1explain_fprintf(3)         Library Functions Manual         explain_fprintf(3)
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NAME

6       explain_fprintf - explain fprintf(3) errors
7

SYNOPSIS

9       #include <libexplain/fprintf.h>
10       const char *explain_fprintf(FILE *fp, const char *format, ...);
11       const char *explain_errno_fprintf(int errnum, FILE *fp, const char
12       *format, ...);
13       void explain_message_fprintf(char *message, int message_size, FILE *fp,
14       const char *format, ....);
15       void explain_message_errno_fprintf(char *message, int message_size, int
16       errnum, FILE *fp, const char *format, ...);
17

DESCRIPTION

19       These functions may be used to obtain explanations for errors  returned
20       by the fprintf(3) system call.
21
22   explain_fprintf
23       const char *explain_fprintf(FILE *fp, const char *format, ...);
24
25       The  explain_fprintf  function  is  used to obtain an explanation of an
26       error returned by the fprintf(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
30       The errno global variable will be used to obtain the error value to  be
31       decoded.
32
33       fp      The  original  fp,  exactly  as passed to the fprintf(3) system
34               call.
35
36       format  The original format, exactly as passed to the fprintf(3) system
37               call.
38
39       Returns:
40               The message explaining the error. This message buffer is shared
41               by all libexplain functions which do not  supply  a  buffer  in
42               their argument list.  This will be overwritten by the next call
43               to any libexplain function which shares this buffer,  including
44               other threads.
45
46       Note: This function is not thread safe, because it shares a return buf‐
47       fer across all threads, and many other functions in this library.
48
49       Example: This function is intended to be used in a fashion  similar  to
50       the following example:
51              errno = EINVAL;
52              int result = fprintf(fp, format, ...);
53              if (result < 0)
54              {
55                  fprintf(stderr, "%s\n", explain_fprintf(fp, format, ...));
56                  exit(EXIT_FAILURE);
57              }
58
59       The   above   code   example   is   available   pre‐packaged   as   the
60       explain_fprintf_or_die(3) function.
61
62   explain_errno_fprintf
63       const char *explain_errno_fprintf(int errnum, FILE *fp, const char
64       *format, ...);
65
66       The  explain_errno_fprintf function is used to obtain an explanation of
67       an error returned by the fprintf(3) system call. The least the  message
68       will  contain  is  the value of strerror(errno), but usually it will do
69       much better, and indicate the underlying cause in more detail.
70
71       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
77       fp      The original fp, exactly as passed  to  the  fprintf(3)  system
78               call.
79
80       format  The original format, exactly as passed to the fprintf(3) system
81               call.
82
83       Returns:
84               The message explaining the error. This message buffer is shared
85               by  all  libexplain  functions  which do not supply a buffer in
86               their argument list.  This will be overwritten by the next call
87               to  any libexplain function which shares this buffer, including
88               other threads.
89
90       Note: This function is not thread safe, because it shares a return buf‐
91       fer across all threads, and many other functions in this library.
92
93       Example:  This  function is intended to be used in a fashion similar to
94       the following example:
95              errno = EINVAL;
96              int result = fprintf(fp, format, ...);
97              if (result < 0)
98              {
99                  int err = errno;
100                  fprintf(stderr, "%s\n", explain_errno_fprintf(err, fp, for‐
101                  mat, ...));
102                  exit(EXIT_FAILURE);
103              }
104
105       The   above   code   example   is   available   pre‐packaged   as   the
106       explain_fprintf_or_die(3) function.
107
108   explain_message_fprintf
109       void explain_message_fprintf(char *message, int message_size, FILE *fp,
110       const char *format, ...);
111
112       The  explain_message_fprintf  function is used to obtain an explanation
113       of an error returned by the fprintf(3) system call. The least the  mes‐
114       sage  will contain is the value of strerror(errno), but usually it will
115       do much better, and indicate the underlying cause in more detail.
116
117       The errno global variable will be used to obtain the error value to  be
118       decoded.
119
120       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
124       message_size
125               The  size  in  bytes  of  the  location  in  which to store the
126               returned message.
127
128       fp      The original fp, exactly as passed  to  the  fprintf(3)  system
129               call.
130
131       format  The original format, exactly as passed to the fprintf(3) system
132               call.
133
134       Example: This function is intended to be used in a fashion  similar  to
135       the following example:
136              errno = EINVAL;
137              int result = fprintf(fp, format, ...);
138              if (result < 0)
139              {
140                  char message[3000];
141                  explain_message_fprintf(message, sizeof(message), fp, for‐
142                  mat, ...);
143                  fprintf(stderr, "%s\n", message);
144                  exit(EXIT_FAILURE);
145              }
146
147       The   above   code   example   is   available   pre‐packaged   as   the
148       explain_fprintf_or_die(3) function.
149
150   explain_message_errno_fprintf
151       void explain_message_errno_fprintf(char *message, int message_size, int
152       errnum, FILE *fp, const char *format, ...);
153
154       The explain_message_errno_fprintf function is used to obtain an  expla‐
155       nation  of  an  error returned by the fprintf(3) system call. The least
156       the message will contain is the value of strerror(errno),  but  usually
157       it  will  do  much  better,  and  indicate the underlying cause in more
158       detail.
159
160       message The location in which to store the returned message. If a suit‐
161               able message return buffer is supplied, this function is thread
162               safe.
163
164       message_size
165               The size in bytes  of  the  location  in  which  to  store  the
166               returned message.
167
168       errnum  The  error value to be decoded, usually obtained from the errno
169               global variable just before this function is  called.  This  is
170               necessary  if you need to call any code between the system call
171               to be explained and this function, because many libc  functions
172               will alter the value of errno.
173
174       fp      The  original  fp,  exactly  as passed to the fprintf(3) system
175               call.
176
177       format  The original format, exactly as passed to the fprintf(3) system
178               call.
179
180       Example:  This  function is intended to be used in a fashion similar to
181       the following example:
182              errno = EINVAL;
183              int result = fprintf(fp, format, ...);
184              if (result < 0)
185              {
186                  int err = errno;
187                  char message[3000];
188                  explain_message_errno_fprintf(message, sizeof(message), err,
189                  fp, format, ...);
190                  fprintf(stderr, "%s\n", message);
191                  exit(EXIT_FAILURE);
192              }
193
194       The   above   code   example   is   available   pre‐packaged   as   the
195       explain_fprintf_or_die(3) function.
196

SEE ALSO

198       fprintf(3)
199               formatted output conversion
200
201       explain_fprintf_or_die(3)
202               formatted output conversion and report errors
203
205       libexplain version 0.40
206       Copyright (C) 2010 Peter Miller
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209
210                                                            explain_fprintf(3)
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