php-doc-en/reference/outcontrol/functions/ob-start.xml
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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.2 $ -->
<!-- splitted from ./en/functions/outcontrol.xml, last change in rev 1.1 -->
<refentry id="function.ob-start">
<refnamediv>
<refname>ob_start</refname>
<refpurpose>Turn on output buffering</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>void</type><methodname>ob_start</methodname>
<methodparam choice="opt"><type>string</type><parameter>
output_callback
</parameter></methodparam>
</methodsynopsis>
<para>
This function will turn output buffering on. While output
buffering is active no output is sent from the script (other than
headers), instead the output is stored in an internal buffer.
</para>
<para>
The contents of this internal buffer may be copied into a string
variable using <function>ob_get_contents</function>. To output
what is stored in the internal buffer, use
<function>ob_end_flush</function>. Alternatively,
<function>ob_end_clean</function> will silently discard the
buffer contents.
</para>
<para>
An optional <parameter>output_callback</parameter> function may
be specified. This function takes a string as a parameter and
should return a string. The function will be called when
<function>ob_end_flush</function> is called, or when the output
buffer is flushed to the browser at the end of the request. When
<parameter>output_callback</parameter> is called, it will receive
the contents of the output buffer as its parameter and is
expected to return a new output buffer as a result, which will be
sent to the browser.
</para>
<note>
<para>
In PHP 4.0.4, <function>ob_gzhandler</function> was introduced
to facilitate sending gz-encoded data to web browsers that
support compressed web pages. <function>ob_gzhandler</function>
determines what type of content encoding the browser will accept
and will return it's output accordingly.
</para>
</note>
<para>
Output buffers are stackable, that is, you may call
<function>ob_start</function> while another
<function>ob_start</function> is active. Just make
sure that you call <function>ob_end_flush</function>
the appropriate number of times. If multiple output callback
functions are active, output is being filtered sequentially
through each of them in nesting order.
</para>
<para>
<function>ob_end_clean</function>,
<function>ob_end_flush</function>, <function>ob_clean</function>,
<function>ob_flush</function> and <function>ob_start</function>
may not be called from a callback function. If you call them from
callback function, the behavior is undefined. If you would like to
delete the contents of a buffer, return "" (a null string) from callback
function.
</para>
<example>
<title>User defined callback function example</title>
<programlisting role="php">
<![CDATA[
<?php
function callback($buffer) {
// replace all the apples with oranges
return (ereg_replace("apples", "oranges", $buffer));
}
ob_start("callback");
?>
<html>
<body>
<p>It's like comparing apples to oranges.
</body>
</html>
<?php
ob_end_flush();
?>
]]>
</programlisting>
</example>
<para>
Would produce:
<informalexample>
<programlisting role="php">
<![CDATA[
<html>
<body>
<p>It's like comparing oranges to oranges.
</body>
</html>
]]>
</programlisting>
</informalexample>
</para>
<para>
See also <function>ob_get_contents</function>,
<function>ob_end_flush</function>,
<function>ob_end_clean</function>,
<function>ob_implicit_flush</function> and
<function>ob_gzhandler</function>.
</para>
</refsect1>
</refentry>
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