mirror of
https://github.com/sigmasternchen/php-doc-en
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302 lines
9.8 KiB
XML
302 lines
9.8 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<refentry xml:id="function.ob-start" xmlns="http://docbook.org/ns/docbook">
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<refnamediv>
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<refname>ob_start</refname>
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<refpurpose>Turn on output buffering</refpurpose>
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</refnamediv>
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<refsect1 role="description">
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&reftitle.description;
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<methodsynopsis>
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<type>bool</type><methodname>ob_start</methodname>
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<methodparam choice="opt"><type>callable</type><parameter>callback</parameter><initializer>&null;</initializer></methodparam>
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<methodparam choice="opt"><type>int</type><parameter>chunk_size</parameter><initializer>0</initializer></methodparam>
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<methodparam choice="opt"><type>int</type><parameter>flags</parameter><initializer><constant>PHP_OUTPUT_HANDLER_STDFLAGS</constant></initializer></methodparam>
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</methodsynopsis>
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<para>
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This function will turn output buffering on. While output buffering is
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active no output is sent from the script (other than headers), instead the
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output is stored in an internal buffer.
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</para>
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<para>
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The contents of this internal buffer may be copied into a string variable
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using <function>ob_get_contents</function>. To output what is stored in
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the internal buffer, use <function>ob_end_flush</function>. Alternatively,
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<function>ob_end_clean</function> will silently discard the buffer
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contents.
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</para>
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<warning>
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<para>
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Some web servers (e.g. Apache) change the working directory of a script
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when calling the callback function. You can change it back by e.g.
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<literal>chdir(dirname($_SERVER['SCRIPT_FILENAME']))</literal> in the
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callback function.
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</para>
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</warning>
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<para>
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Output buffers are stackable, that is, you may call
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<function>ob_start</function> while another
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<function>ob_start</function> is active. Just make
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sure that you call <function>ob_end_flush</function>
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the appropriate number of times. If multiple output callback
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functions are active, output is being filtered sequentially
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through each of them in nesting order.
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</para>
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<para>
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If output buffering is still active when the script ends, PHP outputs the
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contents automatically.
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</para>
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</refsect1>
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<refsect1 role="parameters">
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&reftitle.parameters;
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<para>
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<variablelist>
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<varlistentry>
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<term><parameter>callback</parameter></term>
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<listitem>
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<para>
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An optional <parameter>callback</parameter> function may be
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specified. This function takes a string as a parameter and should
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return a string. The function will be called when
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the output buffer is flushed (sent) or cleaned (with
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<function>ob_flush</function>, <function>ob_clean</function> or similar
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function) or when the output buffer
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is flushed to the browser at the end of the request. When
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<parameter>callback</parameter> is called, it will receive the
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contents of the output buffer as its parameter and is expected to
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return a new output buffer as a result, which will be sent to the
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browser. If the <parameter>callback</parameter> is not a
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callable function, this function will return &false;.
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This is the callback signature:
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</para>
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<para>
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<methodsynopsis>
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<type>string</type><methodname><replaceable>handler</replaceable></methodname>
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<methodparam><type>string</type><parameter>buffer</parameter></methodparam>
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<methodparam choice="opt"><type>int</type><parameter>phase</parameter></methodparam>
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</methodsynopsis>
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<variablelist>
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<varlistentry>
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<term><parameter>buffer</parameter></term>
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<listitem>
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<simpara>
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Contents of the output buffer.
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</simpara>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>phase</parameter></term>
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<listitem>
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<simpara>
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Bitmask of <link linkend="outcontrol.constants"><constant>PHP_OUTPUT_HANDLER_*</constant> constants</link>.
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</simpara>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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<para>
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If <parameter>callback</parameter> returns &false; original
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input is sent to the browser.
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</para>
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<para>
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The <parameter>callback</parameter> parameter may be bypassed
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by passing a &null; value.
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</para>
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<para>
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<function>ob_end_clean</function>, <function>ob_end_flush</function>,
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<function>ob_clean</function>, <function>ob_flush</function> and
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<function>ob_start</function> may not be called from a callback
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function. If you call them from callback function, the behavior is
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undefined. If you would like to delete the contents of a buffer,
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return "" (a null string) from callback function.
