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 1.6 2004/09/28 18:12:44 otto 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(FILE *fp) 51 { 52 int i; 53 unsigned char *p; 54 55 if (fp->_ub._base == fp->_ubuf) { 56 /* 57 * Get a new buffer (rather than expanding the old one). 58 */ 59 if ((p = malloc((size_t)BUFSIZ)) == NULL) 60 return (EOF); 61 fp->_ub._base = p; 62 fp->_ub._size = BUFSIZ; 63 p += BUFSIZ - sizeof(fp->_ubuf); 64 for (i = sizeof(fp->_ubuf); --i >= 0;) 65 p[i] = fp->_ubuf[i]; 66 fp->_p = p; 67 return (0); 68 } 69 i = fp->_ub._size; 70 p = realloc(fp->_ub._base, i << 1); 71 if (p == NULL) 72 return (EOF); 73 /* no overlap (hence can use memcpy) because we doubled the size */ 74 (void)memcpy((void *)(p + i), (void *)p, (size_t)i); 75 fp->_p = p + i; 76 fp->_ub._base = p; 77 fp->_ub._size = i << 1; 78 return (0); 79 } 80 81 int 82 ungetc(int c, FILE *fp) 83 { 84 if (c == EOF) 85 return (EOF); 86 if (!__sdidinit) 87 __sinit(); 88 if ((fp->_flags & __SRD) == 0) { 89 /* 90 * Not already reading: no good unless reading-and-writing. 91 * Otherwise, flush any current write stuff. 92 */ 93 if ((fp->_flags & __SRW) == 0) 94 return (EOF); 95 if (fp->_flags & __SWR) { 96 if (__sflush(fp)) 97 return (EOF); 98 fp->_flags &= ~__SWR; 99 fp->_w = 0; 100 fp->_lbfsize = 0; 101 } 102 fp->_flags |= __SRD; 103 } 104 c = (unsigned char)c; 105 106 /* 107 * If we are in the middle of ungetc'ing, just continue. 108 * This may require expanding the current ungetc buffer. 109 */ 110 if (HASUB(fp)) { 111 if (fp->_r >= fp->_ub._size && __submore(fp)) 112 return (EOF); 113 *--fp->_p = c; 114 fp->_r++; 115 return (c); 116 } 117 fp->_flags &= ~__SEOF; 118 119 /* 120 * If we can handle this by simply backing up, do so, 121 * but never replace the original character. 122 * (This makes sscanf() work when scanning `const' data.) 123 */ 124 if (fp->_bf._base != NULL && fp->_p > fp->_bf._base && 125 fp->_p[-1] == c) { 126 fp->_p--; 127 fp->_r++; 128 return (c); 129 } 130 131 /* 132 * Create an ungetc buffer. 133 * Initially, we will use the `reserve' buffer. 134 */ 135 fp->_ur = fp->_r; 136 fp->_up = fp->_p; 137 fp->_ub._base = fp->_ubuf; 138 fp->_ub._size = sizeof(fp->_ubuf); 139 fp->_ubuf[sizeof(fp->_ubuf) - 1] = c; 140 fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1]; 141 fp->_r = 1; 142 return (c); 143 } 144