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<title>Return all the keys or a subset of the keys of an array</title>
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<div class="refnamediv">
<h1 class="refname">array_keys</h1>
<p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">array_keys</span> — <span class="dc-title">Return all the keys or a subset of the keys of an array</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.array-keys-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">array</span> <span class="methodname"><strong>array_keys</strong></span>
( <span class="methodparam"><span class="type">array</span> <code class="parameter">$array</code></span>
[, <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$search_value</code><span class="initializer"> = <strong><code>NULL</code></strong></span></span>
[, <span class="methodparam"><span class="type">bool</span> <code class="parameter">$strict</code><span class="initializer"> = false</span></span>
]] )</div>
<p class="para rdfs-comment">
<span class="function"><strong>array_keys()</strong></span> returns the keys, numeric and
string, from the <em><code class="parameter">array</code></em>.
</p>
<p class="para">
If the optional <em><code class="parameter">search_value</code></em> is specified,
then only the keys for that value are returned. Otherwise, all
the keys from the <em><code class="parameter">array</code></em> are returned.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.array-keys-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<span class="term"><em><code class="parameter">array</code></em></span>
<dd>
<p class="para">
An array containing keys to return.
</p>
</dd>
</dt>
<dt>
<span class="term"><em><code class="parameter">search_value</code></em></span>
<dd>
<p class="para">
If specified, then only keys containing these values are returned.
</p>
</dd>
</dt>
<dt>
<span class="term"><em><code class="parameter">strict</code></em></span>
<dd>
<p class="para">
Determines if strict comparison (===) should be used during the search.
</p>
</dd>
</dt>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.array-keys-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns an array of all the keys in <em><code class="parameter">array</code></em>.
</p>
</div>
<div class="refsect1 changelog" id="refsect1-function.array-keys-changelog">
<h3 class="title">Changelog</h3>
<p class="para">
<table class="doctable informaltable">
<thead>
<tr>
<th>Version</th>
<th>Description</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td>5.0.0</td>
<td>
Added the <em><code class="parameter">strict</code></em> parameter.
</td>
</tr>
</tbody>
</table>
</p>
</div>
<div class="refsect1 examples" id="refsect1-function.array-keys-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-4956">
<p><strong>Example #1 <span class="function"><strong>array_keys()</strong></span> example</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$array </span><span style="color: #007700">= array(</span><span style="color: #0000BB">0 </span><span style="color: #007700">=> </span><span style="color: #0000BB">100</span><span style="color: #007700">, </span><span style="color: #DD0000">"color" </span><span style="color: #007700">=> </span><span style="color: #DD0000">"red"</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">print_r</span><span style="color: #007700">(</span><span style="color: #0000BB">array_keys</span><span style="color: #007700">(</span><span style="color: #0000BB">$array</span><span style="color: #007700">));<br /><br /></span><span style="color: #0000BB">$array </span><span style="color: #007700">= array(</span><span style="color: #DD0000">"blue"</span><span style="color: #007700">, </span><span style="color: #DD0000">"red"</span><span style="color: #007700">, </span><span style="color: #DD0000">"green"</span><span style="color: #007700">, </span><span style="color: #DD0000">"blue"</span><span style="color: #007700">, </span><span style="color: #DD0000">"blue"</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">print_r</span><span style="color: #007700">(</span><span style="color: #0000BB">array_keys</span><span style="color: #007700">(</span><span style="color: #0000BB">$array</span><span style="color: #007700">, </span><span style="color: #DD0000">"blue"</span><span style="color: #007700">));<br /><br /></span><span style="color: #0000BB">$array </span><span style="color: #007700">= array(</span><span style="color: #DD0000">"color" </span><span style="color: #007700">=> array(</span><span style="color: #DD0000">"blue"</span><span style="color: #007700">, </span><span style="color: #DD0000">"red"</span><span style="color: #007700">, </span><span style="color: #DD0000">"green"</span><span style="color: #007700">),<br /> </span><span style="color: #DD0000">"size" </span><span style="color: #007700">=> array(</span><span style="color: #DD0000">"small"</span><span style="color: #007700">, </span><span style="color: #DD0000">"medium"</span><span style="color: #007700">, </span><span style="color: #DD0000">"large"</span><span style="color: #007700">));<br /></span><span style="color: #0000BB">print_r</span><span style="color: #007700">(</span><span style="color: #0000BB">array_keys</span><span style="color: #007700">(</span><span style="color: #0000BB">$array</span><span style="color: #007700">));<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
<div class="example-contents"><p>The above example will output:</p></div>
<div class="example-contents screen">
<div class="cdata"><pre>
Array
(
[0] => 0
[1] => color
)
Array
(
[0] => 0
[1] => 3
[2] => 4
)
Array
(
[0] => color
[1] => size
)
</pre></div>
</div>
</div>
</p>
</div>
<div class="refsect1 seealso" id="refsect1-function.array-keys-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"> <span class="function"><a href="function.array-values.html" class="function" rel="rdfs-seeAlso">array_values()</a> - Return all the values of an array</span></li>
<li class="member"> <span class="function"><a href="function.array-key-exists.html" class="function" rel="rdfs-seeAlso">array_key_exists()</a> - Checks if the given key or index exists in the array</span></li>
<li class="member"> <span class="function"><a href="function.array-search.html" class="function" rel="rdfs-seeAlso">array_search()</a> - Searches the array for a given value and returns the corresponding key if successful</span></li>
</ul>
</p>
</div>
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