1 /* $OpenBSD: ungetc.c,v 1.9 2005/08/08 08:05:36 espie Exp $ */ 2 /*- 3 * Copyright (c) 1990, 1993 4 * The Regents of the University of California. All rights reserved. 5 * 6 * This code is derived from software contributed to Berkeley by 7 * Chris Torek. 8 * 9 * Redistribution and use in source and binary forms, with or without 10 * modification, are permitted provided that the following conditions 11 * are met: 12 * 1. Redistributions of source code must retain the above copyright 13 * notice, this list of conditions and the following disclaimer. 14 * 2. Redistributions in binary form must reproduce the above copyright 15 * notice, this list of conditions and the following disclaimer in the 16 * documentation and/or other materials provided with the distribution. 17 * 3. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 */ 33 34 #include <stdio.h> 35 #include <stdlib.h> 36 #include <string.h> 37 #include "local.h" 38 39 static int __submore(FILE *); 40 /* 41 * Expand the ungetc buffer `in place'. That is, adjust fp->_p when 42 * the buffer moves, so that it points the same distance from the end, 43 * and move the bytes in the buffer around as necessary so that they 44 * are all at the end (stack-style). 45 */ 46 static int __submore(FILE * fp)47 __submore(FILE *fp) 48 { 49 int i; 50 unsigned char *p; 51 52 if (_UB(fp)._base == fp->_ubuf) { 53 /* 54 * Get a new buffer (rather than expanding the old one). 55 */ 56 if ((p = malloc((size_t)BUFSIZ)) == NULL) 57 return (EOF); 58 _UB(fp)._base = p; 59 _UB(fp)._size = BUFSIZ; 60 p += BUFSIZ - sizeof(fp->_ubuf); 61 for (i = sizeof(fp->_ubuf); --i >= 0;) 62 p[i] = fp->_ubuf[i]; 63 fp->_p = p; 64 return (0); 65 } 66 i = _UB(fp)._size; 67 p = realloc(_UB(fp)._base, i << 1); 68 if (p == NULL) 69 return (EOF); 70 /* no overlap (hence can use memcpy) because we doubled the size */ 71 (void)memcpy((void *)(p + i), (void *)p, (size_t)i); 72 fp->_p = p + i; 73 _UB(fp)._base = p; 74 _UB(fp)._size = i << 1; 75 return (0); 76 } 77 78 int ungetc(int c,FILE * fp)79 ungetc(int c, FILE *fp) 80 { 81 if (c == EOF) 82 return (EOF); 83 if (!__sdidinit) 84 __sinit(); 85 _SET_ORIENTATION(fp, -1); 86 if ((fp->_flags & __SRD) == 0) { 87 /* 88 * Not already reading: no good unless reading-and-writing. 89 * Otherwise, flush any current write stuff. 90 */ 91 if ((fp->_flags & __SRW) == 0) 92 return (EOF); 93 if (fp->_flags & __SWR) { 94 if (__sflush(fp)) 95 return (EOF); 96 fp->_flags &= ~__SWR; 97 fp->_w = 0; 98 fp->_lbfsize = 0; 99 } 100 fp->_flags |= __SRD; 101 } 102 c = (unsigned char)c; 103 104 /* 105 * If we are in the middle of ungetc'ing, just continue. 106 * This may require expanding the current ungetc buffer. 107 */ 108 if (HASUB(fp)) { 109 if (fp->_r >= _UB(fp)._size && __submore(fp)) 110 return (EOF); 111 *--fp->_p = c; 112 fp->_r++; 113 return (c); 114 } 115 fp->_flags &= ~__SEOF; 116 117 /* 118 * If we can handle this by simply backing up, do so, 119 * but never replace the original character. 120 * (This makes sscanf() work when scanning `const' data.) 121 */ 122 if (fp->_bf._base != NULL && fp->_p > fp->_bf._base && 123 fp->_p[-1] == c) { 124 fp->_p--; 125 fp->_r++; 126 return (c); 127 } 128 129 /* 130 * Create an ungetc buffer. 131 * Initially, we will use the `reserve' buffer. 132 */ 133 fp->_ur = fp->_r; 134 fp->_up = fp->_p; 135 _UB(fp)._base = fp->_ubuf; 136 _UB(fp)._size = sizeof(fp->_ubuf); 137 fp->_ubuf[sizeof(fp->_ubuf) - 1] = c; 138 fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1]; 139 fp->_r = 1; 140 return (c); 141 } 142