1explain_vfprintf(3) Library Functions Manual explain_vfprintf(3)
2
6 explain_vfprintf - explain vfprintf(3) errors
7
9 #include <libexplain/vfprintf.h>
10 const char *explain_vfprintf(FILE *fp, const char *format, va_list ap);
11 const char *explain_errno_vfprintf(int errnum, FILE *fp, const char
12 *format, va_list ap);
13 void explain_message_vfprintf(char *message, int message_size, FILE
14 *fp, const char *format, va_list ap);
15 void explain_message_errno_vfprintf(char *message, int message_size,
16 int errnum, FILE *fp, const char *format, va_list ap);
17
19 These functions may be used to obtain explanations for errors returned
20 by the vfprintf(3) system call.
21 explain_vfprintf
23 const char *explain_vfprintf(FILE *fp, const char *format, va_list ap);
24 The explain_vfprintf function is used to obtain an explanation of an
26 error returned by the vfprintf(3) system call. The least the message
27 will contain is the value of strerror(errno), but usually it will do
28 much better, 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 vfprintf(3) system
34 call.
35 format The original format, exactly as passed to the vfprintf(3) sys‐
37 tem call.
38 ap The original ap, exactly as passed to the vfprintf(3) system
40 call.
41 Returns:
43 The message explaining the error. This message buffer is shared
44 by all libexplain functions which do not supply a buffer in
45 their argument list. This will be overwritten by the next call
46 to any libexplain function which shares this buffer, including
47 other threads.
48 Note: This function is not thread safe, because it shares a return buf‐
50 fer across all threads, and many other functions in this library.
51 Example: This function is intended to be used in a fashion similar to
53 the following example:
54 errno = EINVAL; if (vfprintf(fp, format, ap) < 0)
55 {
56 fprintf(stderr, "%s\n", explain_vfprintf(fp, format, ap));
57 exit(EXIT_FAILURE);
58 }
59 The above code example is available pre‐packaged as the
61 explain_vfprintf_or_die(3) function.
62 explain_errno_vfprintf
64 const char *explain_errno_vfprintf(int errnum, FILE *fp, const char
65 *format, va_list ap);
66 The explain_errno_vfprintf function is used to obtain an explanation of
68 an error returned by the vfprintf(3) system call. The least the mes‐
69 sage will contain is the value of strerror(errno), but usually it will
70 do much better, and indicate the underlying cause in more detail.
71 errnum The error value to be decoded, usually obtained from the errno
73 global variable just before this function is called. This is
74 necessary if you need to call any code between the system call
75 to be explained and this function, because many libc functions
76 will alter the value of errno.
77 fp The original fp, exactly as passed to the vfprintf(3) system
79 call.
80 format The original format, exactly as passed to the vfprintf(3) sys‐
82 tem call.
83 ap The original ap, exactly as passed to the vfprintf(3) system
85 call.
86 Returns:
88 The message explaining the error. This message buffer is shared
89 by all libexplain functions which do not supply a buffer in
90 their argument list. This will be overwritten by the next call
91 to any libexplain function which shares this buffer, including
92 other threads.
93 Note: This function is not thread safe, because it shares a return buf‐
95 fer across all threads, and many other functions in this library.
96 Example: This function is intended to be used in a fashion similar to
98 the following example:
99 errno = EINVAL; if (vfprintf(fp, format, ap) < 0)
100 {
101 int err = errno;
102 fprintf(stderr, "%s\n", explain_errno_vfprintf(err, fp, for‐
103 mat, ap));
104 exit(EXIT_FAILURE);
105 }
106 The above code example is available pre‐packaged as the
108 explain_vfprintf_or_die(3) function.
109 explain_message_vfprintf
111 void explain_message_vfprintf(char *message, int message_size, FILE
112 *fp, const char *format, va_list ap);
113 The explain_message_vfprintf function is used to obtain an explanation
115 of an error returned by the vfprintf(3) system call. The least the
116 message will contain is the value of strerror(errno), but usually it
117 will do much better, and indicate the underlying cause in more detail.
118 The errno global variable will be used to obtain the error value to be
120 decoded.
121 message The location in which to store the returned message. If a suit‐
123 able message return buffer is supplied, this function is thread
124 safe.
125 message_size
127 The size in bytes of the location in which to store the
128 returned message.
129 fp The original fp, exactly as passed to the vfprintf(3) system
131 call.
132 format The original format, exactly as passed to the vfprintf(3) sys‐
134 tem call.
135 ap The original ap, exactly as passed to the vfprintf(3) system
137 call.
138 Example: This function is intended to be used in a fashion similar to
140 the following example:
141 errno = EINVAL; if (vfprintf(fp, format, ap) < 0)
142 {
143 char message[3000];
144 explain_message_vfprintf(message, sizeof(message), fp, for‐
145 mat, ap);
146 fprintf(stderr, "%s\n", message);
147 exit(EXIT_FAILURE);
148 }
149 The above code example is available pre‐packaged as the
151 explain_vfprintf_or_die(3) function.
152 explain_message_errno_vfprintf
154 void explain_message_errno_vfprintf(char *message, int message_size,
155 int errnum, FILE *fp, const char *format, va_list ap);
156 The explain_message_errno_vfprintf function is used to obtain an expla‐
158 nation of an error returned by the vfprintf(3) system call. The least
159 the message will contain is the value of strerror(errno), but usually
160 it will do much better, and indicate the underlying cause in more
161 detail.
162 message The location in which to store the returned message. If a suit‐
164 able message return buffer is supplied, this function is thread
165 safe.
166 message_size
168 The size in bytes of the location in which to store the
169 returned message.
170 errnum The error value to be decoded, usually obtained from the errno
172 global variable just before this function is called. This is
173 necessary if you need to call any code between the system call
174 to be explained and this function, because many libc functions
175 will alter the value of errno.
176 fp The original fp, exactly as passed to the vfprintf(3) system
178 call.
179 format The original format, exactly as passed to the vfprintf(3) sys‐
181 tem call.
182 ap The original ap, exactly as passed to the vfprintf(3) system
184 call.
185 Example: This function is intended to be used in a fashion similar to
187 the following example:
188 errno = EINVAL; if (vfprintf(fp, format, ap) < 0)
189 {
190 int err = errno;
191 char message[3000];
192 explain_message_errno_vfprintf(message, sizeof(message),
193 err, fp, format, ap);
194 fprintf(stderr, "%s\n", message);
195 exit(EXIT_FAILURE);
196 }
197 The above code example is available pre‐packaged as the
199 explain_vfprintf_or_die(3) function.
200
202 vfprintf(3)
203 formatted output conversion
204 explain_vfprintf_or_die(3)
206 formatted output conversion and report errors
207
209 libexplain version 1.4
210 Copyright (C) 2010 Peter Miller
211 explain_vfprintf(3)