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<div id="projectname">lensfun
 <span id="projectnumber">0.3.2.0</span>
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<div class="title">How database files are found and loaded </div> </div>
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<div class="textblock"><p>In a typical application, all XML files are loaded automatically at startup. If the same object is defined in multiple files, later definitions override earlier definitions, e.g. user can override system-wide definitions by placing appropriately formatted XML files in its home directory.</p>
<p>A typical application will initialize the lens database by calling the method <a class="el" href="structlfDatabase.html#ac688c19eb77c64aa6f2be002f8e31e72" title="Find and load the lens database.">lfDatabase::Load()</a> with no parameters. This method searches for all available XML files and loads them, ignoring files with errors.</p>
<p>The main place where Lensfun looks for database files usually is <b>/usr/share/lensfun/version_<em>x</em></b>, where <em>x</em> is the database format version (<a class="el" href="db_versions.html">Database format versions</a>). However, this is configurable at compilation time, and for locally compiled Lensfun, it is mostly <b>/usr/local/share/lensfun/version_<em>x</em></b>. A special directory is <b>/var/lib/lensfun-updates/version_<em>x</em></b>: If it exists and contains a newer database, it is loaded instead of the main place. On Windows, this is something like <b>C:\Documents and Settings\%User%\something\version_<em>x</em></b> but I'm not sure exactly :-).</p>
<p>“Newer database” means that the file timestamp.txt, which is amongst the XML files, contains a larger value. This value is the database timestamp in UNIX time.</p>
<p>After having read the global database, the user's home directory is searched. Usually, this is <b>~/.local/share/lensfun</b>. The exact path can be found in the variable <a class="el" href="structlfDatabase.html#a447ef93e9d8d443b0f42d0ed7b837184" title="Home lens database directory (something like "~/.local/share/lensfun")">lfDatabase::HomeDataDir</a>. The subdirectory <b>updates/version_<em>x</em></b> may contain a user-specific DB update. This represents an alternative to /var/lib/lensfun-updates/version_<em>x</em> for which no root priviledges are needed.</p>
<p><b>~/.local/share/lensfun/version_<em>x</em></b> is also scanned with higher priority than the one without the version_<em>x</em>, so that the user can set entries specific for a database version. This is useful only if you need to maintain two or more different Lensfun versions on your system.</p>
<p>So sum it up for Linux and other Unix-like platforms, the load order is: </p><ol>
<li>
the directory Lensfun's database was installed into (usually /usr/share/{local/}lensfun/version_<em>x</em>), <em>or</em> /var/lib/lensfun-updates/version_<em>x</em>, <em>or</em> ~/.local/share/lensfun/updates/version_<em>x</em>, whatever is newest </li>
<li>
~/.local/share/lensfun </li>
<li>
~/.local/share/lensfun/version_<em>x</em> </li>
</ol>
<p>Another way to load database file is to load them one by one. For this you call <a class="el" href="structlfDatabase.html#a6e052ffddd1e8d927ff53a2769fa59c0" title="Load just a specific XML file.">lfDatabase::Load(const char *)</a> for every XML file that must be loaded. </p>
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