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comparison lib/fwriteerror.c @ 4709:86c722c44f87

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New module 'fwriteerror'.
author Bruno Haible <bruno@clisp.org>
date Mon, 15 Sep 2003 19:15:22 +0000
parents
children c8676e66b5da
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4708:d4b48bc2b174 4709:86c722c44f87
1 /* Detect write error on a stream.
2 Copyright (C) 2003 Free Software Foundation, Inc.
3 Written by Bruno Haible <bruno@clisp.org>, 2003.
4
5 This program is free software; you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 2, or (at your option)
8 any later version.
9
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
14
15 You should have received a copy of the GNU General Public License
16 along with this program; if not, write to the Free Software Foundation,
17 Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */
18
19 #if HAVE_CONFIG_H
20 # include <config.h>
21 #endif
22
23 /* Specification. */
24 #include "fwriteerror.h"
25
26 #include <errno.h>
27
28 int
29 fwriteerror (FILE *fp)
30 {
31 /* Need to
32 1. test the error indicator of the stream,
33 2. flush the buffers (what fclose() would do), testing for error again.
34 We can equally well swap these steps; this leads to smaller code. */
35
36 /* Clear errno, so that on non-POSIX systems the caller doesn't see a
37 wrong value of errno when we return -1. */
38 errno = 0;
39
40 if (fflush (fp))
41 return -1; /* errno is set here */
42
43 if (ferror (fp))
44 {
45 /* The stream had an error earlier, but its errno was lost. If the
46 error was not temporary, we can get the same errno by writing and
47 flushing one more byte. We can do so because at this point the
48 stream's contents is garbage anyway. */
49 if (fputc ('\0', fp) == EOF)
50 return -1; /* errno is set here */
51 if (fflush (fp))
52 return -1; /* errno is set here */
53 /* Give up on errno. */
54 errno = 0;
55 return -1;
56 }
57
58 return 0;
59 }
60
61
62 #if TEST
63
64 /* Name of a file on which writing fails. On systems without /dev/full,
65 you can choose a filename on a full filesystem. */
66 #define UNWRITABLE_FILE "/dev/full"
67
68 int
69 main ()
70 {
71 static int sizes[] =
72 {
73 511, 512, 513,
74 1023, 1024, 1025,
75 2047, 2048, 2049,
76 4095, 4096, 4097,
77 8191, 8192, 8193
78 };
79 static char dummy[8193];
80 unsigned int i, j;
81
82 for (i = 0; i < sizeof (sizes) / sizeof (sizes[0]); i++)
83 {
84 size_t size = sizes[i];
85
86 for (j = 0; j < 2; j++)
87 {
88 /* Run a test depending on i and j:
89 Write size bytes and then calls fflush if j==1. */
90 FILE *stream = fopen (UNWRITABLE_FILE, "w");
91
92 if (stream == NULL)
93 {
94 fprintf (stderr, "Test %u:%u: could not open file\n", i, j);
95 continue;
96 }
97
98 fwrite (dummy, 347, 1, stream);
99 fwrite (dummy, size - 347, 1, stream);
100 if (j)
101 fflush (stream);
102
103 if (fwriteerror (stream) == -1)
104 {
105 if (errno != ENOSPC)
106 fprintf (stderr, "Test %u:%u: fwriteerror ok, errno = %d\n",
107 i, j, errno);
108 }
109 else
110 fprintf (stderr, "Test %u:%u: fwriteerror found no error!\n",
111 i, j);
112
113 if (fclose (stream))
114 fprintf (stderr, "Test %u:%u: fclose failed, errno = %d\n",
115 i, j, errno);
116 }
117 }
118
119 return 0;
120 }
121
122 #endif