1 /*
2 * Copyright (c) 1990 The Regents of the University of California.
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms are permitted
6 * provided that the above copyright notice and this paragraph are
7 * duplicated in all such forms and that any documentation,
8 * and/or other materials related to such
9 * distribution and use acknowledge that the software was developed
10 * by the University of California, Berkeley. The name of the
11 * University may not be used to endorse or promote products derived
12 * from this software without specific prior written permission.
13 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
14 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
15 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
16 */
17 /*
18 FUNCTION
19 <<ungetc>>---push data back into a stream
20
21 INDEX
22 ungetc
23 INDEX
24 _ungetc_r
25
26 SYNOPSIS
27 #include <stdio.h>
28 int ungetc(int <[c]>, FILE *<[stream]>);
29
30 int ungetc( int <[c]>, FILE *<[stream]>);
31
32 DESCRIPTION
33 <<ungetc>> is used to return bytes back to <[stream]> to be read again.
34 If <[c]> is EOF, the stream is unchanged. Otherwise, the unsigned
35 char <[c]> is put back on the stream, and subsequent reads will see
36 the bytes pushed back in reverse order. Pushed byes are lost if the
37 stream is repositioned, such as by <<fseek>>, <<fsetpos>>, or
38 <<rewind>>.
39
40 The underlying file is not changed, but it is possible to push back
41 something different than what was originally read. Ungetting a
42 character will clear the end-of-stream marker, and decrement the file
43 position indicator. Pushing back beyond the beginning of a file gives
44 unspecified behavior.
45
46 The alternate function <<_ungetc_r>> is a reentrant version. The
47 extra argument <[reent]> is a pointer to a reentrancy structure.
48
49 RETURNS
50 The character pushed back, or <<EOF>> on error.
51
52 PORTABILITY
53 ANSI C requires <<ungetc>>, but only requires a pushback buffer of one
54 byte; although this implementation can handle multiple bytes, not all
55 can. Pushing back a signed char is a common application bug.
56
57 Supporting OS subroutines required: <<sbrk>>.
58 */
59
60 #if defined(LIBC_SCCS) && !defined(lint)
61 static char sccsid[] = "%W% (Berkeley) %G%";
62 #endif /* LIBC_SCCS and not lint */
63
64 #define _DEFAULT_SOURCE
65 #include <_ansi.h>
66 #include <stdio.h>
67 #include <stdlib.h>
68 #include <string.h>
69 #include "local.h"
70
71 /*
72 * Expand the ungetc buffer `in place'. That is, adjust fp->_p when
73 * the buffer moves, so that it points the same distance from the end,
74 * and move the bytes in the buffer around as necessary so that they
75 * are all at the end (stack-style).
76 */
77
78 /*static*/
79 int
__submore(register FILE * fp)80 __submore (
81 register FILE *fp)
82 {
83 register int i;
84 register unsigned char *p;
85
86 if (fp->_ub._base == fp->_ubuf)
87 {
88 /*
89 * Get a new buffer (rather than expanding the old one).
90 */
91 if ((p = (unsigned char *) malloc ((size_t) BUFSIZ)) == NULL)
92 return EOF;
93 fp->_ub._base = p;
94 fp->_ub._size = BUFSIZ;
95 p += BUFSIZ - sizeof (fp->_ubuf);
96 for (i = sizeof (fp->_ubuf); --i >= 0;)
97 p[i] = fp->_ubuf[i];
98 fp->_p = p;
99 return 0;
100 }
101 i = fp->_ub._size;
102 p = (unsigned char *) realloc ((void *) (fp->_ub._base), i << 1);
103 if (p == NULL)
104 return EOF;
105 (void) memcpy ((void *) (p + i), (void *) p, (size_t) i);
106 fp->_p = p + i;
107 fp->_ub._base = p;
108 fp->_ub._size = i << 1;
109 return 0;
110 }
111
112 int
ungetc(int c,register FILE * fp)113 ungetc (
114 int c,
115 register FILE *fp)
116 {
117 if (c == EOF)
118 return (EOF);
119
120 /* Ensure stdio has been initialized.
121 ??? Might be able to remove this as some other stdio routine should
122 have already been called to get the char we are un-getting. */
123
124 CHECK_INIT (rptr, fp);
125
126 _newlib_flockfile_start (fp);
127
128 ORIENT (fp, -1);
129
130 /* After ungetc, we won't be at eof anymore */
131 fp->_flags &= ~__SEOF;
132
133 if ((fp->_flags & __SRD) == 0)
134 {
135 /*
136 * Not already reading: no good unless reading-and-writing.
137 * Otherwise, flush any current write stuff.
138 */
139 if ((fp->_flags & __SRW) == 0)
140 {
141 _newlib_flockfile_exit (fp);
142 return EOF;
143 }
144 if (fp->_flags & __SWR)
145 {
146 if (fflush ( fp))
147 {
148 _newlib_flockfile_exit (fp);
149 return EOF;
150 }
151 fp->_flags &= ~__SWR;
152 fp->_w = 0;
153 fp->_lbfsize = 0;
154 }
155 fp->_flags |= __SRD;
156 }
157 c = (unsigned char) c;
158
159 /*
160 * If we are in the middle of ungetc'ing, just continue.
161 * This may require expanding the current ungetc buffer.
162 */
163
164 if (HASUB (fp))
165 {
166 if (fp->_r >= fp->_ub._size && __submore (fp))
167 {
168 _newlib_flockfile_exit (fp);
169 return EOF;
170 }
171 *--fp->_p = c;
172 fp->_r++;
173 _newlib_flockfile_exit (fp);
174 return c;
175 }
176
177 /*
178 * If we can handle this by simply backing up, do so,
179 * but never replace the original character.
180 * (This makes sscanf() work when scanning `const' data.)
181 */
182
183 if (fp->_bf._base != NULL && fp->_p > fp->_bf._base && fp->_p[-1] == c)
184 {
185 fp->_p--;
186 fp->_r++;
187 _newlib_flockfile_exit (fp);
188 return c;
189 }
190
191 /*
192 * Create an ungetc buffer.
193 * Initially, we will use the `reserve' buffer.
194 */
195
196 fp->_ur = fp->_r;
197 fp->_up = fp->_p;
198 fp->_ub._base = fp->_ubuf;
199 fp->_ub._size = sizeof (fp->_ubuf);
200 fp->_ubuf[sizeof (fp->_ubuf) - 1] = c;
201 fp->_p = &fp->_ubuf[sizeof (fp->_ubuf) - 1];
202 fp->_r = 1;
203 _newlib_flockfile_end (fp);
204 return c;
205 }
206
