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 33 #if defined(LIBC_SCCS) && !defined(lint) 34 static char rcsid[] = "$OpenBSD: ungetc.c,v 1.5 2003/06/02 20:18:37 millert Exp $"; 35 #endif /* LIBC_SCCS and not lint */ 36 37 #include <stdio.h> 38 #include <stdlib.h> 39 #include <string.h> 40 #include "local.h" 41 42 static int __submore(FILE *); 43 /* 44 * Expand the ungetc buffer `in place'. That is, adjust fp->_p when 45 * the buffer moves, so that it points the same distance from the end, 46 * and move the bytes in the buffer around as necessary so that they 47 * are all at the end (stack-style). 48 */ 49 static int 50 __submore(fp) 51 FILE *fp; 52 { 53 register int i; 54 register unsigned char *p; 55 56 if (fp->_ub._base == fp->_ubuf) { 57 /* 58 * Get a new buffer (rather than expanding the old one). 59 */ 60 if ((p = malloc((size_t)BUFSIZ)) == NULL) 61 return (EOF); 62 fp->_ub._base = p; 63 fp->_ub._size = BUFSIZ; 64 p += BUFSIZ - sizeof(fp->_ubuf); 65 for (i = sizeof(fp->_ubuf); --i >= 0;) 66 p[i] = fp->_ubuf[i]; 67 fp->_p = p; 68 return (0); 69 } 70 i = fp->_ub._size; 71 p = realloc(fp->_ub._base, i << 1); 72 if (p == NULL) 73 return (EOF); 74 /* no overlap (hence can use memcpy) because we doubled the size */ 75 (void)memcpy((void *)(p + i), (void *)p, (size_t)i); 76 fp->_p = p + i; 77 fp->_ub._base = p; 78 fp->_ub._size = i << 1; 79 return (0); 80 } 81 82 int 83 ungetc(c, fp) 84 int c; 85 register FILE *fp; 86 { 87 if (c == EOF) 88 return (EOF); 89 if (!__sdidinit) 90 __sinit(); 91 if ((fp->_flags & __SRD) == 0) { 92 /* 93 * Not already reading: no good unless reading-and-writing. 94 * Otherwise, flush any current write stuff. 95 */ 96 if ((fp->_flags & __SRW) == 0) 97 return (EOF); 98 if (fp->_flags & __SWR) { 99 if (__sflush(fp)) 100 return (EOF); 101 fp->_flags &= ~__SWR; 102 fp->_w = 0; 103 fp->_lbfsize = 0; 104 } 105 fp->_flags |= __SRD; 106 } 107 c = (unsigned char)c; 108 109 /* 110 * If we are in the middle of ungetc'ing, just continue. 111 * This may require expanding the current ungetc buffer. 112 */ 113 if (HASUB(fp)) { 114 if (fp->_r >= fp->_ub._size && __submore(fp)) 115 return (EOF); 116 *--fp->_p = c; 117 fp->_r++; 118 return (c); 119 } 120 fp->_flags &= ~__SEOF; 121 122 /* 123 * If we can handle this by simply backing up, do so, 124 * but never replace the original character. 125 * (This makes sscanf() work when scanning `const' data.) 126 */ 127 if (fp->_bf._base != NULL && fp->_p > fp->_bf._base && 128 fp->_p[-1] == c) { 129 fp->_p--; 130 fp->_r++; 131 return (c); 132 } 133 134 /* 135 * Create an ungetc buffer. 136 * Initially, we will use the `reserve' buffer. 137 */ 138 fp->_ur = fp->_r; 139 fp->_up = fp->_p; 140 fp->_ub._base = fp->_ubuf; 141 fp->_ub._size = sizeof(fp->_ubuf); 142 fp->_ubuf[sizeof(fp->_ubuf) - 1] = c; 143 fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1]; 144 fp->_r = 1; 145 return (c); 146 } 147