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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.20 $ -->
<!-- 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>bool</type><methodname>ob_start</methodname>
<methodparam choice="opt"><type>callback</type><parameter>output_callback</parameter></methodparam>
<methodparam choice="opt"><type>int</type><parameter>chunk_size</parameter></methodparam>
<methodparam choice="opt"><type>bool</type><parameter>erase</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. If the <parameter>output_callback</parameter> is not
a callable function, this function will return &false;.
If the callback function has two parameters, the second parameter is filled
with a bit-field consisting of
<constant>PHP_OUTPUT_HANDLER_START</constant>,
<constant>PHP_OUTPUT_HANDLER_CONT</constant> and
<constant>PHP_OUTPUT_HANDLER_END</constant>.
If <parameter>output_callback</parameter> returns &false; original input
is 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 its output accordingly.
</para>
</note>
<note>
<para>
Before PHP 4.3.2 this function did not return &false; in case the passed
<parameter>output_callback</parameter> can not be executed.
</para>
</note>
<warning>
<para>
Some web servers (e.g. Apache) change the working directory of a script
when calling the callback function. You can change it back by e.g.
<literal>chdir(dirname($_SERVER['SCRIPT_FILENAME']))</literal> in the
callback function.
</para>
</warning>
<para>
If the optional parameter <parameter>chunk_size</parameter> is passed, the
callback function is called on every first newline after
<parameter>chunk_size</parameter> bytes of output.
The <parameter>output_callback</parameter> parameter may be bypassed by
passing a &null; value.
</para>
<para>
If the optional parameter <parameter>erase</parameter> is set to &false;,
the buffer will not be deleted until the script finishes (as of PHP 4.3.0).
</para>
<para>
Output buffers are stackable, that is, you may call
<function>ob_start</function> while another
<function>ob_start</function> is active. Just make
sure that you call <function>ob_end_flush</function>
the appropriate number of times. If multiple output callback
functions are active, output is being filtered sequentially
through each of them in nesting order.
</para>
<para>
<function>ob_end_clean</function>,
<function>ob_end_flush</function>, <function>ob_clean</function>,
<function>ob_flush</function> and <function>ob_start</function>
may not be called from a callback function. If you call them from
callback function, the behavior is undefined. If you would like to
delete the contents of a buffer, return "" (a null string) from callback
function.
You can't even call functions using the output buffering functions like
<literal>print_r($expression, true)</literal> or
<literal>highlight_file($filename, true)</literal> from a callback
function.
</para>
<para>
<example>
<title>User defined callback function example</title>
<programlisting role="php">
<![CDATA[
<?php
function callback($buffer)
{
// replace all the apples with oranges
return (str_replace("apples", "oranges", $buffer));
}
ob_start("callback");
?>
<html>
<body>
<p>It's like comparing apples to oranges.</p>
</body>
</html>
<?php
ob_end_flush();
?>
]]>
</programlisting>
<para>
Would produce:
</para>
<screen>
<![CDATA[
<html>
<body>
<p>It's like comparing oranges to oranges.</p>
</body>
</html>
]]>
</screen>
</example>
</para>
<para>
See also <function>ob_get_contents</function>,
<function>ob_end_flush</function>,
<function>ob_end_clean</function>,
<function>ob_implicit_flush</function>,
<function>ob_gzhandler</function>, <function>ob_iconv_handler</function>
<function>mb_output_handler</function>, and
<function>ob_tidyhandler</function>.
</para>
</refsect1>
</refentry>
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