1<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml"> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <title>Error Returns</title> 7 <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> 8 <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /> 9 <link rel="start" href="index.html" title="Getting Started with Berkeley DB" /> 10 <link rel="up" href="introduction.html" title="Chapter��1.��Introduction to Berkeley DB" /> 11 <link rel="prev" href="environments.html" title="Environments" /> 12 <link rel="next" href="gettingit.html" title="Getting and Using DB" /> 13 </head> 14 <body> 15 <div class="navheader"> 16 <table width="100%" summary="Navigation header"> 17 <tr> 18 <th colspan="3" align="center">Error Returns</th> 19 </tr> 20 <tr> 21 <td width="20%" align="left"><a accesskey="p" href="environments.html">Prev</a>��</td> 22 <th width="60%" align="center">Chapter��1.��Introduction to Berkeley DB </th> 23 <td width="20%" align="right">��<a accesskey="n" href="gettingit.html">Next</a></td> 24 </tr> 25 </table> 26 <hr /> 27 </div> 28 <div class="sect1" lang="en" xml:lang="en"> 29 <div class="titlepage"> 30 <div> 31 <div> 32 <h2 class="title" style="clear: both"><a id="returns"></a>Error Returns</h2> 33 </div> 34 </div> 35 </div> 36 <p> 37 Before continuing, it is useful to spend a few moments on error returns 38 in DB. 39 </p> 40 <p> 41 42 <span>The</span> 43 DB interfaces always return a value of 0 on success. If the 44 operation does not succeed for any reason, the return value will be 45 non-zero. 46 </p> 47 <p> 48 If a system error occurred (for example, DB ran out of disk 49 space, or permission to access a file was denied, or an illegal argument 50 was specified to one of the interfaces), DB returns an 51 <code class="literal">errno</code> 52 value. All of the possible values of <code class="literal">errno</code> are greater than 0. 53 </p> 54 <p> 55 If the operation did not fail due to a system error, but was not 56 successful either, DB returns a special error value. For 57 example, if you tried to retrieve data from the database and the 58 record for which you are searching does not exist, DB would return 59 <code class="literal">DB_NOTFOUND</code>, a special error value that means the requested 60 key does not appear in the database. All of the possible special error 61 values are less than 0. 62 </p> 63 <p> 64 DB also offers programmatic support for displaying error return 65 values. First, the <code class="function">db_strerror</code> function returns 66 a pointer to the error 67 message corresponding to any DB error return, similar to the 68 ANSI C <code class="function">strerror</code> function, but is able to handle 69 both system error returns and DB-specific return values. 70 </p> 71 <p> 72 Second, there are two error functions, 73 <code class="methodname">DB->err</code> and <code class="methodname">DB->errx</code>. 74 These functions work like the ANSI C <code class="function">printf</code> function, 75 taking a printf-style format string and argument list, and optionally 76 appending the standard error string to a message constructed from 77 the format string and other arguments. 78 </p> 79 </div> 80 <div class="navfooter"> 81 <hr /> 82 <table width="100%" summary="Navigation footer"> 83 <tr> 84 <td width="40%" align="left"><a accesskey="p" href="environments.html">Prev</a>��</td> 85 <td width="20%" align="center"> 86 <a accesskey="u" href="introduction.html">Up</a> 87 </td> 88 <td width="40%" align="right">��<a accesskey="n" href="gettingit.html">Next</a></td> 89 </tr> 90 <tr> 91 <td width="40%" align="left" valign="top">Environments��</td> 92 <td width="20%" align="center"> 93 <a accesskey="h" href="index.html">Home</a> 94 </td> 95 <td width="40%" align="right" valign="top">��Getting and Using DB </td> 96 </tr> 97 </table> 98 </div> 99 </body> 100</html> 101