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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.4 $ -->
<!-- splitted from ./en/functions/funchand.xml, last change in rev 1.1 -->
<refentry id="function.function-exists">
<refnamediv>
<refname>function_exists</refname>
<refpurpose>
Return &true; if the given function has been defined
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<methodsynopsis>
<type>bool</type><methodname>function_exists</methodname>
<methodparam><type>string</type><parameter>function_name</parameter></methodparam>
</methodsynopsis>
<para>
Checks the list of defined functions, both built-in (internal) and
user-defined, for <parameter>function_name</parameter>. &return.success;
</para>
<para>
<informalexample>
<programlisting role="php">
<![CDATA[
<?php
if (function_exists('imap_open')) {
echo "IMAP functions are available.<br />\n";
} else {
echo "IMAP functions are not available.<br />\n";
}
?>
]]>
</programlisting>
</informalexample>
</para>
<para>
Note that a function name may exist even if the function itself
is unusable due to configuration or compiling options (with the
<link linkend="ref.image">image</link> functions being an example).
Also note that <function>function_exists</function> will return
&false; for constructs, such as <function>include_once</function>
and <function>echo</function>.
</para>
<para>
See also <function>method_exists</function>,
<function>is_callable</function> and
<function>get_defined_functions</function>.
</para>
</refsect1>
</refentry>
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