<!--$Id: error.so,v 10.20 2003/10/18 19:16:00 bostic Exp $--> <!--Copyright (c) 1997,2008 Oracle. All rights reserved.--> <!--See the file LICENSE for redistribution information.--> <html> <head> <title>Berkeley DB Reference Guide: Error support</title> <meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> <meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> </head> <body bgcolor=white> <table width="100%"><tr valign=top> <td><b><dl><dt>Berkeley DB Reference Guide:<dd>Environment</dl></b></td> <td align=right><a href="../env/open.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../env/db_config.html"><img src="../../images/next.gif" alt="Next"></a> </td></tr></table> <p align=center><b>Error support</b></p> <p>Berkeley DB offers programmatic support for displaying error return values. The <a href="../../api_c/env_strerror.html">db_strerror</a> function returns a pointer to the error message corresponding to any Berkeley DB error return. This is similar to the ANSI C strerror interface, but can handle both system error returns and Berkeley DB-specific return values.</p> <p>For example:</p> <blockquote><pre>int ret; if ((ret = dbenv->set_cachesize(dbenv, 0, 32 * 1024, 1)) != 0) { fprintf(stderr, "set_cachesize failed: %s\n", db_strerror(ret)); return (1); }</pre></blockquote> <p>There are also two additional error methods: <a href="../../api_c/env_err.html">DB_ENV->err</a> and <a href="../../api_c/env_err.html">DB_ENV->errx</a>. These methods work like the 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_c/env_err.html">DB_ENV->err</a> function appends the standard error string to the constructed message; the <a href="../../api_c/env_err.html">DB_ENV->errx</a> function does not.</p> <p>Error messages can be configured always to include a prefix (for example, the program name) using the <a href="../../api_c/env_set_errpfx.html">DB_ENV->set_errpfx</a> method.</p> <p>These functions provide simpler ways of displaying Berkeley DB error messages:</p> <blockquote><pre>int ret; dbenv->set_errpfx(dbenv, program_name); if ((ret = dbenv->open(dbenv, home, DB_CREATE | DB_INIT_LOG | DB_INIT_TXN | DB_USE_ENVIRON, 0)) != 0) { dbenv->err(dbenv, ret, "open: %s", home); dbenv->errx(dbenv, "contact your system administrator: session ID was %d", session_id); return (1); }</pre></blockquote> <p>For example, if the program was called "my_app", and it tried to open an environment home directory in "/tmp/home" and the open call returned a permission error, the error messages shown would look like this:</p> <blockquote><pre>my_app: open: /tmp/home: Permission denied. my_app: contact your system administrator: session ID was 2</pre></blockquote> <table width="100%"><tr><td><br></td><td align=right><a href="../env/open.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../toc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../env/db_config.html"><img src="../../images/next.gif" alt="Next"></a> </td></tr></table> <p><font size=1>Copyright (c) 1996,2008 Oracle. All rights reserved.</font> </body> </html>