ungetc.c (4503B)
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. All advertising materials mentioning features or use of this software 17 * must display the following acknowledgement: 18 * This product includes software developed by the University of 19 * California, Berkeley and its contributors. 20 * 4. Neither the name of the University nor the names of its contributors 21 * may be used to endorse or promote products derived from this software 22 * without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 */ 36 37 #if defined(LIBC_SCCS) && !defined(lint) 38 static char rcsid[] = "$OpenBSD: ungetc.c,v 1.2 1996/08/19 08:33:11 tholo Exp $"; 39 #endif /* LIBC_SCCS and not lint */ 40 41 #include <stdio.h> 42 #include <stdlib.h> 43 #include <string.h> 44 #include "local.h" 45 46 /* 47 * Expand the ungetc buffer `in place'. That is, adjust fp->_p when 48 * the buffer moves, so that it points the same distance from the end, 49 * and move the bytes in the buffer around as necessary so that they 50 * are all at the end (stack-style). 51 */ 52 static int 53 __submore(fp) 54 register FILE *fp; 55 { 56 register int i; 57 register unsigned char *p; 58 59 if (fp->_ub._base == fp->_ubuf) { 60 /* 61 * Get a new buffer (rather than expanding the old one). 62 */ 63 if ((p = malloc((size_t)BUFSIZ)) == NULL) 64 return (EOF); 65 fp->_ub._base = p; 66 fp->_ub._size = BUFSIZ; 67 p += BUFSIZ - sizeof(fp->_ubuf); 68 for (i = sizeof(fp->_ubuf); --i >= 0;) 69 p[i] = fp->_ubuf[i]; 70 fp->_p = p; 71 return (0); 72 } 73 i = fp->_ub._size; 74 p = realloc(fp->_ub._base, i << 1); 75 if (p == NULL) 76 return (EOF); 77 /* no overlap (hence can use memcpy) because we doubled the size */ 78 (void)memcpy((void *)(p + i), (void *)p, (size_t)i); 79 fp->_p = p + i; 80 fp->_ub._base = p; 81 fp->_ub._size = i << 1; 82 return (0); 83 } 84 85 int 86 ungetc(c, fp) 87 int c; 88 register FILE *fp; 89 { 90 if (c == EOF) 91 return (EOF); 92 if (!__sdidinit) 93 __sinit(); 94 if ((fp->_flags & __SRD) == 0) { 95 /* 96 * Not already reading: no good unless reading-and-writing. 97 * Otherwise, flush any current write stuff. 98 */ 99 if ((fp->_flags & __SRW) == 0) 100 return (EOF); 101 if (fp->_flags & __SWR) { 102 if (__sflush(fp)) 103 return (EOF); 104 fp->_flags &= ~__SWR; 105 fp->_w = 0; 106 fp->_lbfsize = 0; 107 } 108 fp->_flags |= __SRD; 109 } 110 c = (unsigned char)c; 111 112 /* 113 * If we are in the middle of ungetc'ing, just continue. 114 * This may require expanding the current ungetc buffer. 115 */ 116 if (HASUB(fp)) { 117 if (fp->_r >= fp->_ub._size && __submore(fp)) 118 return (EOF); 119 *--fp->_p = c; 120 fp->_r++; 121 return (c); 122 } 123 fp->_flags &= ~__SEOF; 124 125 /* 126 * If we can handle this by simply backing up, do so, 127 * but never replace the original character. 128 * (This makes sscanf() work when scanning `const' data.) 129 */ 130 if (fp->_bf._base != NULL && fp->_p > fp->_bf._base && 131 fp->_p[-1] == c) { 132 fp->_p--; 133 fp->_r++; 134 return (c); 135 } 136 137 /* 138 * Create an ungetc buffer. 139 * Initially, we will use the `reserve' buffer. 140 */ 141 fp->_ur = fp->_r; 142 fp->_up = fp->_p; 143 fp->_ub._base = fp->_ubuf; 144 fp->_ub._size = sizeof(fp->_ubuf); 145 fp->_ubuf[sizeof(fp->_ubuf) - 1] = c; 146 fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1]; 147 fp->_r = 1; 148 return (c); 149 }