<?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 class="navheader"> <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> <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> <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>