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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.16 $ -->
<!-- splitted from ./en/functions/http.xml, last change in rev 1.7 -->
<refentry id="function.headers-sent">
<refnamediv>
<refname>headers_sent</refname>
<refpurpose>Checks if or where headers have been sent</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<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>
<simpara>
<function>headers_sent</function> will return &false; if no HTTP headers
have already been sent or &true; otherwise. 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.
</simpara>
<simpara>
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>.
</simpara>
<note>
<simpara>
The optional <parameter>file</parameter> and <parameter>line</parameter>
parameters where added in PHP 4.3.0.
</simpara>
</note>
<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>
<para>
See also <function>ob_start</function>, <function>trigger_error</function>,
and <function>header</function> for a more detailed discussion of the
matters involved.
</para>
</refsect1>
</refentry>
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