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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html><head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<title>Query Progress Callbacks</title>
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<a href="intro.html"><h2>SQLite C Interface</h2></a><h2>Query Progress Callbacks</h2><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/exec.html">sqlite3_exec()</a>, <a href="../c3ref/step.html">sqlite3_step()</a> and <a href="../c3ref/free_table.html">sqlite3_get_table()</a> 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></p><p>See also lists of
  <a href="objlist.html">Objects</a>,
  <a href="constlist.html">Constants</a>, and
  <a href="funclist.html">Functions</a>.</p>