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 * %sccs.include.redist.c% 9 */ 10 11 #if defined(LIBC_SCCS) && !defined(lint) 12 static char sccsid[] = "@(#)ungetc.c 8.2 (Berkeley) 11/03/93"; 13 #endif /* LIBC_SCCS and not lint */ 14 15 #include <stdio.h> 16 #include <stdlib.h> 17 #include <string.h> 18 #include "local.h" 19 20 /* 21 * Expand the ungetc buffer `in place'. That is, adjust fp->_p when 22 * the buffer moves, so that it points the same distance from the end, 23 * and move the bytes in the buffer around as necessary so that they 24 * are all at the end (stack-style). 25 */ 26 static 27 __submore(fp) 28 register FILE *fp; 29 { 30 register int i; 31 register unsigned char *p; 32 33 if (fp->_ub._base == fp->_ubuf) { 34 /* 35 * Get a new buffer (rather than expanding the old one). 36 */ 37 if ((p = malloc((size_t)BUFSIZ)) == NULL) 38 return (EOF); 39 fp->_ub._base = p; 40 fp->_ub._size = BUFSIZ; 41 p += BUFSIZ - sizeof(fp->_ubuf); 42 for (i = sizeof(fp->_ubuf); --i >= 0;) 43 p[i] = fp->_ubuf[i]; 44 fp->_p = p; 45 return (0); 46 } 47 i = fp->_ub._size; 48 p = realloc(fp->_ub._base, i << 1); 49 if (p == NULL) 50 return (EOF); 51 /* no overlap (hence can use memcpy) because we doubled the size */ 52 (void)memcpy((void *)(p + i), (void *)p, (size_t)i); 53 fp->_p = p + i; 54 fp->_ub._base = p; 55 fp->_ub._size = i << 1; 56 return (0); 57 } 58 59 ungetc(c, fp) 60 int c; 61 register FILE *fp; 62 { 63 if (c == EOF) 64 return (EOF); 65 if (!__sdidinit) 66 __sinit(); 67 if ((fp->_flags & __SRD) == 0) { 68 /* 69 * Not already reading: no good unless reading-and-writing. 70 * Otherwise, flush any current write stuff. 71 */ 72 if ((fp->_flags & __SRW) == 0) 73 return (EOF); 74 if (fp->_flags & __SWR) { 75 if (__sflush(fp)) 76 return (EOF); 77 fp->_flags &= ~__SWR; 78 fp->_w = 0; 79 fp->_lbfsize = 0; 80 } 81 fp->_flags |= __SRD; 82 } 83 c = (unsigned char)c; 84 85 /* 86 * If we are in the middle of ungetc'ing, just continue. 87 * This may require expanding the current ungetc buffer. 88 */ 89 if (HASUB(fp)) { 90 if (fp->_r >= fp->_ub._size && __submore(fp)) 91 return (EOF); 92 *--fp->_p = c; 93 fp->_r++; 94 return (c); 95 } 96 fp->_flags &= ~__SEOF; 97 98 /* 99 * If we can handle this by simply backing up, do so, 100 * but never replace the original character. 101 * (This makes sscanf() work when scanning `const' data.) 102 */ 103 if (fp->_bf._base != NULL && fp->_p > fp->_bf._base && 104 fp->_p[-1] == c) { 105 fp->_p--; 106 fp->_r++; 107 return (c); 108 } 109 110 /* 111 * Create an ungetc buffer. 112 * Initially, we will use the `reserve' buffer. 113 */ 114 fp->_ur = fp->_r; 115 fp->_up = fp->_p; 116 fp->_ub._base = fp->_ubuf; 117 fp->_ub._size = sizeof(fp->_ubuf); 118 fp->_ubuf[sizeof(fp->_ubuf) - 1] = c; 119 fp->_p = &fp->_ubuf[sizeof(fp->_ubuf) - 1]; 120 fp->_r = 1; 121 return (c); 122 } 123