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+<a href="../c3ref/intro.html"><h2>SQLite C Interface</h2></a>
+<h2>Obtain Aggregate Function Context</h2>
+</div>
+<blockquote><pre>
+void *sqlite3_aggregate_context(sqlite3_context*, int nBytes);
+</pre></blockquote>
+<p>
+Implementations of aggregate SQL functions use this
+routine to allocate memory for storing their state.</p>
+
+<p>The first time the sqlite3_aggregate_context(C,N) routine is called
+for a particular aggregate function, SQLite allocates
+N bytes of memory, zeroes out that memory, and returns a pointer
+to the new memory. On second and subsequent calls to
+sqlite3_aggregate_context() for the same aggregate function instance,
+the same buffer is returned.  Sqlite3_aggregate_context() is normally
+called once for each invocation of the xStep callback and then one
+last time when the xFinal callback is invoked.  When no rows match
+an aggregate query, the xStep() callback of the aggregate function
+implementation is never called and xFinal() is called exactly once.
+In those cases, sqlite3_aggregate_context() might be called for the
+first time from within xFinal().</p>
+
+<p>The sqlite3_aggregate_context(C,N) routine returns a NULL pointer
+when first called if N is less than or equal to zero or if a memory
+allocation error occurs.</p>
+
+<p>The amount of space allocated by sqlite3_aggregate_context(C,N) is
+determined by the N parameter on first successful call.  Changing the
+value of N in any subsequent call to sqlite3_aggregate_context() within
+the same aggregate function instance will not resize the memory
+allocation.  Within the xFinal callback, it is customary to set
+N=0 in calls to sqlite3_aggregate_context(C,N) so that no
+pointless memory allocations occur.</p>
+
+<p>SQLite automatically frees the memory allocated by
+sqlite3_aggregate_context() when the aggregate query concludes.</p>
+
+<p>The first parameter must be a copy of the
+<a href="../c3ref/context.html">SQL function context</a> that is the first parameter
+to the xStep or xFinal callback routine that implements the aggregate
+function.</p>
+
+<p>This routine must be called from the same thread in which
+the aggregate SQL function is running.
+</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>
+