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+<!-- keywords: sqlite3_get_auxdata sqlite3_set_auxdata -->
+<div class=nosearch>
+<a href="../c3ref/intro.html"><h2>SQLite C Interface</h2></a>
+<h2>Function Auxiliary Data</h2>
+</div>
+<blockquote><pre>
+void *sqlite3_get_auxdata(sqlite3_context*, int N);
+void sqlite3_set_auxdata(sqlite3_context*, int N, void*, void (*)(void*));
+</pre></blockquote>
+<p>
+These functions may be used by (non-aggregate) SQL functions to
+associate auxiliary data with argument values. If the same argument
+value is passed to multiple invocations of the same SQL function during
+query execution, under some circumstances the associated auxiliary data
+might be preserved. An example of where this might be useful is in a
+regular-expression matching function. The compiled version of the regular
+expression can be stored as auxiliary data associated with the pattern string.
+Then as long as the pattern string remains the same,
+the compiled regular expression can be reused on multiple
+invocations of the same function.</p>
+
+<p>The sqlite3_get_auxdata(C,N) interface returns a pointer to the auxiliary data
+associated by the sqlite3_set_auxdata(C,N,P,X) function with the Nth argument
+value to the application-defined function. N is zero for the left-most
+function argument. If there is no auxiliary data
+associated with the function argument, the sqlite3_get_auxdata(C,N) interface
+returns a NULL pointer.</p>
+
+<p>The sqlite3_set_auxdata(C,N,P,X) interface saves P as auxiliary data for the
+N-th argument of the application-defined function. Subsequent
+calls to sqlite3_get_auxdata(C,N) return P from the most recent
+sqlite3_set_auxdata(C,N,P,X) call if the auxiliary data is still valid or
+NULL if the auxiliary data has been discarded.
+After each call to sqlite3_set_auxdata(C,N,P,X) where X is not NULL,
+SQLite will invoke the destructor function X with parameter P exactly
+once, when the auxiliary data is discarded.
+SQLite is free to discard the auxiliary data at any time, including: <ul>
+<li> when the corresponding function parameter changes, or
+<li> when <a href="../c3ref/reset.html">sqlite3_reset()</a> or <a href="../c3ref/finalize.html">sqlite3_finalize()</a> is called for the
+SQL statement, or
+<li> when sqlite3_set_auxdata() is invoked again on the same
+parameter, or
+<li> during the original sqlite3_set_auxdata() call when a memory
+allocation error occurs.
+<li> during the original sqlite3_set_auxdata() call if the function
+is evaluated during query planning instead of during query execution,
+as sometimes happens with <a href="../compile.html#enable_stat4">SQLITE_ENABLE_STAT4</a>. </ul></p>
+
+<p>Note the last two bullets in particular. The destructor X in
+sqlite3_set_auxdata(C,N,P,X) might be called immediately, before the
+sqlite3_set_auxdata() interface even returns. Hence sqlite3_set_auxdata()
+should be called near the end of the function implementation and the
+function implementation should not make any use of P after
+sqlite3_set_auxdata() has been called. Furthermore, a call to
+sqlite3_get_auxdata() that occurs immediately after a corresponding call
+to sqlite3_set_auxdata() might still return NULL if an out-of-memory
+condition occurred during the sqlite3_set_auxdata() call or if the
+function is being evaluated during query planning rather than during
+query execution.</p>
+
+<p>In practice, auxiliary data is preserved between function calls for
+function parameters that are compile-time constants, including literal
+values and <a href="../lang_expr.html#varparam">parameters</a> and expressions composed from the same.</p>
+
+<p>The value of the N parameter to these interfaces should be non-negative.
+Future enhancements may make use of negative N values to define new
+kinds of function caching behavior.</p>
+
+<p>These routines must be called from the same thread in which
+the SQL function is running.</p>
+
+<p>See also: <a href="../c3ref/get_clientdata.html">sqlite3_get_clientdata()</a> and <a href="../c3ref/get_clientdata.html">sqlite3_set_clientdata()</a>.
+</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>
+