php-doc-en/reference/array/functions/array-keys.xml

<?xml version="1.0" encoding="utf-8"?>
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<refentry xmlns="http://docbook.org/ns/docbook" xml:id="function.array-keys">
 <refnamediv>
  <refname>array_keys</refname>
  <refpurpose>Return all the keys or a subset of the keys of an array</refpurpose>
 </refnamediv>
 
 <refsect1 role="description">
  &reftitle.description;
  <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>
   <methodparam choice="opt"><type>bool</type><parameter>strict</parameter><initializer>false</initializer></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>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>input</parameter></term>
     <listitem>
      <para>
       An array containing keys to return.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>search_value</parameter></term>
     <listitem>
      <para>
       If specified, then only keys containing these values are returned.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>strict</parameter></term>
     <listitem>
      <para>
       Determines if strict comparison (===) should be used during the search.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   Returns an array of all the keys in <parameter>input</parameter>.
  </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>
        Added the <parameter>strict</parameter> parameter.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>
 
 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>array_keys</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
$array = array(0 => 100, "color" => "red");
print_r(array_keys($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>
    &example.outputs;
    <screen>
<![CDATA[
Array
(
    [0] => 0
    [1] => color
)
Array
(
    [0] => 0
    [1] => 3
    [2] => 4
)
Array
(
    [0] => color
    [1] => size
)
]]>
    </screen>
   </example>
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>array_values</function></member>
    <member><function>array_key_exists</function></member>
    <member><function>array_search</function></member>
   </simplelist>
  </para>
 </refsect1>
</refentry>

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