  98 {
  99
 100         _DIAGASSERT(fp != NULL);
 101
 102         if (c == EOF)
 103                 return (EOF);
 104         if (!__sdidinit)
 105                 __sinit();
 106         FLOCKFILE(fp);
 107         _SET_ORIENTATION(fp, -1);
 108         if ((fp->_flags & __SRD) == 0) {
 109                 /*
 110                  * Not already reading: no good unless reading-and-writing.
 111                  * Otherwise, flush any current write stuff.
 112                  */
 113                 if ((fp->_flags & __SRW) == 0) {
 114                         FUNLOCKFILE(fp);
 115                         return (EOF);
 116                 }
 117                 if (fp->_flags & __SWR) {
 118                         if (__sflush(fp)) {
 119                                 FUNLOCKFILE(fp);
 120                                 return (EOF);
 121                         }
 122                         fp->_flags &= ~__SWR;
 123                         fp->_w = 0;
 124                         fp->_lbfsize = 0;
 125                 }
 126                 fp->_flags |= __SRD;
 127         }
 128         c = (unsigned char)c;
 129
 130         /*
 131          * If we are in the middle of ungetc'ing, just continue.
 132          * This may require expanding the current ungetc buffer.
 133          */
 134         if (HASUB(fp)) {
 135                 if (fp->_r >= _UB(fp)._size && __submore(fp)) {
 136                         FUNLOCKFILE(fp);
 137                         return (EOF);
 138                 }
 139                 *--fp->_p = c;
 140                 fp->_r++;
 141                 FUNLOCKFILE(fp);
 142                 return (c);
 143         }
 144         fp->_flags &= ~__SEOF;
 145
 146         /*
 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.)
 150          */
 151         if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
 152             fp->_p[-1] == c) {
 153                 fp->_p--;
 154                 fp->_r++;
 155                 FUNLOCKFILE(fp);
 156                 return (c);
 157         }
 158
 159         /*
 160          * Create an ungetc buffer.
 161          * Initially, we will use the `reserve' buffer.
 162          */
 163         fp->_ur = fp->_r;
 164         fp->_up = fp->_p;
 165         _UB(fp)._base = fp->_ubuf;
 166         _UB(fp)._size = sizeof(fp->_ubuf);
 167         fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
 168         fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
 169         fp->_r = 1;
 170         FUNLOCKFILE(fp);
 171         return (c);
 172 }