lib/libc/stdio/ungetc.c

   1 /*-
   2  * Copyright (c) 1990, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * This code is derived from software contributed to Berkeley by
   6  * Chris Torek.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 3. Neither the name of the University nor the names of its contributors
  17  *    may be used to endorse or promote products derived from this software
  18  *    without specific prior written permission.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  *
  32  * @(#)ungetc.c 8.2 (Berkeley) 11/3/93
  33  * $FreeBSD: src/lib/libc/stdio/ungetc.c,v 1.18 2008/04/17 22:17:54 jhb Exp $
  34  */
  35
  36 #include "namespace.h"
  37 #include <stdio.h>
  38 #include <stdlib.h>
  39 #include <string.h>
  40 #include "un-namespace.h"
  41 #include "local.h"
  42 #include "libc_private.h"
  43
  44 static int __submore(FILE *);
  45
  46 /*
  47  * Expand the ungetc buffer `in place'.  That is, adjust fp->pub._p when
  48  * the buffer moves, so that it points the same distance from the end,
  49  * and move the bytes in the buffer around as necessary so that they
  50  * are all at the end (stack-style).
  51  */
  52 static int
  53 __submore(FILE *fp)
  54 {
  55         int i;
  56         unsigned char *p;
  57
  58         if (fp->_ub._base == fp->_ubuf) {
  59                 /*
  60                  * Get a new buffer (rather than expanding the old one).
  61                  */
  62                 if ((p = malloc((size_t)BUFSIZ)) == NULL)
  63                         return (EOF);
  64                 fp->_ub._base = p;
  65                 fp->_ub._size = BUFSIZ;
  66                 p += BUFSIZ - sizeof(fp->_ubuf);
  67                 for (i = sizeof(fp->_ubuf); --i >= 0;)
  68                         p[i] = fp->_ubuf[i];
  69                 fp->pub._p = p;
  70                 return (0);
  71         }
  72         i = fp->_ub._size;
  73         p = realloc(fp->_ub._base, (size_t)(i << 1));
  74         if (p == NULL)
  75                 return (EOF);
  76         /* no overlap (hence can use memcpy) because we doubled the size */
  77         memcpy((void *)(p + i), (void *)p, (size_t)i);
  78         fp->pub._p = p + i;
  79         fp->_ub._base = p;
  80         fp->_ub._size = i << 1;
  81         return (0);
  82 }
  83
  84 /*
  85  * MT-safe version
  86  */
  87 int
  88 ungetc(int c, FILE *fp)
  89 {
  90         int ret;
  91
  92         if (!__sdidinit)
  93                 __sinit();
  94         FLOCKFILE(fp);
  95         ORIENT(fp, -1);
  96         ret = __ungetc(c, fp);
  97         FUNLOCKFILE(fp);
  98         return (ret);
  99 }
 100
 101 /*
 102  * Non-MT-safe version
 103  */
 104 int
 105 __ungetc(int c, FILE *fp)
 106 {
 107         if (c == EOF)
 108                 return (EOF);
 109         if ((fp->pub._flags & __SRD) == 0) {
 110                 /*
 111                  * Not already reading: no good unless reading-and-writing.
 112                  * Otherwise, flush any current write stuff.
 113                  */
 114                 if ((fp->pub._flags & __SRW) == 0)
 115                         return (EOF);
 116                 if (fp->pub._flags & __SWR) {
 117                         if (__sflush(fp))
 118                                 return (EOF);
 119                         fp->pub._flags &= ~__SWR;
 120                         fp->pub._w = 0;
 121                         fp->pub._lbfsize = 0;
 122                 }
 123                 fp->pub._flags |= __SRD;
 124         }
 125         c = (unsigned char)c;
 126
 127         /*
 128          * If we are in the middle of ungetc'ing, just continue.
 129          * This may require expanding the current ungetc buffer.
 130          */
 131         if (HASUB(fp)) {
 132                 if (fp->pub._r >= fp->_ub._size && __submore(fp))
 133                         return (EOF);
 134                 *--fp->pub._p = c;
 135                 fp->pub._r++;
 136                 return (c);
 137         }
 138         fp->pub._flags &= ~__SEOF;
 139
 140         /*
 141          * If we can handle this by simply backing up, do so,
 142          * but never replace the original character.
 143          * (This makes sscanf() work when scanning `const' data.)
 144          */
 145         if (fp->_bf._base != NULL && fp->pub._p > fp->_bf._base &&
 146             fp->pub._p[-1] == c) {
 147                 fp->pub._p--;
 148                 fp->pub._r++;
 149                 return (c);
 150         }
 151
 152         /*
 153          * Create an ungetc buffer.
 154          * Initially, we will use the `reserve' buffer.
 155          */
 156         fp->_ur = fp->pub._r;
 157         fp->_up = fp->pub._p;
 158         fp->_ub._base = fp->_ubuf;
 159         fp->_ub._size = sizeof(fp->_ubuf);
 160         fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
 161         fp->pub._p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
 162         fp->pub._r = 1;
 163         return (c);
 164 }