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<a href="../c3ref/intro.html"><h2>SQLite C Interface</h2></a>
<h2>Query Progress Callbacks</h2>
</div>
<blockquote><pre>
void sqlite3_progress_handler(sqlite3*, int, int(*)(void*), void*);
</pre></blockquote>
<p>
The sqlite3_progress_handler(D,N,X,P) interface causes the callback
function X to be invoked periodically during long running calls to
<a href="../c3ref/step.html">sqlite3_step()</a> and <a href="../c3ref/prepare.html">sqlite3_prepare()</a> and similar for
database connection D. An example use for this
interface is to keep a GUI updated during a large query.</p>
<p>The parameter P is passed through as the only parameter to the
callback function X. The parameter N is the approximate number of
<a href="../opcode.html">virtual machine instructions</a> that are evaluated between successive
invocations of the callback X. If N is less than one then the progress
handler is disabled.</p>
<p>Only a single progress handler may be defined at one time per
<a href="../c3ref/sqlite3.html">database connection</a>; setting a new progress handler cancels the
old one. Setting parameter X to NULL disables the progress handler.
The progress handler is also disabled by setting N to a value less
than 1.</p>
<p>If the progress callback returns non-zero, the operation is
interrupted. This feature can be used to implement a
"Cancel" button on a GUI progress dialog box.</p>
<p>The progress handler callback must not do anything that will modify
the database connection that invoked the progress handler.
Note that <a href="../c3ref/prepare.html">sqlite3_prepare_v2()</a> and <a href="../c3ref/step.html">sqlite3_step()</a> both modify their
database connections for the meaning of "modify" in this paragraph.</p>
<p>The progress handler callback would originally only be invoked from the
bytecode engine. It still might be invoked during <a href="../c3ref/prepare.html">sqlite3_prepare()</a>
and similar because those routines might force a reparse of the schema
which involves running the bytecode engine. However, beginning with
SQLite version 3.41.0, the progress handler callback might also be
invoked directly from <a href="../c3ref/prepare.html">sqlite3_prepare()</a> while analyzing and generating
code for complex queries.
</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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