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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 312832 $ -->
<refentry xml:id="function.headers-sent" xmlns="http://docbook.org/ns/docbook">
<refnamediv>
<refname>headers_sent</refname>
<refpurpose>Checks if or where headers have been sent</refpurpose>
</refnamediv>
<refsect1 role="description">
&reftitle.description;
<methodsynopsis>
<type>bool</type><methodname>headers_sent</methodname>
<methodparam choice="opt"><type>string</type><parameter role="reference">file</parameter></methodparam>
<methodparam choice="opt"><type>int</type><parameter role="reference">line</parameter></methodparam>
</methodsynopsis>
<para>
Checks if or where headers have been sent.
</para>
<para>
You can't add any more header lines using the <function>header</function>
function once the header block has already been sent. Using this function
you can at least prevent getting HTTP header related error messages.
Another option is to use <link linkend="ref.outcontrol">Output Buffering</link>.
</para>
</refsect1>
<refsect1 role="parameters">
&reftitle.parameters;
<para>
<variablelist>
<varlistentry>
<term><parameter>file</parameter></term>
<listitem>
<para>
If the optional <parameter>file</parameter> and
<parameter>line</parameter> parameters are set,
<function>headers_sent</function> will put the PHP source file name
and line number where output started in the <parameter>file</parameter>
and <parameter>line</parameter> variables.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>line</parameter></term>
<listitem>
<para>
The line number where the output started.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect1>
<refsect1 role="returnvalues">
&reftitle.returnvalues;
<para>
<function>headers_sent</function> will return &false; if no HTTP headers
have already been sent or &true; otherwise.
</para>
</refsect1>
<refsect1 role="changelog">
&reftitle.changelog;
<para>
<informaltable>
<tgroup cols="2">
<thead>
<row>
<entry>&Version;</entry>
<entry>&Description;</entry>
</row>
</thead>
<tbody>
<row>
<entry>4.3.0</entry>
<entry>
The optional <parameter>file</parameter> and <parameter>line</parameter>
parameters were added.
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
</refsect1>
<refsect1 role="examples">
&reftitle.examples;
<para>
<example>
<title>Examples using <function>headers_sent</function></title>
<programlisting role="php">
<![CDATA[
<?php
// If no headers are sent, send one
if (!headers_sent()) {
header('Location: http://www.example.com/');
exit;
}
// An example using the optional file and line parameters, as of PHP 4.3.0
// Note that $filename and $linenum are passed in for later use.
// Do not assign them values beforehand.
if (!headers_sent($filename, $linenum)) {
header('Location: http://www.example.com/');
exit;
// You would most likely trigger an error here.
} else {
echo "Headers already sent in $filename on line $linenum\n" .
"Cannot redirect, for now please click this <a " .
"href=\"http://www.example.com\">link</a> instead\n";
exit;
}
?>
]]>
</programlisting>
</example>
</para>
</refsect1>
<refsect1 role="notes">
&reftitle.notes;
¬e.network.header.sapi;
</refsect1>
<refsect1 role="seealso">
&reftitle.seealso;
<para>
<simplelist>
<member><function>ob_start</function></member>
<member><function>trigger_error</function></member>
<member><function>headers_list</function></member>
<member>
<function>header</function> for a more detailed discussion of the
matters involved.
</member>
</simplelist>
</para>
</refsect1>
</refentry>
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