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//proc/self/root/usr/share/doc/db4-devel-4.7.25/gsg/C/returns.html
<?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 Returns</title> <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> <meta name="generator" content="DocBook XSL Stylesheets V1.62.4" /> <link rel="home" href="index.html" title="Getting Started with Berkeley DB" /> <link rel="up" href="introduction.html" title="Chapter 1. Introduction to Berkeley DB " /> <link rel="previous" href="environments.html" title="Environments" /> <link rel="next" href="gettingit.html" title="Getting and Using DB " /> </head> <body> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">Error Returns</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="environments.html">Prev</a> </td> <th width="60%" align="center">Chapter 1. Introduction to Berkeley DB </th> <td width="20%" align="right"> <a accesskey="n" href="gettingit.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="returns"></a>Error Returns</h2> </div> </div> <div></div> </div> <p> Before continuing, it is useful to spend a few moments on error returns in DB. </p> <p> <span>The</span> DB interfaces always return a value of 0 on success. If the operation does not succeed for any reason, the return value will be non-zero. </p> <p> If a system error occurred (for example, DB ran out of disk space, or permission to access a file was denied, or an illegal argument was specified to one of the interfaces), DB returns an <tt class="literal">errno</tt> value. All of the possible values of <tt class="literal">errno</tt> are greater than 0. </p> <p> If the operation did not fail due to a system error, but was not successful either, DB returns a special error value. For example, if you tried to retrieve data from the database and the record for which you are searching does not exist, DB would return <tt class="literal">DB_NOTFOUND</tt>, a special error value that means the requested key does not appear in the database. All of the possible special error values are less than 0. </p> <p> DB also offers programmatic support for displaying error return values. First, the <tt class="function">db_strerror</tt> function returns a pointer to the error message corresponding to any DB error return, similar to the ANSI C <tt class="function">strerror</tt> function, but is able to handle both system error returns and DB-specific return values. </p> <p> Second, there are two error functions, <tt class="methodname">DB->err</tt> and <tt class="methodname">DB->errx</tt>. These functions work like the ANSI C <tt class="function">printf</tt> function, taking a printf-style format string and argument list, and optionally appending the standard error string to a message constructed from the format string and other arguments. </p> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="environments.html">Prev</a> </td> <td width="20%" align="center"> <a accesskey="u" href="introduction.html">Up</a> </td> <td width="40%" align="right"> <a accesskey="n" href="gettingit.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">Environments </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> Getting and Using DB </td> </tr> </table> </div> </body> </html>
