1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
|
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Error support</title>
<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
<link rel="start" href="index.html" title="Berkeley DB Programmer's Reference Guide" />
<link rel="up" href="am_misc.html" title="Chapter 4. Access Method Wrapup" />
<link rel="prev" href="am_misc_perm.html" title="Retrieved key/data permanence for C/C++" />
<link rel="next" href="am_misc_stability.html" title="Cursor stability" />
</head>
<body>
<div xmlns="" class="navheader">
<div class="libver">
<p>Library Version 12.1.6.1</p>
</div>
<table width="100%" summary="Navigation header">
<tr>
<th colspan="3" align="center">Error support</th>
</tr>
<tr>
<td width="20%" align="left"><a accesskey="p" href="am_misc_perm.html">Prev</a> </td>
<th width="60%" align="center">Chapter 4. Access Method Wrapup </th>
<td width="20%" align="right"> <a accesskey="n" href="am_misc_stability.html">Next</a></td>
</tr>
</table>
<hr />
</div>
<div class="sect1" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h2 class="title" style="clear: both"><a id="am_misc_error"></a>Error support</h2>
</div>
</div>
</div>
<p>
Berkeley DB offers programmatic support for displaying error
return values.
</p>
<p>
The <a href="../api_reference/C/envstrerror.html" class="olink">db_strerror()</a> function returns a pointer to the error
message corresponding to any Berkeley DB error return, similar
to the ANSI C strerror function, but is able to handle both
system error returns and Berkeley DB specific return
values.
</p>
<p>
For example:
</p>
<a id="prog_am25"></a>
<pre class="programlisting">int ret;
...
if ((ret = dbp->put(dbp, NULL, &key, &data, 0)) != 0) {
fprintf(stderr, "put failed: %s\n", db_strerror(ret));
return (1);
}</pre>
<p>
There are also two additional error methods, <a href="../api_reference/C/dberr.html" class="olink">DB->err()</a> and
<code class="methodname">DB->errx()</code>. These methods work
like the ANSI C X3.159-1989 (ANSI C) printf function, taking a
printf-style format string and argument list, and writing a
message constructed from the format string and
arguments.
</p>
<p>
The <a href="../api_reference/C/dberr.html" class="olink">DB->err()</a> method appends the standard error string to the
constructed message; the
<code class="methodname">DB->errx()</code> method does not.
These methods provide simpler ways of displaying Berkeley DB
error messages. For example, if your application tracks
session IDs in a variable called session_id, it can include
that information in its error messages:
</p>
<p>
Error messages can additionally be configured to always
include a prefix (for example, the program name) using the
<a href="../api_reference/C/dbset_errpfx.html" class="olink">DB->set_errpfx()</a> method.
</p>
<a id="prog_am26"></a>
<pre class="programlisting">#define DATABASE "access.db"
int ret;
(void)dbp->set_errpfx(dbp, program_name);
if ((ret = dbp->open(dbp,
NULL, DATABASE, NULL, DB_BTREE, DB_CREATE, 0664)) != 0) {
dbp->err(dbp, ret, "%s", DATABASE);
dbp->errx(dbp,
"contact your system administrator: session ID was %d",
session_id);
return (1);
}</pre>
<p>
For example, if the program were called my_app and the open
call returned an EACCESS system error, the error messages
shown would appear as follows:
</p>
<pre class="programlisting">my_app: access.db: Permission denied.
my_app: contact your system administrator: session ID was 14</pre>
</div>
<div class="navfooter">
<hr />
<table width="100%" summary="Navigation footer">
<tr>
<td width="40%" align="left"><a accesskey="p" href="am_misc_perm.html">Prev</a> </td>
<td width="20%" align="center">
<a accesskey="u" href="am_misc.html">Up</a>
</td>
<td width="40%" align="right"> <a accesskey="n" href="am_misc_stability.html">Next</a></td>
</tr>
<tr>
<td width="40%" align="left" valign="top">Retrieved key/data permanence for C/C++ </td>
<td width="20%" align="center">
<a accesskey="h" href="index.html">Home</a>
</td>
<td width="40%" align="right" valign="top"> Cursor stability</td>
</tr>
</table>
</div>
</body>
</html>
|
