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  <refentry id="function.array-keys">
   <refnamediv>
    <refname>array_keys</refname>
    <refpurpose>Return all the keys of an array</refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
     <methodsynopsis>
      <type>array</type><methodname>array_keys</methodname>
      <methodparam><type>array</type><parameter>input</parameter></methodparam>
      <methodparam choice="opt"><type>mixed</type><parameter>
        search_value
       </parameter></methodparam>
     </methodsynopsis>
    <para>
     <function>array_keys</function> returns the keys, numeric and
     string, from the <parameter>input</parameter> array.
    </para>
    <para>
     If the optional <parameter>search_value</parameter> is specified,
     then only the keys for that value are returned. Otherwise, all
     the keys from the <parameter>input</parameter> are returned.
    </para>
    <para>
     <example>
      <title><function>array_keys</function> example</title>
      <programlisting role="php">
<![CDATA[
$array = array (0 => 100, "color" => "red");
print_r(array_keys ($array));

$array = array ("blue", "red", "green", "blue", "blue");
print_r(array_keys ($array, "blue"));

$array = array ("color" => array("blue", "red", "green"), "size" => array("small", "medium", "large"));
print_r(array_keys ($array));
]]>
      </programlisting>
      <para>
       The printout of the program above will be:
       <screen>
<![CDATA[
Array
(
    [0] => 0
    [1] => color
)
Array
(
    [0] => 0
    [1] => 3
    [2] => 4
)
Array
(
    [0] => color
    [1] => size
)
]]>
       </screen>
      </para>
     </example>
    </para>
    <note>
     <para>
      This function was added to PHP 4, below is an implementation for
      those still using PHP 3.
      <example>
       <title>
        Implementation of <function>array_keys</function> for PHP 3
        users
       </title>
       <programlisting role="php">
<![CDATA[
function array_keys ($arr, $term="") {
    $t = array();
    while (list($k,$v) = each($arr)) {
        if ($term && $v != $term) {
            continue;
        }
        $t[] = $k;
    }
    return $t;
}
]]>
       </programlisting>
      </example>
     </para>
    </note>
    <para>
     See also <function>array_values</function>.
    </para>
   </refsect1>
  </refentry>

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