1explain_unsetenv(3) Library Functions Manual explain_unsetenv(3)
2
6 explain_unsetenv - explain unsetenv(3) errors
7
9 #include <libexplain/unsetenv.h>
10 const char *explain_unsetenv(const char *name);
11 const char *explain_errno_unsetenv(int errnum, const char *name);
12 void explain_message_unsetenv(char *message, int message_size, const
13 char *name);
14 void explain_message_errno_unsetenv(char *message, int message_size,
15 int errnum, const char *name);
16
18 These functions may be used to obtain explanations for errors returned
19 by the unsetenv(3) system call.
20 explain_unsetenv
22 const char *explain_unsetenv(const char *name);
23 The explain_unsetenv function is used to obtain an explanation of an
25 error returned by the unsetenv(3) system call. The least the message
26 will contain is the value of strerror(errno), but usually it will do
27 much better, 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 name The original name, exactly as passed to the unsetenv(3) system
33 call.
34 Returns:
36 The message explaining the error. This message buffer is shared
37 by all libexplain functions which do not supply a buffer in
38 their argument list. This will be overwritten by the next call
39 to any libexplain function which shares this buffer, including
40 other threads.
41 Note: This function is not thread safe, because it shares a return buf‐
43 fer across all threads, and many other functions in this library.
44 Example: This function is intended to be used in a fashion similar to
46 the following example:
47 if (unsetenv(name) < 0)
48 {
49 fprintf(stderr, "%s\n", explain_unsetenv(name));
50 exit(EXIT_FAILURE);
51 }
52 The above code example is available pre‐packaged as the
54 explain_unsetenv_or_die(3) function.
55 explain_errno_unsetenv
57 const char *explain_errno_unsetenv(int errnum, const char *name);
58 The explain_errno_unsetenv function is used to obtain an explanation of
60 an error returned by the unsetenv(3) system call. The least the mes‐
61 sage will contain is the value of strerror(errno), but usually it will
62 do much better, and indicate the underlying cause in more detail.
63 errnum The error value to be decoded, usually obtained from the errno
65 global variable just before this function is called. This is
66 necessary if you need to call any code between the system call
67 to be explained and this function, because many libc functions
68 will alter the value of errno.
69 name The original name, exactly as passed to the unsetenv(3) system
71 call.
72 Returns:
74 The message explaining the error. This message buffer is shared
75 by all libexplain functions which do not supply a buffer in
76 their argument list. This will be overwritten by the next call
77 to any libexplain function which shares this buffer, including
78 other threads.
79 Note: This function is not thread safe, because it shares a return buf‐
81 fer across all threads, and many other functions in this library.
82 Example: This function is intended to be used in a fashion similar to
84 the following example:
85 if (unsetenv(name) < 0)
86 {
87 int err = errno;
88 fprintf(stderr, "%s\n", explain_errno_unsetenv(err, name));
89 exit(EXIT_FAILURE);
90 }
91 The above code example is available pre‐packaged as the
93 explain_unsetenv_or_die(3) function.
94 explain_message_unsetenv
96 void explain_message_unsetenv(char *message, int message_size, const
97 char *name);
98 The explain_message_unsetenv function is used to obtain an explanation
100 of an error returned by the unsetenv(3) system call. The least the
101 message will contain is the value of strerror(errno), but usually it
102 will do 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 message The location in which to store the returned message. If a suit‐
108 able message return buffer is supplied, this function is thread
109 safe.
110 message_size
112 The size in bytes of the location in which to store the
113 returned message.
114 name The original name, exactly as passed to the unsetenv(3) system
116 call.
117 Example: This function is intended to be used in a fashion similar to
119 the following example:
120 if (unsetenv(name) < 0)
121 {
122 char message[3000];
123 explain_message_unsetenv(message, sizeof(message), name);
124 fprintf(stderr, "%s\n", message);
125 exit(EXIT_FAILURE);
126 }
127 The above code example is available pre‐packaged as the
129 explain_unsetenv_or_die(3) function.
130 explain_message_errno_unsetenv
132 void explain_message_errno_unsetenv(char *message, int message_size,
133 int errnum, const char *name);
134 The explain_message_errno_unsetenv function is used to obtain an expla‐
136 nation of an error returned by the unsetenv(3) system call. The least
137 the message will contain is the value of strerror(errno), but usually
138 it will do much better, and indicate the underlying cause in more
139 detail.
140 message The location in which to store the returned message. If a suit‐
142 able message return buffer is supplied, this function is thread
143 safe.
144 message_size
146 The size in bytes of the location in which to store the
147 returned message.
148 errnum The error value to be decoded, usually obtained from the errno
150 global variable just before this function is called. This is
151 necessary if you need to call any code between the system call
152 to be explained and this function, because many libc functions
153 will alter the value of errno.
154 name The original name, exactly as passed to the unsetenv(3) system
156 call.
157 Example: This function is intended to be used in a fashion similar to
159 the following example:
160 if (unsetenv(name) < 0)
161 {
162 int err = errno;
163 char message[3000];
164 explain_message_errno_unsetenv(message, sizeof(message),
165 err, name);
166 fprintf(stderr, "%s\n", message);
167 exit(EXIT_FAILURE);
168 }
169 The above code example is available pre‐packaged as the
171 explain_unsetenv_or_die(3) function.
172
174 unsetenv(3)
175 change or add an environment variable
176 explain_unsetenv_or_die(3)
178 change or add an environment variable and report errors
179
181 libexplain version 1.4
182 Copyright (C) 2010 Peter Miller
183 explain_unsetenv(3)