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<a href="../c3ref/intro.html"><h2>SQLite C Interface</h2></a>
<h2>Virtual Table Instance Object</h2>
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<blockquote><pre>
struct sqlite3_vtab {
const sqlite3_module *pModule; /* The module for this virtual table */
int nRef; /* Number of open cursors */
char *zErrMsg; /* Error message from sqlite3_mprintf() */
/* Virtual table implementations will typically add additional fields */
};
</pre></blockquote>
<p>
Every <a href="../c3ref/module.html">virtual table module</a> implementation uses a subclass
of this object to describe a particular instance
of the <a href="../vtab.html">virtual table</a>. Each subclass will
be tailored to the specific needs of the module implementation.
The purpose of this superclass is to define certain fields that are
common to all module implementations.</p>
<p>Virtual tables methods can set an error message by assigning a
string obtained from <a href="../c3ref/mprintf.html">sqlite3_mprintf()</a> to zErrMsg. The method should
take care that any prior string is freed by a call to <a href="../c3ref/free.html">sqlite3_free()</a>
prior to assigning a new string to zErrMsg. After the error message
is delivered up to the client application, the string will be automatically
freed by sqlite3_free() and the zErrMsg field will be zeroed.
</p><p>See also lists of
<a href="../c3ref/objlist.html">Objects</a>,
<a href="../c3ref/constlist.html">Constants</a>, and
<a href="../c3ref/funclist.html">Functions</a>.</p>
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