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

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<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.
  </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>.
       </para>
      </note>
      <para>
       <function>empty</function> is the opposite of
       <literal>(boolean) var</literal>,
       except that no warning is generated when the variable is not set.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>
 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns &false; if <parameter>var</parameter> has a non-empty
   and non-zero value.
  </para>
  <para>
   The following things are considered to be empty:
   <simplelist>
    <member><literal>"" (an empty string)</literal></member>
    <member><literal>0 (0 as an integer)</literal></member>
    <member><literal>0.0 (0 as a float)</literal></member>
    <member><literal>"0" (0 as a string)</literal></member>
    <member>&null;</member>
    <member>&false;</member>
    <member><literal>array() (an empty array)</literal></member>
    <member><literal>var $var; (a variable declared, but without a value in a class)</literal></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>5.0.0</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>
 </refsect1>
 <refsect1 role="notes">
  &reftitle.notes;
  &note.language-construct;
  <note>
   <para>
    When using <function>empty</function> on inaccessible object properties,
    the <link linkend="language.oop5.overloading.members">__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="language.oop5.overloading.members">__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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