php-doc-en/reference/classobj/functions/class-exists.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.class-exists" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>class_exists</refname>
  <refpurpose>Checks if the class has been defined</refpurpose>
 </refnamediv>
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>bool</type><methodname>class_exists</methodname>
   <methodparam><type>string</type><parameter>class_name</parameter></methodparam>
   <methodparam choice="opt"><type>bool</type><parameter>autoload</parameter><initializer>true</initializer></methodparam>
  </methodsynopsis>
  <para>
   This function checks whether or not the given class has been defined.
  </para>
 </refsect1>
 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>class_name</parameter></term>
     <listitem>
      <para>
       The class name. The name is matched in a case-insensitive manner.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>autoload</parameter></term>
     <listitem>
      <para>
       Whether or not to call &link.autoload; by default.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>
 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns &true; if <parameter>class_name</parameter> is a defined class,
   &false; 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>5.0.2</entry>
       <entry>
        No longer returns &true; for defined interfaces. Use
        <function>interface_exists</function>.
       </entry>
      </row>
      <row>
       <entry>5.0.0</entry>
       <entry>
        The <parameter>autoload</parameter> parameter was added.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>
 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>class_exists</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
// Check that the class exists before trying to use it
if (class_exists('MyClass')) {
    $myclass = new MyClass();
}

?>
]]>
    </programlisting>
   </example>
   <example>
    <title><parameter>autoload</parameter> parameter example</title>
    <programlisting role="php">
<![CDATA[
<?php
function __autoload($class)
{
    include($class . '.php');

    // Check to see whether the include declared the class
    if (!class_exists($class, false)) {
        trigger_error("Unable to load class: $class", E_USER_WARNING);
    }
}

if (class_exists('MyClass')) {
    $myclass = new MyClass();
}

?>
]]>
    </programlisting>
   </example>
  </para>
 </refsect1>
 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>function_exists</function></member>
    <member><function>interface_exists</function></member>
    <member><function>get_declared_classes</function></member>
   </simplelist>
  </para>
 </refsect1>
</refentry>

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