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<refentry xml:id="function.unserialize" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>unserialize</refname>
  <refpurpose>
   Creates a PHP value from a stored representation
  </refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>mixed</type><methodname>unserialize</methodname>
   <methodparam><type>string</type><parameter>data</parameter></methodparam>
   <methodparam choice="opt"><type>array</type><parameter>options</parameter><initializer>[]</initializer></methodparam>
  </methodsynopsis>
  <simpara>
   <function>unserialize</function> takes a single serialized variable and
   converts it back into a PHP value.
  </simpara>
  <warning>
   <para>
    Do not pass untrusted user input to <function>unserialize</function> regardless
    of the <parameter>options</parameter> value of <literal>allowed_classes</literal>.
    Unserialization can result in code being loaded and executed due to object
    instantiation and autoloading, and a malicious user may be able to exploit
    this. Use a safe, standard data interchange format such as JSON (via
    <function>json_decode</function> and <function>json_encode</function>) if
    you need to pass serialized data to the user.
   </para>
   <para>
    If you need to unserialize externally-stored serialized data, consider using
    <function>hash_hmac</function> for data validation. Make sure data is
    not modified by anyone but you.
   </para>
  </warning>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>data</parameter></term>
     <listitem>
      <para>
       The serialized string.
      </para>
      <para>
       If the variable being unserialized is an object, after successfully
       reconstructing the object PHP will automatically attempt to call the
       <link linkend="object.unserialize">__unserialize()</link> or <link linkend="object.wakeup">__wakeup()</link> methods (if one exists).
      </para>
      <para>
       <note>
        <title>
         <link linkend="ini.unserialize-callback-func">unserialize_callback_func</link>
          directive
        </title>
        <para>
         The callback specified in the
         <link linkend="ini.unserialize-callback-func">unserialize_callback_func</link>
         directive is called when an undefined class is unserialized.
         If no callback is specified, the object will be instantiated as
         <classname>__PHP_Incomplete_Class</classname>.
        </para>
       </note>
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>options</parameter></term>
     <listitem>
      <para>
       Any options to be provided to <function>unserialize</function>, as an
       associative array.
      </para>
      <table>
       <title>Valid options</title>
       <tgroup cols="3">
        <thead>
         <row>
          <entry>Name</entry>
          <entry>Type</entry>
          <entry>Description</entry>
         </row>
        </thead>
        <tbody>
         <row>
          <entry><literal>allowed_classes</literal></entry>
          <entry><type>mixed</type></entry>
          <entry>
           <simpara>
            Either an <type>array</type> of class names which should be
            accepted, &false; to accept no classes, or &true; to accept all
            classes. If this option is defined and
            <function>unserialize</function> encounters an object of a class
            that isn't to be accepted, then the object will be instantiated as
            <classname>__PHP_Incomplete_Class</classname> instead.
           </simpara>
           <simpara>
            Omitting this option is the same as defining it as &true;: PHP
            will attempt to instantiate objects of any class.
           </simpara>
          </entry>
         </row>
         <row>
          <entry><literal>max_depth</literal></entry>
          <entry><type>int</type></entry>
          <entry>
           <simpara>
            The maximum depth of structures permitted during unserialization,
            and is intended to prevent stack overflows. The default depth limit
            is <literal>4096</literal> and can be disabled by setting
            <literal>max_depth</literal> to <literal>0</literal>.
           </simpara>
          </entry>
         </row>
        </tbody>
       </tgroup>
      </table>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   The converted value is returned, and can be a <type>bool</type>,
   <type>int</type>, <type>float</type>, <type>string</type>,
   <type>array</type> or <type>object</type>.
  </para>
  <para>
   In case the passed string is not unserializeable, &false; is returned and
   <constant>E_WARNING</constant> is issued.
  </para>
 </refsect1>

 <refsect1 role="errors">
  &reftitle.errors;
  <para>
   Objects may throw <classname>Throwable</classname>s in their unserialization handlers.
  </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>8.3.0</entry>
       <entry>
        Now emits <constant>E_WARNING</constant> when the input string has unconsumed data.
       </entry>
      </row>
      <row>
       <entry>8.3.0</entry>
       <entry>
        Now emits <constant>E_WARNING</constant> when the passed string is not unserializeable;
        previously <constant>E_NOTICE</constant> was emitted.
       </entry>
      </row>
      <row>
       <entry>7.4.0</entry>
       <entry>
        Added the <literal>max_depth</literal> element of
        <parameter>options</parameter> to set the maximum depth of structures permitted during unserialization.
       </entry>
      </row>
      <row>
       <entry>7.1.0</entry>
       <entry>
        The <literal>allowed_classes</literal> element of
        <parameter>options</parameter>) is now strictly typed, i.e. if anything
        other than an <type>array</type> or a <type>bool</type> is given,
        <function>unserialize</function> returns &false; and issues an
        <constant>E_WARNING</constant>.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>unserialize</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
// Here, we use unserialize() to load session data to the
// $session_data array from the string selected from a database.
// This example complements the one described with serialize().

$conn = odbc_connect("webdb", "php", "chicken");
$stmt = odbc_prepare($conn, "SELECT data FROM sessions WHERE id = ?");
$sqldata = array($_SERVER['PHP_AUTH_USER']);
if (!odbc_execute($stmt, $sqldata) || !odbc_fetch_into($stmt, $tmp)) {
    // if the execute or fetch fails, initialize to empty array
    $session_data = array();
} else {
    // we should now have the serialized data in $tmp[0].
    $session_data = unserialize($tmp[0]);
    if (!is_array($session_data)) {
        // something went wrong, initialize to empty array
        $session_data = array();
    }
}
?>
]]>
    </programlisting>
   </example>
  </para>
  <para>
   <example>
    <title>unserialize_callback_func example</title>
    <programlisting role="php">
<![CDATA[
<?php
$serialized_object='O:1:"a":1:{s:5:"value";s:3:"100";}';

ini_set('unserialize_callback_func', 'mycallback'); // set your callback_function

function mycallback($classname)
{
    // just include a file containing your class definition
    // you get $classname to figure out which class definition is required
}
?>
]]>
    </programlisting>
   </example>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;
  <warning>
   <para>
    &false; is returned both in the case of an error and if unserializing
    the serialized &false; value. It is possible to catch this special case by
    comparing <parameter>data</parameter> with
    <literal>serialize(false)</literal> or by catching the issued
    <constant>E_NOTICE</constant>.
   </para>
  </warning>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>json_encode</function></member>
    <member><function>json_decode</function></member>
    <member><function>hash_hmac</function></member>
    <member><function>serialize</function></member>
    <member><link linkend="language.oop5.autoload">Autoloading Classes</link></member>
    <member><link linkend="ini.unserialize-callback-func">unserialize_callback_func</link></member>
    <member><link linkend="ini.unserialize-max-depth">unserialize_max_depth</link></member>
    <member><link linkend="object.wakeup">__wakeup()</link></member>
    <member><link linkend="object.serialize">__serialize()</link></member>
    <member><link linkend="object.unserialize">__unserialize()</link></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>
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