1 /* $NetBSD: ungetc.c,v 1.6 1997/07/13 20:15:33 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 1.6 1997/07/13 20:15:33 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 53 static int __submore __P((FILE *)); 54 /* 55 * Expand the ungetc buffer `in place'. That is, adjust fp->_p when 56 * the buffer moves, so that it points the same distance from the end, 57 * and move the bytes in the buffer around as necessary so that they 58 * are all at the end (stack-style). 59 */ 60 static int 61 __submore(fp) 62 register FILE *fp; 63 { 64 register int i; 65 register unsigned char *p; 66 67 if (fp->_ub._base == fp->_ubuf) { 68 /* 69 * Get a new buffer (rather than expanding the old one). 70 */ 71 if ((p = malloc((size_t)BUFSIZ)) == NULL) 72 return (EOF); 73 fp->_ub._base = p; 74 fp->_ub._size = BUFSIZ; 75 p += BUFSIZ - sizeof(fp->_ubuf); 76 for (i = sizeof(fp->_ubuf); --i >= 0;) 77 p[i] = fp->_ubuf[i]; 78 fp->_p = p; 79 return (0); 80 } 81 i = fp->_ub._size; 82 p = realloc(fp->_ub._base, i << 1); 83 if (p == NULL) 84 return (EOF); 85 /* no overlap (hence can use memcpy) because we doubled the size */ 86 (void)memcpy((void *)(p + i), (void *)p, (size_t)i); 87 fp->_p = p + i; 88 fp->_ub._base = p; 89 fp->_ub._size = i << 1; 90 return (0); 91 } 92 93 int 94 ungetc(c, fp) 95 int c; 96 register FILE *fp; 97 { 98 if (c == EOF) 99 return (EOF); 100 if (!__sdidinit) 101 __sinit(); 102 if ((fp->_flags & __SRD) == 0) { 103 /* 104 * Not already reading: no good unless reading-and-writing. 105 * Otherwise, flush any current write stuff. 106 */ 107 if ((fp->_flags & __SRW) == 0) 108 return (EOF); 109 if (fp->_flags & __SWR) { 110 if (__sflush(fp)) 111 return (EOF); 112 fp->_flags &= ~__SWR; 113 fp->_w = 0; 114 fp->_lbfsize = 0; 115 } 116 fp->_flags |= __SRD; 117 } 118 c = (unsigned char)c; 119 120 /* 121 * If we are in the middle of ungetc'ing, just continue. 122 * This may require expanding the current ungetc buffer. 123 */ 124 if (HASUB(fp)) { 125 if (fp->_r >= fp->_ub._size && __submore(fp)) 126 return (EOF); 127 *--fp->_p = c; 128 fp->_r++; 129 return (c); 130 } 131 fp->_flags &= ~__SEOF; 132 133 /* 134 * If we can handle this by simply backing up, do so, 135 * but never replace the original character. 136 * (This makes sscanf() work when scanning `const' data.) 137 */ 138 if (fp->_bf._base != NULL && fp->_p > fp->_bf._base && 139 fp->_p[-1] == c) { 140 fp->_p--; 141 fp->_r++; 142 return (c); 143 } 144 145 /* 146 * Create an ungetc buffer. 147 * Initially, we will use the `reserve' buffer. 148 */ 149 fp->_ur = fp->_r; 150 fp->_up = fp->_p; 151 fp->_ub._base = fp->_ubuf; 152 fp->_ub._size = sizeof(fp->_ubuf); 153 fp->_ubuf[sizeof(fp->_ubuf) - 1] = c; 154 fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1]; 155 fp->_r = 1; 156 return (c); 157 } 158