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. All advertising materials mentioning features or use of this software
  17  *    must display the following acknowledgement:
  18  *      This product includes software developed by the University of
  19  *      California, Berkeley and its contributors.
  20  * 4. Neither the name of the University nor the names of its contributors
  21  *    may be used to endorse or promote products derived from this software
  22  *    without specific prior written permission.
  23  *
  24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  34  * SUCH DAMAGE.
  35  *
  36  * @(#)ungetc.c 8.2 (Berkeley) 11/3/93
  37  * $FreeBSD: src/lib/libc/stdio/ungetc.c,v 1.7.2.1 2001/03/05 11:27:49 obrien Exp $
  38  * $DragonFly: src/lib/libc/stdio/ungetc.c,v 1.8 2005/11/20 11:07:30 swildner Exp $
  39  */
  40
  41 #include "namespace.h"
  42 #include <stdio.h>
  43 #include <stdlib.h>
  44 #include <string.h>
  45 #include "un-namespace.h"
  46
  47 #include "local.h"
  48 #include "libc_private.h"
  49 #include "priv_stdio.h"
  50
  51 static int __submore (FILE *);
  52
  53 /*
  54  * Expand the ungetc buffer `in place'.  That is, adjust fp->_p when
  55  * the buffer moves, so that it points the same distance from the end,
  56  * and move the bytes in the buffer around as necessary so that they
  57  * are all at the end (stack-style).
  58  */
  59 static int
  60 __submore(FILE *fp)
  61 {
  62         int i;
  63         unsigned char *p;
  64
  65         if (fp->_ub._base == fp->_ubuf) {
  66                 /*
  67                  * Get a new buffer (rather than expanding the old one).
  68                  */
  69                 if ((p = malloc((size_t)BUFSIZ)) == NULL)
  70                         return (EOF);
  71                 fp->_ub._base = p;
  72                 fp->_ub._size = BUFSIZ;
  73                 p += BUFSIZ - sizeof(fp->_ubuf);
  74                 for (i = sizeof(fp->_ubuf); --i >= 0;)
  75                         p[i] = fp->_ubuf[i];
  76                 fp->pub._p = p;
  77                 return (0);
  78         }
  79         i = fp->_ub._size;
  80         p = realloc(fp->_ub._base, (size_t)(i << 1));
  81         if (p == NULL)
  82                 return (EOF);
  83         /* no overlap (hence can use memcpy) because we doubled the size */
  84         memcpy((void *)(p + i), (void *)p, (size_t)i);
  85         fp->pub._p = p + i;
  86         fp->_ub._base = p;
  87         fp->_ub._size = i << 1;
  88         return (0);
  89 }
  90
  91 /*
  92  * MT-safe version
  93  */
  94 int
  95 ungetc(int c, FILE *fp)
  96 {
  97         int ret;
  98
  99         if (c == EOF)
 100                 return (EOF);
 101         if (!__sdidinit)
 102                 __sinit();
 103         FLOCKFILE(fp);
 104         ret = __ungetc(c, fp);
 105         FUNLOCKFILE(fp);
 106         return(ret);
 107 }
 108
 109 /*
 110  * Non-MT-safe version
 111  */
 112 int
 113 __ungetc(int c, FILE *fp)
 114 {
 115         if (c == EOF)
 116                 return(EOF);
 117         if ((fp->pub._flags & __SRD) == 0) {
 118                 /*
 119                  * Not already reading: no good unless reading-and-writing.
 120                  * Otherwise, flush any current write stuff.
 121                  */
 122                 if ((fp->pub._flags & __SRW) == 0) {
 123                         return (EOF);
 124                 }
 125                 if (fp->pub._flags & __SWR) {
 126                         if (__sflush(fp)) {
 127                                 return (EOF);
 128                         }
 129                         fp->pub._flags &= ~__SWR;
 130                         fp->pub._w = 0;
 131                         fp->pub._lbfsize = 0;
 132                 }
 133                 fp->pub._flags |= __SRD;
 134         }
 135         c = (unsigned char)c;
 136
 137         /*
 138          * If we are in the middle of ungetc'ing, just continue.
 139          * This may require expanding the current ungetc buffer.
 140          */
 141         if (HASUB(fp)) {
 142                 if (fp->pub._r >= fp->_ub._size && __submore(fp)) {
 143                         return (EOF);
 144                 }
 145                 *--fp->pub._p = c;
 146                 fp->pub._r++;
 147                 return (c);
 148         }
 149         fp->pub._flags &= ~__SEOF;
 150
 151         /*
 152          * If we can handle this by simply backing up, do so,
 153          * but never replace the original character.
 154          * (This makes sscanf() work when scanning `const' data.)
 155          */
 156         if (fp->_bf._base != NULL && fp->pub._p > fp->_bf._base &&
 157             fp->pub._p[-1] == c) {
 158                 fp->pub._p--;
 159                 fp->pub._r++;
 160                 return (c);
 161         }
 162
 163         /*
 164          * Create an ungetc buffer.
 165          * Initially, we will use the `reserve' buffer.
 166          */
 167         fp->_ur = fp->pub._r;
 168         fp->_up = fp->pub._p;
 169         fp->_ub._base = fp->_ubuf;
 170         fp->_ub._size = sizeof(fp->_ubuf);
 171         fp->_ubuf[sizeof(fp->_ubuf) - 1] = c;
 172         fp->pub._p = &fp->_ubuf[sizeof(fp->_ubuf) - 1];
 173         fp->pub._r = 1;
 174         return (c);
 175 }