1explain_fseek(3) Library Functions Manual explain_fseek(3)
2
6 explain_fseek - explain fseek(3) errors
7
9 #include <libexplain/fseek.h>
10 const char *explain_fseek(FILE *fp, long offset, int whence);
11 const char *explain_errno_fseek(int errnum, FILE *fp, long offset, int
12 whence);
13 void explain_message_fseek(char *message, int message_size, FILE *fp,
14 long offset, int whence);
15 void explain_message_errno_fseek(char *message, int message_size, int
16 errnum, FILE *fp, long offset, int whence);
17
19 These functions may be used to obtain explanations for errors returned
20 by the fseek(3) system call.
21 explain_fseek
23 const char *explain_fseek(FILE *fp, long offset, int whence);
24 The explain_fseek function is used to obtain an explanation of an error
26 returned by the fseek(3) system call. The least the message will con‐
27 tain is the value of strerror(errno), but usually it will do much bet‐
28 ter, and indicate the underlying cause in more detail.
29 The errno global variable will be used to obtain the error value to be
31 decoded.
32 fp The original fp, exactly as passed to the fseek(3) system call.
34 offset The original offset, exactly as passed to the fseek(3) system
36 call.
37 whence The original whence, exactly as passed to the fseek(3) system
39 call.
40 Returns:
42 The message explaining the error. This message buffer is shared
43 by all libexplain functions which do not supply a buffer in
44 their argument list. This will be overwritten by the next call
45 to any libexplain function which shares this buffer, including
46 other threads.
47 Note: This function is not thread safe, because it shares a return buf‐
49 fer across all threads, and many other functions in this library.
50 Example: This function is intended to be used in a fashion similar to
52 the following example:
53 if (fseek(fp, offset, whence) < 0)
54 {
55 fprintf(stderr, "%s\n", explain_fseek(fp, offset, whence));
56 exit(EXIT_FAILURE);
57 }
58 The above code example is available pre‐packaged as the
60 explain_fseek_or_die(3) function.
61 explain_errno_fseek
63 const char *explain_errno_fseek(int errnum, FILE *fp, long offset, int
64 whence);
65 The explain_errno_fseek function is used to obtain an explanation of an
67 error returned by the fseek(3) system call. The least the message will
68 contain is the value of strerror(errno), but usually it will do much
69 better, and indicate the underlying cause in more detail.
70 errnum The error value to be decoded, usually obtained from the errno
72 global variable just before this function is called. This is
73 necessary if you need to call any code between the system call
74 to be explained and this function, because many libc functions
75 will alter the value of errno.
76 fp The original fp, exactly as passed to the fseek(3) system call.
78 offset The original offset, exactly as passed to the fseek(3) system
80 call.
81 whence The original whence, exactly as passed to the fseek(3) system
83 call.
84 Returns:
86 The message explaining the error. This message buffer is shared
87 by all libexplain functions which do not supply a buffer in
88 their argument list. This will be overwritten by the next call
89 to any libexplain function which shares this buffer, including
90 other threads.
91 Note: This function is not thread safe, because it shares a return buf‐
93 fer across all threads, and many other functions in this library.
94 Example: This function is intended to be used in a fashion similar to
96 the following example:
97 if (fseek(fp, offset, whence) < 0)
98 {
99 int err = errno;
100 fprintf(stderr, "%s\n", explain_errno_fseek(err, fp, offset,
101 whence));
102 exit(EXIT_FAILURE);
103 }
104 The above code example is available pre‐packaged as the
106 explain_fseek_or_die(3) function.
107 explain_message_fseek
109 void explain_message_fseek(char *message, int message_size, FILE *fp,
110 long offset, int whence);
111 The explain_message_fseek function is used to obtain an explanation of
113 an error returned by the fseek(3) system call. The least the message
114 will contain is the value of strerror(errno), but usually it will do
115 much better, and indicate the underlying cause in more detail.
116 The errno global variable will be used to obtain the error value to be
118 decoded.
119 message The location in which to store the returned message. If a suit‐
121 able message return buffer is supplied, this function is thread
122 safe.
123 message_size
125 The size in bytes of the location in which to store the
126 returned message.
127 fp The original fp, exactly as passed to the fseek(3) system call.
129 offset The original offset, exactly as passed to the fseek(3) system
131 call.
132 whence The original whence, exactly as passed to the fseek(3) system
134 call.
135 Example: This function is intended to be used in a fashion similar to
137 the following example:
138 if (fseek(fp, offset, whence) < 0)
139 {
140 char message[3000];
141 explain_message_fseek(message, sizeof(message), fp, offset,
142 whence);
143 fprintf(stderr, "%s\n", message);
144 exit(EXIT_FAILURE);
145 }
146 The above code example is available pre‐packaged as the
148 explain_fseek_or_die(3) function.
149 explain_message_errno_fseek
151 void explain_message_errno_fseek(char *message, int message_size, int
152 errnum, FILE *fp, long offset, int whence);
153 The explain_message_errno_fseek function is used to obtain an explana‐
155 tion of an error returned by the fseek(3) system call. The least the
156 message will contain is the value of strerror(errno), but usually it
157 will do much better, and indicate the underlying cause in more detail.
158 message The location in which to store the returned message. If a suit‐
160 able message return buffer is supplied, this function is thread
161 safe.
162 message_size
164 The size in bytes of the location in which to store the
165 returned message.
166 errnum The error value to be decoded, usually obtained from the errno
168 global variable just before this function is called. This is
169 necessary if you need to call any code between the system call
170 to be explained and this function, because many libc functions
171 will alter the value of errno.
172 fp The original fp, exactly as passed to the fseek(3) system call.
174 offset The original offset, exactly as passed to the fseek(3) system
176 call.
177 whence The original whence, exactly as passed to the fseek(3) system
179 call.
180 Example: This function is intended to be used in a fashion similar to
182 the following example:
183 if (fseek(fp, offset, whence) < 0)
184 {
185 int err = errno;
186 char message[3000];
187 explain_message_errno_fseek(message, sizeof(message), err,
188 fp, offset, whence);
189 fprintf(stderr, "%s\n", message);
190 exit(EXIT_FAILURE);
191 }
192 The above code example is available pre‐packaged as the
194 explain_fseek_or_die(3) function.
195
197 fseek(3)
198 reposition a stream
199 explain_fseek_or_die(3)
201 reposition a stream and report errors
202
204 libexplain version 1.4
205 Copyright (C) 2010 Peter Miller
206 explain_fseek(3)