StdLib/LibC/Stdio/ungetc.c

   1 /** @file
   2     Implementation of ungetc as declared in <stdio.h>.
   3
   4     Copyright (c) 2010, Intel Corporation. All rights reserved.<BR>
   5     This program and the accompanying materials are licensed and made available
   6     under the terms and conditions of the BSD License that accompanies this
   7     distribution.  The full text of the license may be found at
   8     http://opensource.org/licenses/bsd-license.php.
   9
  10     THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  11     WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  12
  13     Copyright (c) 1990, 1993
  14     The Regents of the University of California.  All rights reserved.
  15
  16     This code is derived from software contributed to Berkeley by
  17     Chris Torek.
  18
  19     Redistribution and use in source and binary forms, with or without
  20     modification, are permitted provided that the following conditions
  21     are met:
  22       - Redistributions of source code must retain the above copyright
  23         notice, this list of conditions and the following disclaimer.
  24       - Redistributions in binary form must reproduce the above copyright
  25         notice, this list of conditions and the following disclaimer in the
  26         documentation and/or other materials provided with the distribution.
  27       - Neither the name of the University nor the names of its contributors
  28         may be used to endorse or promote products derived from this software
  29         without specific prior written permission.
  30
  31     THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  32     AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  33     IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  34     ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
  35     LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  36     CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  37     SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  38     INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  39     CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  40     ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  41     POSSIBILITY OF SUCH DAMAGE.
  42
  43     NetBSD: ungetc.c,v 1.14 2003/08/07 16:43:34 agc Exp
  44     ungetc.c  8.2 (Berkeley) 11/3/93
  45 **/
  46 #include  <LibConfig.h>
  47
  48 #include <assert.h>
  49 #include <errno.h>
  50 #include <stdio.h>
  51 #include <stdlib.h>
  52 #include <string.h>
  53 #include "reentrant.h"
  54 #include "local.h"
  55
  56 static int __submore(FILE *);
  57 /*
  58  * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
  59  * the buffer moves, so that it points the same distance from the end,
  60  * and move the bytes in the buffer around as necessary so that they
  61  * are all at the end (stack-style).
  62  */
  63 static int
  64 __submore(FILE *fp)
  65 {
  66   int i;
  67   unsigned char *p;
  68
  69   _DIAGASSERT(fp != NULL);
  70
  71   if (_UB(fp)._base == fp->_ubuf) {
  72     /*
  73      * Get a new buffer (rather than expanding the old one).
  74      */
  75     if ((p = malloc((size_t)BUFSIZ)) == NULL)
  76       return (EOF);
  77     _UB(fp)._base = p;
  78     _UB(fp)._size = BUFSIZ;
  79     p += BUFSIZ - sizeof(fp->_ubuf);
  80     for (i = sizeof(fp->_ubuf); --i >= 0;)
  81       p[i] = fp->_ubuf[i];
  82     fp->_p = p;
  83     return (0);
  84   }
  85   i = _UB(fp)._size;
  86   p = realloc(_UB(fp)._base, (size_t)(i << 1));
  87   if (p == NULL)
  88     return (EOF);
  89   /* no overlap (hence can use memcpy) because we doubled the size */
  90   (void)memcpy((void *)(p + i), (void *)p, (size_t)i);
  91   fp->_p = p + i;
  92   _UB(fp)._base = p;
  93   _UB(fp)._size = i << 1;
  94   return (0);
  95 }
  96
  97 int
  98 ungetc(int c, FILE *fp)
  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 = (unsigned char)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] = (unsigned char)c;
 168   fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
 169   fp->_r = 1;
 170   FUNLOCKFILE(fp);
 171   return (c);
 172 }