1 | /* Bug 1190: EOF conditions are supposed to be sticky. |
2 | Copyright (C) 2018 Free Software Foundation. |
3 | Copying and distribution of this file, with or without modification, |
4 | are permitted in any medium without royalty provided the copyright |
5 | notice and this notice are preserved. This file is offered as-is, |
6 | without any warranty. */ |
7 | |
8 | /* ISO C1999 specification of fgetc: |
9 | |
10 | #include <stdio.h> |
11 | int fgetc (FILE *stream); |
12 | |
13 | Description |
14 | |
15 | If the end-of-file indicator for the input stream pointed to by |
16 | stream is not set and a next character is present, the fgetc |
17 | function obtains that character as an unsigned char converted to |
18 | an int and advances the associated file position indicator for |
19 | the stream (if defined). |
20 | |
21 | Returns |
22 | |
23 | If the end-of-file indicator for the stream is set, or if the |
24 | stream is at end-of-file, the end-of-file indicator for the |
25 | stream is set and the fgetc function returns EOF. Otherwise, the |
26 | fgetc function returns the next character from the input stream |
27 | pointed to by stream. If a read error occurs, the error indicator |
28 | for the stream is set and the fgetc function returns EOF. |
29 | |
30 | The requirement to return EOF "if the end-of-file indicator for the |
31 | stream is set" was new in C99; the language in the 1989 edition of |
32 | the standard was ambiguous. Historically, BSD-derived Unix always |
33 | had the C99 behavior, whereas in System V fgetc would attempt to |
34 | call read() again before returning EOF again. Prior to version 2.28, |
35 | glibc followed the System V behavior even though this does not |
36 | comply with C99. |
37 | |
38 | See |
39 | <https://sourceware.org/bugzilla/show_bug.cgi?id=1190>, |
40 | <https://sourceware.org/bugzilla/show_bug.cgi?id=19476>, |
41 | and the thread at |
42 | <https://sourceware.org/ml/libc-alpha/2012-09/msg00343.html> |
43 | for more detail. */ |
44 | |
45 | #include <support/tty.h> |
46 | #include <support/check.h> |
47 | |
48 | #include <fcntl.h> |
49 | #include <stdio.h> |
50 | #include <stdlib.h> |
51 | #include <string.h> |
52 | #include <unistd.h> |
53 | |
54 | #define XWRITE(fd, s, msg) do { \ |
55 | if (write (fd, s, sizeof s - 1) != sizeof s - 1) \ |
56 | { \ |
57 | perror ("write " msg); \ |
58 | return 1; \ |
59 | } \ |
60 | } while (0) |
61 | |
62 | int |
63 | do_test (void) |
64 | { |
65 | /* The easiest way to set up the conditions under which you can |
66 | notice whether the end-of-file indicator is sticky, is with a |
67 | pseudo-tty. This is also the case which applications are most |
68 | likely to care about. And it avoids any question of whether and |
69 | how it is legitimate to access the same physical file with two |
70 | independent FILE objects. */ |
71 | int outer_fd, inner_fd; |
72 | FILE *fp; |
73 | |
74 | support_openpty (a_outer: &outer_fd, a_inner: &inner_fd, a_name: 0, termp: 0, winp: 0); |
75 | fp = fdopen (inner_fd, "r+" ); |
76 | if (!fp) |
77 | { |
78 | perror ("fdopen" ); |
79 | return 1; |
80 | } |
81 | |
82 | XWRITE (outer_fd, "abc\n\004" , "first line + EOF" ); |
83 | TEST_COMPARE (fgetc (fp), 'a'); |
84 | TEST_COMPARE (fgetc (fp), 'b'); |
85 | TEST_COMPARE (fgetc (fp), 'c'); |
86 | TEST_COMPARE (fgetc (fp), '\n'); |
87 | TEST_COMPARE (fgetc (fp), EOF); |
88 | |
89 | TEST_VERIFY_EXIT (feof (fp)); |
90 | TEST_VERIFY_EXIT (!ferror (fp)); |
91 | |
92 | XWRITE (outer_fd, "d\n" , "second line" ); |
93 | |
94 | /* At this point, there is a new full line of input waiting in the |
95 | kernelside input buffer, but we should still observe EOF from |
96 | stdio, because the end-of-file indicator has not been cleared. */ |
97 | TEST_COMPARE (fgetc (fp), EOF); |
98 | |
99 | /* Clearing EOF should reveal the next line of input. */ |
100 | clearerr (stream: fp); |
101 | TEST_COMPARE (fgetc (fp), 'd'); |
102 | TEST_COMPARE (fgetc (fp), '\n'); |
103 | |
104 | fclose (fp); |
105 | close (fd: outer_fd); |
106 | return 0; |
107 | } |
108 | |
109 | #include <support/test-driver.c> |
110 | |