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<h1 class="title">Introduction</h1>
<p class="para">
The Output Control functions allow you to control when output is
sent from the script. This can be useful in several different
situations, especially if you need to send headers to the browser
after your script has began outputting data. The Output Control
functions do not affect headers sent using
<span class="function"><a href="function.header.html" class="function">header()</a></span> or <span class="function"><a href="function.setcookie.html" class="function">setcookie()</a></span>,
only functions such as <span class="function"><a href="function.echo.html" class="function">echo</a></span> and data between
blocks of PHP code.
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<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
When upgrading from PHP 4.1.x (and 4.2.x) to 4.3.x due to a bug in
earlier versions you must ensure that
<em>implicit_flush</em> is <em>OFF</em> in
your <var class="filename">php.ini</var>, otherwise any output with
<span class="function"><a href="function.ob-start.html" class="function">ob_start()</a></span> will not be hidden from output.
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