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

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<!-- $Revision: 1.4 $ -->
<!-- splitted from ./en/functions/var.xml, last change in rev 1.2 -->
  <refentry id="function.empty">
   <refnamediv>
    <refname>empty</refname>
    <refpurpose>Determine whether a variable is set</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <methodsynopsis>
      <type>bool</type><methodname>empty</methodname>
      <methodparam><type>mixed</type><parameter>var</parameter></methodparam>
     </methodsynopsis>
    <note>
     <para>
      <function>empty</function> is a language construct.
     </para>
    </note>
    &note.language-construct;
    <para>
     This is the opposite of
     <literal>(boolean) <parameter>var</parameter></literal>,
     except that no warning is generated when the variable is not set.
     See <link linkend="language.types.boolean.casting">converting
     to boolean</link> for more information.
    </para>

    <!-- Returns &false; if <parameter>var</parameter> is set and has a
     non-empty or non-zero value; &true; otherwise. -->

     <informalexample>
      <programlisting role="php">
<![CDATA[
$var = 0;

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

if (!isset($var)) { // evaluates false
    echo '$var is not set at all';
}
]]>
      </programlisting>
     </informalexample>

    <simpara>
     Note that this is meaningless when used on anything which isn't a
     variable; i.e. <command>empty (addslashes ($name))</command> has
     no meaning since it would be checking whether something which
     isn't a variable is a variable with a &false; value.
     <!-- will even result in parse error (at least in PHP 4) -->
    </simpara>
    <simpara>
     See also <function>isset</function> and
     <function>unset</function>.
    </simpara>
   </refsect1>
  </refentry>

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