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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 (&outer_fd, &inner_fd, 0, 0, 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 (fp); | |
101 | TEST_COMPARE (fgetc (fp), 'd'); | |
102 | TEST_COMPARE (fgetc (fp), '\n'); | |
103 | ||
104 | fclose (fp); | |
105 | close (outer_fd); | |
106 | return 0; | |
107 | } | |
108 | ||
109 | #include <support/test-driver.c> |