archived-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>
      <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>.
       This also applies to nested structures, such as a multidimensional array or chained properties.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>
 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns &true; if <parameter>var</parameter> does not exist or has a value that is empty or equal to zero,
   aka falsey, see <link linkend="language.types.boolean.casting">conversion to boolean</link>.
   Otherwise returns &false;.
  </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>
   <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 Mostel']));
?>
]]>
   </programlisting>
   &example.outputs;
   <screen>
<![CDATA[
bool(true)
bool(false)
bool(false)
bool(true)
bool(true)
]]>
   </screen>
  </example>
  <example>
   <title><function>empty</function> on multidimensional arrays</title>
   <programlisting role="php">
<![CDATA[
<?php
$multidimensional = [
    'some' => [
        'deep' => [
            'nested' => 'value'
        ]
    ]
];

if (!empty($multidimensional['some']['some']['nested'])) {
    $someVariable = $multidimensional['some']['deep']['nested'];
}

var_dump(empty($multidimensional['some-undefined-key']));
var_dump(empty($multidimensional['some']['deep']['unknown']));
var_dump(empty($multidimensional['some']['deep']['nested']));
?>
]]>
   </programlisting>
   &example.outputs;
   <screen>
<![CDATA[
bool(true)
bool(true)
bool(false)
]]>
   </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>

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