stdio/ungetc.c

   1 /*
   2  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
   7  *
   8  * This file contains Original Code and/or Modifications of Original Code
   9  * as defined in and that are subject to the Apple Public Source License
  10  * Version 2.0 (the 'License'). You may not use this file except in
  11  * compliance with the License. Please obtain a copy of the License at
  12  * http://www.opensource.apple.com/apsl/ and read it before using this
  13  * file.
  14  *
  15  * The Original Code and all software distributed under the License are
  16  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  17  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  18  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  20  * Please see the License for the specific language governing rights and
  21  * limitations under the License.
  22  *
  23  * @APPLE_LICENSE_HEADER_END@
  24  */
  25 /*
  26  * Copyright (c) 1990, 1993
  27  *      The Regents of the University of California.  All rights reserved.
  28  *
  29  * This code is derived from software contributed to Berkeley by
  30  * Chris Torek.
  31  *
  32  * Redistribution and use in source and binary forms, with or without
  33  * modification, are permitted provided that the following conditions
  34  * are met:
  35  * 1. Redistributions of source code must retain the above copyright
  36  *    notice, this list of conditions and the following disclaimer.
  37  * 2. Redistributions in binary form must reproduce the above copyright
  38  *    notice, this list of conditions and the following disclaimer in the
  39  *    documentation and/or other materials provided with the distribution.
  40  * 3. All advertising materials mentioning features or use of this software
  41  *    must display the following acknowledgement:
  42  *      This product includes software developed by the University of
  43  *      California, Berkeley and its contributors.
  44  * 4. Neither the name of the University nor the names of its contributors
  45  *    may be used to endorse or promote products derived from this software
  46  *    without specific prior written permission.
  47  *
  48  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  49  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  50  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  51  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  52  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  53  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  54  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  55  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  56  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  57  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  58  * SUCH DAMAGE.
  59  */
  60
  61
  62 #include <stdio.h>
  63 #include <stdlib.h>
  64 #include <string.h>
  65 #include "local.h"
  66
  67 /*
  68  * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
  69  * the buffer moves, so that it points the same distance from the end,
  70  * and move the bytes in the buffer around as necessary so that they
  71  * are all at the end (stack-style).
  72  */
  73 static int
  74 __submore(fp)
  75         register FILE *fp;
  76 {
  77         register int i;
  78         register unsigned char *p;
  79
  80         if (fp->_ub._base == fp->_ubuf) {
  81                 /*
  82                  * Get a new buffer (rather than expanding the old one).
  83                  */
  84                 if ((p = malloc((size_t)BUFSIZ)) == NULL)
  85                         return (EOF);
  86                 fp->_ub._base = p;
  87                 fp->_ub._size = BUFSIZ;
  88                 p += BUFSIZ - sizeof(fp->_ubuf);
  89                 for (i = sizeof(fp->_ubuf); --i >= 0;)
  90                         p[i] = fp->_ubuf[i];
  91                 fp->_p = p;
  92                 return (0);
  93         }
  94         i = fp->_ub._size;
  95         p = realloc(fp->_ub._base, i << 1);
  96         if (p == NULL)
  97                 return (EOF);
  98         /* no overlap (hence can use memcpy) because we doubled the size */
  99         (void)memcpy((void *)(p + i), (void *)p, (size_t)i);
 100         fp->_p = p + i;
 101         fp->_ub._base = p;
 102         fp->_ub._size = i << 1;
 103         return (0);
 104 }
 105
 106 int
 107 ungetc(c, fp)
 108         int c;
 109         register FILE *fp;
 110 {
 111         if (c == EOF)
 112                 return (EOF);
 113         if (!__sdidinit)
 114                 __sinit();
 115         if ((fp->_flags & __SRD) == 0) {
 116                 /*
 117                  * Not already reading: no good unless reading-and-writing.
 118                  * Otherwise, flush any current write stuff.
 119                  */
 120                 if ((fp->_flags & __SRW) == 0)
 121                         return (EOF);
 122                 if (fp->_flags & __SWR) {
 123                         if (__sflush(fp))
 124                                 return (EOF);
 125                         fp->_flags &= ~__SWR;
 126                         fp->_w = 0;
 127                         fp->_lbfsize = 0;
 128                 }
 129                 fp->_flags |= __SRD;
 130         }
 131         c = (unsigned char)c;
 132
 133         /*
 134          * If we are in the middle of ungetc'ing, just continue.
 135          * This may require expanding the current ungetc buffer.
 136          */
 137         if (HASUB(fp)) {
 138                 if (fp->_r >= fp->_ub._size && __submore(fp))
 139                         return (EOF);
 140                 *--fp->_p = c;
 141                 fp->_r++;
 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                 return (c);
 156         }
 157
 158         /*
 159          * Create an ungetc buffer.
 160          * Initially, we will use the `reserve' buffer.
 161          */
 162         fp->_ur = fp->_r;
 163         fp->_up = fp->_p;
 164         fp->_ub._base = fp->_ubuf;
 165         fp->_ub._size = sizeof(fp->_ubuf);
 166         fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
 167         fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
 168         fp->_r = 1;
 169         return (c);
 170 }