php-doc-en/reference/var/functions/empty.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
<refentry xml:id="function.empty" xmlns="http://docbook.org/ns/docbook">
 <refnamediv>
  <refname>empty</refname>
  <refpurpose>Determine whether a variable is empty</refpurpose>
 </refnamediv>
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>bool</type><methodname>empty</methodname>
   <methodparam><type>mixed</type><parameter>var</parameter></methodparam>
  </methodsynopsis>
  <para>
   Determine whether a variable is considered to be empty. A variable is considered empty if it does not exist or if its value equals &false;. <function>empty</function> does not generate a warning if the variable does not exist.
  </para>
 </refsect1>
 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>var</parameter></term>
     <listitem>
      <para>
       Variable to be checked
      </para>
      <note>
       <para>
        <function>empty</function> only checks variables as anything else will
        result in a parse error. In other words, the following will not work:
        <command>empty(trim($name))</command>. Instead, use
        <command>trim($name) == false</command>.
       </para>
      </note>
      <para>
       No warning is generated if the variable does not exist.
       That means <function>empty</function> is essentially the
       concise equivalent to <command>!isset($var) || $var == false</command>.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>
 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns &false; if <parameter>var</parameter> exists and has a non-empty, non-zero value.
   Otherwise returns &true;.
  </para>
  <para>
   The following things are considered to be empty:
   <simplelist>
    <member><literal>""</literal> (an empty string)</member>
    <member><literal>0</literal> (0 as an integer)</member>
    <member><literal>0.0</literal> (0 as a float)</member>
    <member><literal>"0"</literal> (0 as a string)</member>
    <member>&null;</member>
    <member>&false;</member>
    <member><literal>array()</literal> (an empty array)</member>
    <member><literal>$var;</literal> (a variable declared, but without a value)</member>
   </simplelist>
  </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>5.4.0</entry>
       <entry>
        <para>
         Checking non-numeric offsets of strings returns &true;.
        </para>
       </entry>
      </row>
      <row>
       <entry>5.0.0</entry>
       <entry>
        <para>
         Objects with no properties are no longer considered empty.
        </para>
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>
 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title>
     A simple <function>empty</function> / <function>isset</function>
     comparison.
    </title>  
    <programlisting role="php">
<![CDATA[
<?php
$var = 0;

// Evaluates to true because $var is empty
if (empty($var)) {
    echo '$var is either 0, empty, or not set at all';
}

// Evaluates as true because $var is set
if (isset($var)) {
    echo '$var is set even though it is empty';
}
?>
]]>
    </programlisting>
   </example>
  </para>
  <example>
   <title><function>empty</function> on String Offsets</title>
   <para>
    PHP 5.4 changes how <function>empty</function> behaves
    when passed string offsets.
   </para>
   <programlisting role="php">
<![CDATA[
<?php
$expected_array_got_string = 'somestring';
var_dump(empty($expected_array_got_string['some_key']));
var_dump(empty($expected_array_got_string[0]));
var_dump(empty($expected_array_got_string['0']));
var_dump(empty($expected_array_got_string[0.5]));
var_dump(empty($expected_array_got_string['0.5']));
var_dump(empty($expected_array_got_string['0 Mostel']));
?>
]]>
   </programlisting>
   &example.outputs.53;
   <screen>
<![CDATA[
bool(false)
bool(false)
bool(false)
bool(false)
bool(false)
bool(false)
]]>
   </screen>
   &example.outputs.54;
   <screen>
<![CDATA[
bool(true)
bool(false)
bool(false)
bool(false)
bool(true)
bool(true)
]]>
   </screen>
  </example>
 </refsect1>
 <refsect1 role="notes">
  &reftitle.notes;
  &note.language-construct;
  <note>
   <para>
    When using <function>empty</function> on inaccessible object properties,
    the <link linkend="object.isset">__isset()</link>
    overloading method will be called, if declared.
   </para>
  </note>
 </refsect1>
 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>isset</function></member>
    <member><link linkend="object.isset">__isset()</link></member>
    <member><function>unset</function></member>
    <member><function>array_key_exists</function></member>
    <member><function>count</function></member> 
    <member><function>strlen</function></member>
    <member><link linkend="types.comparisons">The type comparison tables</link></member>
   </simplelist>
  </para>
 </refsect1>
</refentry>

<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
indent-tabs-mode:nil
sgml-parent-document:nil
sgml-default-dtd-file:"~/.phpdoc/manual.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
vim600: syn=xml fen fdm=syntax fdl=2 si
vim: et tw=78 syn=sgml
vi: ts=1 sw=1
-->