1 /* $NetBSD: ungetc.c,v 1.4 1995/02/02 02:10:47 jtc 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 #if defined(LIBC_SCCS) && !defined(lint) 40 #if 0 41 static char sccsid[] = "@(#)ungetc.c 8.2 (Berkeley) 11/3/93"; 42 #endif 43 static char rcsid[] = "$NetBSD: ungetc.c,v 1.4 1995/02/02 02:10:47 jtc Exp $"; 44 #endif /* LIBC_SCCS and not lint */ 45 46 #include <stdio.h> 47 #include <stdlib.h> 48 #include <string.h> 49 #include "local.h" 50 51 /* 52 * Expand the ungetc buffer `in place'. That is, adjust fp->_p when 53 * the buffer moves, so that it points the same distance from the end, 54 * and move the bytes in the buffer around as necessary so that they 55 * are all at the end (stack-style). 56 */ 57 static 58 __submore(fp) 59 register FILE *fp; 60 { 61 register int i; 62 register unsigned char *p; 63 64 if (fp->_ub._base == fp->_ubuf) { 65 /* 66 * Get a new buffer (rather than expanding the old one). 67 */ 68 if ((p = malloc((size_t)BUFSIZ)) == NULL) 69 return (EOF); 70 fp->_ub._base = p; 71 fp->_ub._size = BUFSIZ; 72 p += BUFSIZ - sizeof(fp->_ubuf); 73 for (i = sizeof(fp->_ubuf); --i >= 0;) 74 p[i] = fp->_ubuf[i]; 75 fp->_p = p; 76 return (0); 77 } 78 i = fp->_ub._size; 79 p = realloc(fp->_ub._base, i << 1); 80 if (p == NULL) 81 return (EOF); 82 /* no overlap (hence can use memcpy) because we doubled the size */ 83 (void)memcpy((void *)(p + i), (void *)p, (size_t)i); 84 fp->_p = p + i; 85 fp->_ub._base = p; 86 fp->_ub._size = i << 1; 87 return (0); 88 } 89 90 ungetc(c, fp) 91 int c; 92 register FILE *fp; 93 { 94 if (c == EOF) 95 return (EOF); 96 if (!__sdidinit) 97 __sinit(); 98 if ((fp->_flags & __SRD) == 0) { 99 /* 100 * Not already reading: no good unless reading-and-writing. 101 * Otherwise, flush any current write stuff. 102 */ 103 if ((fp->_flags & __SRW) == 0) 104 return (EOF); 105 if (fp->_flags & __SWR) { 106 if (__sflush(fp)) 107 return (EOF); 108 fp->_flags &= ~__SWR; 109 fp->_w = 0; 110 fp->_lbfsize = 0; 111 } 112 fp->_flags |= __SRD; 113 } 114 c = (unsigned char)c; 115 116 /* 117 * If we are in the middle of ungetc'ing, just continue. 118 * This may require expanding the current ungetc buffer. 119 */ 120 if (HASUB(fp)) { 121 if (fp->_r >= fp->_ub._size && __submore(fp)) 122 return (EOF); 123 *--fp->_p = c; 124 fp->_r++; 125 return (c); 126 } 127 fp->_flags &= ~__SEOF; 128 129 /* 130 * If we can handle this by simply backing up, do so, 131 * but never replace the original character. 132 * (This makes sscanf() work when scanning `const' data.) 133 */ 134 if (fp->_bf._base != NULL && fp->_p > fp->_bf._base && 135 fp->_p[-1] == c) { 136 fp->_p--; 137 fp->_r++; 138 return (c); 139 } 140 141 /* 142 * Create an ungetc buffer. 143 * Initially, we will use the `reserve' buffer. 144 */ 145 fp->_ur = fp->_r; 146 fp->_up = fp->_p; 147 fp->_ub._base = fp->_ubuf; 148 fp->_ub._size = sizeof(fp->_ubuf); 149 fp->_ubuf[sizeof(fp->_ubuf) - 1] = c; 150 fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1]; 151 fp->_r = 1; 152 return (c); 153 } 154