stdio/ungetc.c

   1 /*
   2  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * The contents of this file constitute Original Code as defined in and
   7  * are subject to the Apple Public Source License Version 1.1 (the
   8  * "License").  You may not use this file except in compliance with the
   9  * License.  Please obtain a copy of the License at
  10  * http://www.apple.com/publicsource and read it before using this file.
  11  *
  12  * This Original Code and all software distributed under the License are
  13  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  14  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  15  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  16  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
  17  * License for the specific language governing rights and limitations
  18  * under the License.
  19  *
  20  * @APPLE_LICENSE_HEADER_END@
  21  */
  22 /*
  23  * Copyright (c) 1990, 1993
  24  *      The Regents of the University of California.  All rights reserved.
  25  *
  26  * This code is derived from software contributed to Berkeley by
  27  * Chris Torek.
  28  *
  29  * Redistribution and use in source and binary forms, with or without
  30  * modification, are permitted provided that the following conditions
  31  * are met:
  32  * 1. Redistributions of source code must retain the above copyright
  33  *    notice, this list of conditions and the following disclaimer.
  34  * 2. Redistributions in binary form must reproduce the above copyright
  35  *    notice, this list of conditions and the following disclaimer in the
  36  *    documentation and/or other materials provided with the distribution.
  37  * 3. All advertising materials mentioning features or use of this software
  38  *    must display the following acknowledgement:
  39  *      This product includes software developed by the University of
  40  *      California, Berkeley and its contributors.
  41  * 4. Neither the name of the University nor the names of its contributors
  42  *    may be used to endorse or promote products derived from this software
  43  *    without specific prior written permission.
  44  *
  45  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  46  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  47  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  48  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  49  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  50  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  51  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  52  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  53  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  54  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  55  * SUCH DAMAGE.
  56  */
  57
  58
  59 #include <stdio.h>
  60 #include <stdlib.h>
  61 #include <string.h>
  62 #include "local.h"
  63
  64 /*
  65  * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
  66  * the buffer moves, so that it points the same distance from the end,
  67  * and move the bytes in the buffer around as necessary so that they
  68  * are all at the end (stack-style).
  69  */
  70 static int
  71 __submore(fp)
  72         register FILE *fp;
  73 {
  74         register int i;
  75         register unsigned char *p;
  76
  77         if (fp->_ub._base == fp->_ubuf) {
  78                 /*
  79                  * Get a new buffer (rather than expanding the old one).
  80                  */
  81                 if ((p = malloc((size_t)BUFSIZ)) == NULL)
  82                         return (EOF);
  83                 fp->_ub._base = p;
  84                 fp->_ub._size = BUFSIZ;
  85                 p += BUFSIZ - sizeof(fp->_ubuf);
  86                 for (i = sizeof(fp->_ubuf); --i >= 0;)
  87                         p[i] = fp->_ubuf[i];
  88                 fp->_p = p;
  89                 return (0);
  90         }
  91         i = fp->_ub._size;
  92         p = realloc(fp->_ub._base, i << 1);
  93         if (p == NULL)
  94                 return (EOF);
  95         /* no overlap (hence can use memcpy) because we doubled the size */
  96         (void)memcpy((void *)(p + i), (void *)p, (size_t)i);
  97         fp->_p = p + i;
  98         fp->_ub._base = p;
  99         fp->_ub._size = i << 1;
 100         return (0);
 101 }
 102
 103 int
 104 ungetc(c, fp)
 105         int c;
 106         register FILE *fp;
 107 {
 108         if (c == EOF)
 109                 return (EOF);
 110         if (!__sdidinit)
 111                 __sinit();
 112         if ((fp->_flags & __SRD) == 0) {
 113                 /*
 114                  * Not already reading: no good unless reading-and-writing.
 115                  * Otherwise, flush any current write stuff.
 116                  */
 117                 if ((fp->_flags & __SRW) == 0)
 118                         return (EOF);
 119                 if (fp->_flags & __SWR) {
 120                         if (__sflush(fp))
 121                                 return (EOF);
 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 >= fp->_ub._size && __submore(fp))
 136                         return (EOF);
 137                 *--fp->_p = c;
 138                 fp->_r++;
 139                 return (c);
 140         }
 141         fp->_flags &= ~__SEOF;
 142
 143         /*
 144          * If we can handle this by simply backing up, do so,
 145          * but never replace the original character.
 146          * (This makes sscanf() work when scanning `const' data.)
 147          */
 148         if (fp->_bf._base != NULL && fp->_p > fp->_bf._base &&
 149             fp->_p[-1] == c) {
 150                 fp->_p--;
 151                 fp->_r++;
 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         fp->_ub._base = fp->_ubuf;
 162         fp->_ub._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         return (c);
 167 }