1 /* $NetBSD: ungetc.c,v 1.9 1998/11/15 17:19:53 christos Exp $ */ 2 3 /*- 4 * Copyright (c) 1990, 1993 5 * The Regents of the University of California. All rights reserved. 6 * 7 * This code is derived from software contributed to Berkeley by 8 * Chris Torek. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the University of 21 * California, Berkeley and its contributors. 22 * 4. Neither the name of the University nor the names of its contributors 23 * may be used to endorse or promote products derived from this software 24 * without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 */ 38 39 #include <sys/cdefs.h> 40 #if defined(LIBC_SCCS) && !defined(lint) 41 #if 0 42 static char sccsid[] = "@(#)ungetc.c 8.2 (Berkeley) 11/3/93"; 43 #else 44 __RCSID("$NetBSD: ungetc.c,v 1.9 1998/11/15 17:19:53 christos Exp $"); 45 #endif 46 #endif /* LIBC_SCCS and not lint */ 47 48 #include <stdio.h> 49 #include <stdlib.h> 50 #include <string.h> 51 #include "local.h" 52 #include "reentrant.h" 53 54 static int __submore __P((FILE *)); 55 /* 56 * Expand the ungetc buffer `in place'. That is, adjust fp->_p when 57 * the buffer moves, so that it points the same distance from the end, 58 * and move the bytes in the buffer around as necessary so that they 59 * are all at the end (stack-style). 60 */ 61 static int 62 __submore(fp) 63 FILE *fp; 64 { 65 int i; 66 unsigned char *p; 67 68 if (fp->_ub._base == fp->_ubuf) { 69 /* 70 * Get a new buffer (rather than expanding the old one). 71 */ 72 if ((p = malloc((size_t)BUFSIZ)) == NULL) 73 return (EOF); 74 fp->_ub._base = p; 75 fp->_ub._size = BUFSIZ; 76 p += BUFSIZ - sizeof(fp->_ubuf); 77 for (i = sizeof(fp->_ubuf); --i >= 0;) 78 p[i] = fp->_ubuf[i]; 79 fp->_p = p; 80 return (0); 81 } 82 i = fp->_ub._size; 83 p = realloc(fp->_ub._base, (size_t)(i << 1)); 84 if (p == NULL) 85 return (EOF); 86 /* no overlap (hence can use memcpy) because we doubled the size */ 87 (void)memcpy((void *)(p + i), (void *)p, (size_t)i); 88 fp->_p = p + i; 89 fp->_ub._base = p; 90 fp->_ub._size = i << 1; 91 return (0); 92 } 93 94 int 95 ungetc(c, fp) 96 int c; 97 FILE *fp; 98 { 99 if (c == EOF) 100 return (EOF); 101 if (!__sdidinit) 102 __sinit(); 103 FLOCKFILE(fp); 104 if ((fp->_flags & __SRD) == 0) { 105 /* 106 * Not already reading: no good unless reading-and-writing. 107 * Otherwise, flush any current write stuff. 108 */ 109 if ((fp->_flags & __SRW) == 0) { 110 FUNLOCKFILE(fp); 111 return (EOF); 112 } 113 if (fp->_flags & __SWR) { 114 if (__sflush(fp)) { 115 FUNLOCKFILE(fp); 116 return (EOF); 117 } 118 fp->_flags &= ~__SWR; 119 fp->_w = 0; 120 fp->_lbfsize = 0; 121 } 122 fp->_flags |= __SRD; 123 } 124 c = (unsigned char)c; 125 126 /* 127 * If we are in the middle of ungetc'ing, just continue. 128 * This may require expanding the current ungetc buffer. 129 */ 130 if (HASUB(fp)) { 131 if (fp->_r >= fp->_ub._size && __submore(fp)) { 132 FUNLOCKFILE(fp); 133 return (EOF); 134 } 135 *--fp->_p = c; 136 fp->_r++; 137 FUNLOCKFILE(fp); 138 return (c); 139 } 140 fp->_flags &= ~__SEOF; 141 142 /* 143 * If we can handle this by simply backing up, do so, 144 * but never replace the original character. 145 * (This makes sscanf() work when scanning `const' data.) 146 */ 147 if (fp->_bf._base != NULL && fp->_p > fp->_bf._base && 148 fp->_p[-1] == c) { 149 fp->_p--; 150 fp->_r++; 151 FUNLOCKFILE(fp); 152 return (c); 153 } 154 155 /* 156 * Create an ungetc buffer. 157 * Initially, we will use the `reserve' buffer. 158 */ 159 fp->_ur = fp->_r; 160 fp->_up = fp->_p; 161 fp->_ub._base = fp->_ubuf; 162 fp->_ub._size = sizeof(fp->_ubuf); 163 fp->_ubuf[sizeof(fp->_ubuf) - 1] = c; 164 fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1]; 165 fp->_r = 1; 166 FUNLOCKFILE(fp); 167 return (c); 168 } 169