lib/libc/stdio/ungetc.c

   1 /*      $NetBSD: ungetc.c,v 1.17 2012/03/15 18:22:30 christos 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 1.17 2012/03/15 18:22:30 christos 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 /*
  53  * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
  54  * the buffer moves, so that it points the same distance from the end,
  55  * and move the bytes in the buffer around as necessary so that they
  56  * are all at the end (stack-style).
  57  */
  58 static int
  59 __submore(FILE *fp)
  60 {
  61         int i;
  62         unsigned char *p;
  63
  64         _DIAGASSERT(fp != NULL);
  65
  66         if (_UB(fp)._base == fp->_ubuf) {
  67                 /*
  68                  * Get a new buffer (rather than expanding the old one).
  69                  */
  70                 if ((p = malloc((size_t)BUFSIZ)) == NULL)
  71                         return EOF;
  72                 _UB(fp)._base = p;
  73                 _UB(fp)._size = BUFSIZ;
  74                 p += BUFSIZ - sizeof(fp->_ubuf);
  75                 for (i = sizeof(fp->_ubuf); --i >= 0;)
  76                         p[i] = fp->_ubuf[i];
  77                 fp->_p = p;
  78                 return 0;
  79         }
  80         i = _UB(fp)._size;
  81         p = realloc(_UB(fp)._base, (size_t)(i << 1));
  82         if (p == NULL)
  83                 return EOF;
  84         /* no overlap (hence can use memcpy) because we doubled the size */
  85         (void)memcpy((p + i), p, (size_t)i);
  86         fp->_p = p + i;
  87         _UB(fp)._base = p;
  88         _UB(fp)._size = i << 1;
  89         return 0;
  90 }
  91
  92 int
  93 ungetc(int c, FILE *fp)
  94 {
  95
  96         _DIAGASSERT(fp != NULL);
  97
  98         if (c == EOF)
  99                 return EOF;
 100         if (!__sdidinit)
 101                 __sinit();
 102         FLOCKFILE(fp);
 103         _SET_ORIENTATION(fp, -1);
 104         if ((fp->_flags & __SRD) == 0) {
 105                 /*
 106                  * Not already reading: no good unless reading-and-writing.
 107                  * Otherwise, flush any current write stuff.
 108                  */
 109                 if ((fp->_flags & __SRW) == 0) {
 110                         FUNLOCKFILE(fp);
 111                         return EOF;
 112                 }
 113                 if (fp->_flags & __SWR) {
 114                         if (__sflush(fp)) {
 115                                 FUNLOCKFILE(fp);
 116                                 return EOF;
 117                         }
 118                         fp->_flags &= ~__SWR;
 119                         fp->_w = 0;
 120                         fp->_lbfsize = 0;
 121                 }
 122                 fp->_flags |= __SRD;
 123         }
 124         c = (unsigned char)c;
 125
 126         /*
 127          * If we are in the middle of ungetc'ing, just continue.
 128          * This may require expanding the current ungetc buffer.
 129          */
 130         if (HASUB(fp)) {
 131                 if (fp->_r >= _UB(fp)._size && __submore(fp)) {
 132                         FUNLOCKFILE(fp);
 133                         return EOF;
 134                 }
 135                 *--fp->_p = c;
 136                 fp->_r++;
 137                 FUNLOCKFILE(fp);
 138                 return c;
 139         }
 140         fp->_flags &= ~__SEOF;
 141
 142         /*
 143          * If we can handle this by simply backing up, do so,
 144          * but never replace the original character.
 145          * (This makes sscanf() work when scanning `const' data.)
 146          */
 147         if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
 148             fp->_p[-1] == c) {
 149                 fp->_p--;
 150                 fp->_r++;
 151                 FUNLOCKFILE(fp);
 152                 return c;
 153         }
 154
 155         /*
 156          * Create an ungetc buffer.
 157          * Initially, we will use the `reserve' buffer.
 158          */
 159         fp->_ur = fp->_r;
 160         fp->_up = fp->_p;
 161         _UB(fp)._base = fp->_ubuf;
 162         _UB(fp)._size = sizeof(fp->_ubuf);
 163         fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
 164         fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
 165         fp->_r = 1;
 166         FUNLOCKFILE(fp);
 167         return c;
 168 }