1explain_dup2(3) Library Functions Manual explain_dup2(3)
2
6 explain_dup2 - explain dup2(2) errors
7
9 #include <libexplain/dup2.h>
10 const char *explain_dup2(int oldfd, int newfd);
11 const char *explain_errno_dup2(int errnum, int oldfd, int newfd);
12 void explain_message_dup2(char *message, int message_size, int oldfd,
13 int newfd);
14 void explain_message_errno_dup2(char *message, int message_size, int
15 errnum, int oldfd, int newfd);
16
18 These functions may be used to obtain explanations for errors returned
19 by the dup2(2) system call.
20 explain_dup2
22 const char *explain_dup2(int oldfd, int newfd);
23 The explain_dup2 function is used to obtain an explanation of an error
25 returned by the dup2(2) system call. The least the message will con‐
26 tain is the value of strerror(errno), but usually it will do much bet‐
27 ter, and indicate the underlying cause in more detail.
28 The errno global variable will be used to obtain the error value to be
30 decoded.
31 This function is intended to be used in a fashion similar to the fol‐
33 lowing example:
34 if (dup2(oldfd, newfd) < 0)
35 {
36 fprintf(stderr, "%s\n", explain_dup2(oldfd, newfd));
37 exit(EXIT_FAILURE);
38 }
39 oldfd The original oldfd, exactly as passed to the dup2(2) system
41 call.
42 newfd The original newfd, exactly as passed to the dup2(2) system
44 call.
45 Returns:
47 The message explaining the error. This message buffer is
48 shared by all libexplain functions which do not supply a buffer
49 in their argument list. This will be overwritten by the next
50 call to any libexplain function which shares this buffer,
51 including other threads.
52 Note: This function is not thread safe, because it shares a return buf‐
54 fer across all threads, and many other functions in this library.
55 explain_errno_dup2
57 const char *explain_errno_dup2(int errnum, int oldfd, int newfd);
58 The explain_errno_dup2 function is used to obtain an explanation of an
60 error returned by the dup2(2) system call. The least the message will
61 contain is the value of strerror(errnum), but usually it will do much
62 better, and indicate the underlying cause in more detail.
63 This function is intended to be used in a fashion similar to the fol‐
65 lowing example:
66 if (dup2(oldfd, newfd) < 0)
67 {
68 int err = errno;
69 fprintf(stderr, "%s\n", explain_errno_dup2(err, oldfd, newfd));
70 exit(EXIT_FAILURE);
71 }
72 errnum The error value to be decoded, usually obtained from the errno
74 global variable just before this function is called. This is
75 necessary if you need to call any code between the system call
76 to be explained and this function, because many libc functions
77 will alter the value of errno.
78 oldfd The original oldfd, exactly as passed to the dup2(2) system
80 call.
81 newfd The original newfd, exactly as passed to the dup2(2) system
83 call.
84 Returns:
86 The message explaining the error. This message buffer is
87 shared by all libexplain functions which do not supply a buffer
88 in their argument list. This will be overwritten by the next
89 call to any libexplain function which shares this buffer,
90 including 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 explain_message_dup2
96 void explain_message_dup2(char *message, int message_size, int oldfd,
97 int newfd);
98 The explain_message_dup2 function may be used to obtain an explanation
100 of an error returned by the dup2(2) system call. The least the message
101 will contain is the value of strerror(errno), but usually it will do
102 much better, and indicate the underlying cause in more detail.
103 The errno global variable will be used to obtain the error value to be
105 decoded.
106 This function is intended to be used in a fashion similar to the fol‐
108 lowing example:
109 if (dup2(oldfd, newfd) < 0)
110 {
111 char message[3000];
112 explain_message_dup2(message, sizeof(message), oldfd, newfd);
113 fprintf(stderr, "%s\n", message);
114 exit(EXIT_FAILURE);
115 }
116 message The location in which to store the returned message. If a
118 suitable message return buffer is supplied, this function is
119 thread safe.
120 message_size
122 The size in bytes of the location in which to store the
123 returned message.
124 oldfd The original oldfd, exactly as passed to the dup2(2) system
126 call.
127 newfd The original newfd, exactly as passed to the dup2(2) system
129 call.
130 explain_message_errno_dup2
132 void explain_message_errno_dup2(char *message, int message_size, int
133 errnum, int oldfd, int newfd);
134 The explain_message_errno_dup2 function may be used to obtain an expla‐
136 nation of an error returned by the dup2(2) system call. The least the
137 message will contain is the value of strerror(errnum), but usually it
138 will do much better, and indicate the underlying cause in more detail.
139 This function is intended to be used in a fashion similar to the fol‐
141 lowing example:
142 if (dup2(oldfd, newfd) < 0)
143 {
144 int err = errno;
145 char message[3000];
146 explain_message_errno_dup2(message, sizeof(message), err, oldfd, newfd);
147 fprintf(stderr, "%s\n", message);
148 exit(EXIT_FAILURE);
149 }
150 message The location in which to store the returned message. If a
152 suitable message return buffer is supplied, this function is
153 thread safe.
154 message_size
156 The size in bytes of the location in which to store the
157 returned message.
158 errnum The error value to be decoded, usually obtained from the errno
160 global variable just before this function is called. This is
161 necessary if you need to call any code between the system call
162 to be explained and this function, because many libc functions
163 will alter the value of errno.
164 oldfd The original oldfd, exactly as passed to the dup2(2) system
166 call.
167 newfd The original newfd, exactly as passed to the dup2(2) system
169 call.
170
172 dup2(2) duplicate a file descriptor
173 explain_dup2_or_die(3)
175 duplicate a file descriptor and report errors
176
178 libexplain version 1.4
179 Copyright (C) 2008 Peter Miller
180 explain_dup2(3)