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

6       explain_popen - explain popen(3) errors
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SYNOPSIS

9       #include <libexplain/popen.h>
10       const char *explain_popen(const char *command, const char *flags);
11       const  char *explain_errno_popen(int errnum, const char *command, const
12       char *flags);
13       void explain_message_popen(char *message, int message_size, const  char
14       *command, const char *flags);
15       void  explain_message_errno_popen(char  *message, int message_size, int
16       errnum, const char *command, const char *flags);
17

DESCRIPTION

19       These functions may be used to obtain explanations for errors  returned
20       by the popen(3) system call.
21
22   explain_popen
23       const char *explain_popen(const char *command, const char *flags);
24
25       The explain_popen function is used to obtain an explanation of an error
26       returned by the popen(3) system call.  The least the message will  con‐
27       tain  is the value of strerror(errno), but usually it will do much bet‐
28       ter, 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       This  function  is intended to be used in a fashion similar to the fol‐
34       lowing example:
35              FILE *fp = popen(command, flags);
36              if (!fp)
37              {
38                  fprintf(stderr, "%s\n", explain_popen(command, flags));
39                  exit(EXIT_FAILURE);
40              }
41
42       The   above   code   example   is   available   pre‐packaged   as   the
43       explain_popen_or_die(3) function.
44
45       command The  original command, exactly as passed to the popen(3) system
46               call.
47
48       flags   The original flags, exactly as passed to  the  popen(3)  system
49               call.
50
51       Returns:
52               The  message  explaining  the  error.   This  message buffer is
53               shared by all libexplain functions which do not supply a buffer
54               in  their  argument list.  This will be overwritten by the next
55               call to any  libexplain  function  which  shares  this  buffer,
56               including other threads.
57
58       Note: This function is not thread safe, because it shares a return buf‐
59       fer across all threads, and many other functions in this library.
60
61   explain_errno_popen
62       const char *explain_errno_popen(int errnum, const char *command,  const
63       char *flags);
64
65       The explain_errno_popen function is used to obtain an explanation of an
66       error returned by the popen(3) system call.  The least the message will
67       contain  is  the value of strerror(errnum), but usually it will do much
68       better, and indicate the underlying cause in more detail.
69
70       This function is intended to be used in a fashion similar to  the  fol‐
71       lowing example:
72              FILE *fp = popen(command, flags);
73              if (!fp)
74              {
75                  int err = errno;
76                  fprintf(stderr, "%s\n", explain_errno_popen(err, command, flags));
77                  exit(EXIT_FAILURE);
78              }
79
80       The   above   code   example   is   available   pre‐packaged   as   the
81       explain_popen_or_die(3) function.
82
83       errnum  The error value to be decoded, usually obtained from the  errno
84               global  variable  just before this function is called.  This is
85               necessary if you need to call any code between the system  call
86               to  be explained and this function, because many libc functions
87               will alter the value of errno.
88
89       command The original command, exactly as passed to the popen(3)  system
90               call.
91
92       flags   The  original  flags,  exactly as passed to the popen(3) system
93               call.
94
95       Returns:
96               The message explaining  the  error.   This  message  buffer  is
97               shared by all libexplain functions which do not supply a buffer
98               in their argument list.  This will be overwritten by  the  next
99               call  to  any  libexplain  function  which  shares this buffer,
100               including other threads.
101
102       Note: This function is not thread safe, because it shares a return buf‐
103       fer across all threads, and many other functions in this library.
104
105   explain_message_popen
106       void  explain_message_popen(char *message, int message_size, const char
107       *command, const char *flags);
108
109       The explain_message_popen function may be used to  obtain  an  explana‐
110       tion  of  an error returned by the popen(3) system call.  The least the
111       message will contain is the value of strerror(errno),  but  usually  it
112       will do much better, and indicate the underlying cause in more detail.
113
114       The  errno global variable will be used to obtain the error value to be
115       decoded.
116
117       This function is intended to be used in a fashion similar to  the  fol‐
118       lowing example:
119              FILE *fp = popen(command, flags);
120              if (!fp)
121              {
122                  char message[3000];
123                  explain_message_popen(message, sizeof(message), command, flags);
124                  fprintf(stderr, "%s\n", message);
125                  exit(EXIT_FAILURE);
126              }
127
128       The   above   code   example   is   available   pre‐packaged   as   the
129       explain_popen_or_die(3) function.
130
131       message The location in which to store  the  returned  message.   If  a
132               suitable  message  return  buffer is supplied, this function is
133               thread safe.
134
135       message_size
136               The size in bytes  of  the  location  in  which  to  store  the
137               returned message.
138
139       command The  original command, exactly as passed to the popen(3) system
140               call.
141
142       flags   The original flags, exactly as passed to  the  popen(3)  system
143               call.
144
145   explain_message_errno_popen
146       void  explain_message_errno_popen(char  *message, int message_size, int
147       errnum, const char *command, const char *flags);
148
149       The explain_message_errno_popen function  may  be  used  to  obtain  an
150       explanation  of  an  error  returned  by the popen(3) system call.  The
151       least the message will contain is the value  of  strerror(errnum),  but
152       usually  it  will  do much better, and indicate the underlying cause in
153       more detail.
154
155       This function is intended to be used in a fashion similar to  the  fol‐
156       lowing example:
157              FILE *fp = popen(command, flags);
158              if (!fp)
159              {
160                  int err = errno;
161                  char message[3000];
162                  explain_message_errno_popen(message, sizeof(message),
163                      err, command, flags);
164                  fprintf(stderr, "%s\n", message);
165                  exit(EXIT_FAILURE);
166              }
167
168       The   above   code   example   is   available   pre‐packaged   as   the
169       explain_popen_or_die(3) function.
170
171       message The location in which to store  the  returned  message.   If  a
172               suitable  message  return  buffer is supplied, this function is
173               thread safe.
174
175       message_size
176               The size in bytes  of  the  location  in  which  to  store  the
177               returned message.
178
179       errnum  The  error value to be decoded, usually obtained from the errno
180               global variable just before this function is called.   This  is
181               necessary  if you need to call any code between the system call
182               to be explained and this function, because many libc  functions
183               will alter the value of errno.
184
185       command The  original command, exactly as passed to the popen(3) system
186               call.
187
188       flags   The original flags, exactly as passed to  the  popen(3)  system
189               call.
190

SEE ALSO

192       popen(3)
193               process I/O
194
195       explain_popen_or_die(3)
196               process I/O and report errors
197
199       libexplain version 0.40
200       Copyright (C) 2009 Peter Miller
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204                                                              explain_popen(3)
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