1explain_ftell(3) Library Functions Manual explain_ftell(3)
2
6 explain_ftell - explain ftell(3) errors
7
9 #include <libexplain/ftell.h>
10 const char *explain_ftell(FILE *fp);
11 const char *explain_errno_ftell(int errnum, FILE *fp);
12 void explain_message_ftell(char *message, int message_size, FILE *fp);
13 void explain_message_errno_ftell(char *message, int message_size, int
14 errnum, FILE *fp);
15
17 These functions may be used to obtain explanations for errors returned
18 by the ftell(3) system call.
19 explain_ftell
21 const char *explain_ftell(FILE *fp);
22 The explain_ftell function is used to obtain an explanation of an error
24 returned by the ftell(3) system call. The least the message will con‐
25 tain is the value of strerror(errno), but usually it will do much bet‐
26 ter, and indicate the underlying cause in more detail.
27 The errno global variable will be used to obtain the error value to be
29 decoded.
30 fp The original fp, exactly as passed to the ftell(3) system call.
32 Returns:
34 The message explaining the error. This message buffer is shared
35 by all libexplain functions which do not supply a buffer in
36 their argument list. This will be overwritten by the next call
37 to any libexplain function which shares this buffer, including
38 other threads.
39 Note: This function is not thread safe, because it shares a return buf‐
41 fer across all threads, and many other functions in this library.
42 Example: This function is intended to be used in a fashion similar to
44 the following example:
45 long result = ftell(fp);
46 if (result < 0)
47 {
48 fprintf(stderr, "%s\n", explain_ftell(fp));
49 exit(EXIT_FAILURE);
50 }
51 The above code example is available pre‐packaged as the
53 explain_ftell_or_die(3) function.
54 explain_errno_ftell
56 const char *explain_errno_ftell(int errnum, FILE *fp);
57 The explain_errno_ftell function is used to obtain an explanation of an
59 error returned by the ftell(3) system call. The least the message will
60 contain is the value of strerror(errno), but usually it will do much
61 better, and indicate the underlying cause in more detail.
62 errnum The error value to be decoded, usually obtained from the errno
64 global variable just before this function is called. This is
65 necessary if you need to call any code between the system call
66 to be explained and this function, because many libc functions
67 will alter the value of errno.
68 fp The original fp, exactly as passed to the ftell(3) system call.
70 Returns:
72 The message explaining the error. This message buffer is shared
73 by all libexplain functions which do not supply a buffer in
74 their argument list. This will be overwritten by the next call
75 to any libexplain function which shares this buffer, including
76 other threads.
77 Note: This function is not thread safe, because it shares a return buf‐
79 fer across all threads, and many other functions in this library.
80 Example: This function is intended to be used in a fashion similar to
82 the following example:
83 long result = ftell(fp);
84 if (result < 0)
85 {
86 int err = errno;
87 fprintf(stderr, "%s\n", explain_errno_ftell(err, fp));
88 exit(EXIT_FAILURE);
89 }
90 The above code example is available pre‐packaged as the
92 explain_ftell_or_die(3) function.
93 explain_message_ftell
95 void explain_message_ftell(char *message, int message_size, FILE *fp);
96 The explain_message_ftell function is used to obtain an explanation of
98 an error returned by the ftell(3) system call. The least the message
99 will contain is the value of strerror(errno), but usually it will do
100 much better, and indicate the underlying cause in more detail.
101 The errno global variable will be used to obtain the error value to be
103 decoded.
104 message The location in which to store the returned message. If a suit‐
106 able message return buffer is supplied, this function is thread
107 safe.
108 message_size
110 The size in bytes of the location in which to store the
111 returned message.
112 fp The original fp, exactly as passed to the ftell(3) system call.
114 Example: This function is intended to be used in a fashion similar to
116 the following example:
117 long result = ftell(fp);
118 if (result < 0)
119 {
120 char message[3000];
121 explain_message_ftell(message, sizeof(message), fp);
122 fprintf(stderr, "%s\n", message);
123 exit(EXIT_FAILURE);
124 }
125 The above code example is available pre‐packaged as the
127 explain_ftell_or_die(3) function.
128 explain_message_errno_ftell
130 void explain_message_errno_ftell(char *message, int message_size, int
131 errnum, FILE *fp);
132 The explain_message_errno_ftell function is used to obtain an explana‐
134 tion of an error returned by the ftell(3) system call. The least the
135 message will contain is the value of strerror(errno), but usually it
136 will do much better, and indicate the underlying cause in more detail.
137 message The location in which to store the returned message. If a suit‐
139 able message return buffer is supplied, this function is thread
140 safe.
141 message_size
143 The size in bytes of the location in which to store the
144 returned message.
145 errnum The error value to be decoded, usually obtained from the errno
147 global variable just before this function is called. This is
148 necessary if you need to call any code between the system call
149 to be explained and this function, because many libc functions
150 will alter the value of errno.
151 fp The original fp, exactly as passed to the ftell(3) system call.
153 Example: This function is intended to be used in a fashion similar to
155 the following example:
156 long result = ftell(fp);
157 if (result < 0)
158 {
159 int err = errno;
160 char message[3000];
161 explain_message_errno_ftell(message, sizeof(message), err,
162 fp);
163 fprintf(stderr, "%s\n", message);
164 exit(EXIT_FAILURE);
165 }
166 The above code example is available pre‐packaged as the
168 explain_ftell_or_die(3) function.
169
171 ftell(3)
172 reposition a stream
173 explain_ftell_or_die(3)
175 reposition a stream and report errors
176
178 libexplain version 1.4
179 Copyright (C) 2010 Peter Miller
180 explain_ftell(3)