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You can't even call functions using the output buffering functions like
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<literal>print_r($expression, true)</literal> or
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<literal>highlight_file($filename, true)</literal> from a callback
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function.
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</para>
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<note>
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<para>
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<function>ob_gzhandler</function> function exists to
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facilitate sending gz-encoded data to web browsers that support
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compressed web pages. <function>ob_gzhandler</function> determines
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what type of content encoding the browser will accept and will return
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its output accordingly.
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</para>
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</note>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>chunk_size</parameter></term>
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<listitem>
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<para>
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If the optional parameter <parameter>chunk_size</parameter> is passed, the
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buffer will be flushed after any output call which causes the buffer's
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length to equal or exceed <parameter>chunk_size</parameter>. The default
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value <literal>0</literal> means that the output function will only be
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called when the output buffer is closed.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>flags</parameter></term>
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<listitem>
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<para>
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The <parameter>flags</parameter> parameter is a bitmask that controls
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the operations that can be performed on the output buffer. The default
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is to allow output buffers to be cleaned, flushed and removed, which
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can be set explicitly via
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<constant>PHP_OUTPUT_HANDLER_CLEANABLE</constant> |
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<constant>PHP_OUTPUT_HANDLER_FLUSHABLE</constant> |
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<constant>PHP_OUTPUT_HANDLER_REMOVABLE</constant>, or
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<constant>PHP_OUTPUT_HANDLER_STDFLAGS</constant> as shorthand.
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</para>
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<para>
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Each flag controls access to a set of functions, as described below:
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<informaltable>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>Constant</entry>
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<entry>Functions</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><constant>PHP_OUTPUT_HANDLER_CLEANABLE</constant></entry>
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<entry>
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<function>ob_clean</function>,
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<function>ob_end_clean</function>, and
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<function>ob_get_clean</function>.
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</entry>
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</row>
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<row>
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<entry><constant>PHP_OUTPUT_HANDLER_FLUSHABLE</constant></entry>
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<entry>
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<function>ob_end_flush</function>,
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<function>ob_flush</function>, and
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<function>ob_get_flush</function>.
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</entry>
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</row>
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<row>
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<entry><constant>PHP_OUTPUT_HANDLER_REMOVABLE</constant></entry>
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<entry>
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<function>ob_end_clean</function>,
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<function>ob_end_flush</function>, and
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<function>ob_get_flush</function>.
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</entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect1>
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<refsect1 role="returnvalues">
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&reftitle.returnvalues;
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<para>
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&return.success;
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</para>
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</refsect1>
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<refsect1 role="examples">
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&reftitle.examples;
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<para>
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<example>
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<title>User defined callback function example</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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function callback($buffer)
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{
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// replace all the apples with oranges
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return (str_replace("apples", "oranges", $buffer));
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}
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ob_start("callback");
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?>
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<html>
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<body>
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<p>It's like comparing apples to oranges.</p>
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</body>
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</html>
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<?php
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ob_end_flush();
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?>
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]]>
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</programlisting>
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&example.outputs;
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<screen>
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<![CDATA[
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<html>
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<body>
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<p>It's like comparing oranges to oranges.</p>
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</body>
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</html>
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]]>
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</screen>
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</example>
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</para>
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<para>
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<example xml:id="function.ob-start.flags-bc">
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<title>Creating an unerasable output buffer</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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ob_start(null, 0, PHP_OUTPUT_HANDLER_STDFLAGS ^ PHP_OUTPUT_HANDLER_REMOVABLE);
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?>
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]]>
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</programlisting>
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</example>
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</para>
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</refsect1>
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<refsect1 role="seealso">
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&reftitle.seealso;
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<para>
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<simplelist>
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<member><function>ob_get_contents</function></member>
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<member><function>ob_end_clean</function></member>
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<member><function>ob_end_flush</function></member>
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<member><function>ob_implicit_flush</function></member>
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<member><function>ob_gzhandler</function></member>
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<member><function>ob_iconv_handler</function></member>
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<member><function>mb_output_handler</function></member>
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<member><function>ob_tidyhandler</function></member>
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</simplelist>
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</para>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"~/.phpdoc/manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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