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<title>Checks if the given key or index exists in the array</title>
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<h1 class="refname">array_key_exists</h1>
<p class="verinfo">(PHP 4 >= 4.0.7, PHP 5)</p><p class="refpurpose"><span class="refname">array_key_exists</span> — <span class="dc-title">Checks if the given key or index exists in the array</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.array-key-exists-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">bool</span> <span class="methodname"><strong>array_key_exists</strong></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">$key</code></span>
, <span class="methodparam"><span class="type">array</span> <code class="parameter">$array</code></span>
)</div>
<p class="para rdfs-comment">
<span class="function"><strong>array_key_exists()</strong></span> returns <strong><code>TRUE</code></strong> if the
given <em><code class="parameter">key</code></em> is set in the array.
<em><code class="parameter">key</code></em> can be any value possible
for an array index.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.array-key-exists-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<span class="term"><em><code class="parameter">key</code></em></span>
<dd>
<p class="para">
Value to check.
</p>
</dd>
</dt>
<dt>
<span class="term"><em><code class="parameter">array</code></em></span>
<dd>
<p class="para">
An array with keys to check.
</p>
</dd>
</dt>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.array-key-exists-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns <strong><code>TRUE</code></strong> on success or <strong><code>FALSE</code></strong> on failure.
</p>
</div>
<div class="refsect1 examples" id="refsect1-function.array-key-exists-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-4954">
<p><strong>Example #1 <span class="function"><strong>array_key_exists()</strong></span> example</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$search_array </span><span style="color: #007700">= array(</span><span style="color: #DD0000">'first' </span><span style="color: #007700">=> </span><span style="color: #0000BB">1</span><span style="color: #007700">, </span><span style="color: #DD0000">'second' </span><span style="color: #007700">=> </span><span style="color: #0000BB">4</span><span style="color: #007700">);<br />if (</span><span style="color: #0000BB">array_key_exists</span><span style="color: #007700">(</span><span style="color: #DD0000">'first'</span><span style="color: #007700">, </span><span style="color: #0000BB">$search_array</span><span style="color: #007700">)) {<br /> echo </span><span style="color: #DD0000">"The 'first' element is in the array"</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<div class="example" id="example-4955">
<p><strong>Example #2 <span class="function"><strong>array_key_exists()</strong></span> vs <span class="function"><a href="function.isset.html" class="function">isset()</a></span></strong></p>
<div class="example-contents"><p>
<span class="function"><a href="function.isset.html" class="function">isset()</a></span> does not return <strong><code>TRUE</code></strong> for array keys
that correspond to a <strong><code>NULL</code></strong> value, while
<span class="function"><strong>array_key_exists()</strong></span> does.
</p></div>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$search_array </span><span style="color: #007700">= array(</span><span style="color: #DD0000">'first' </span><span style="color: #007700">=> </span><span style="color: #0000BB">null</span><span style="color: #007700">, </span><span style="color: #DD0000">'second' </span><span style="color: #007700">=> </span><span style="color: #0000BB">4</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// returns false<br /></span><span style="color: #007700">isset(</span><span style="color: #0000BB">$search_array</span><span style="color: #007700">[</span><span style="color: #DD0000">'first'</span><span style="color: #007700">]);<br /><br /></span><span style="color: #FF8000">// returns true<br /></span><span style="color: #0000BB">array_key_exists</span><span style="color: #007700">(</span><span style="color: #DD0000">'first'</span><span style="color: #007700">, </span><span style="color: #0000BB">$search_array</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</div>
<div class="refsect1 notes" id="refsect1-function.array-key-exists-notes">
<h3 class="title">Notes</h3>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
For backward compatibility, the following
deprecated alias may be used:
<span class="function"><a href="function.key-exists.html" class="function">key_exists()</a></span>
</p>
</p></blockquote>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
For backward compatibility reasons, <span class="function"><strong>array_key_exists()</strong></span>
will also return <strong><code>TRUE</code></strong> if <em><code class="parameter">key</code></em> is a property
defined within an <span class="type"><a href="language.types.object.html" class="type object">object</a></span> given as
<em><code class="parameter">array</code></em>. This behaviour should not be relied upon,
and care should be taken to ensure that <em><code class="parameter">array</code></em> is
an <span class="type"><a href="language.types.array.html" class="type array">array</a></span>.
</p>
<p class="para">
To check whether a property exists in an object, use
<span class="function"><a href="function.property-exists.html" class="function">property_exists()</a></span>.
</p>
</p></blockquote>
</div>
<div class="refsect1 seealso" id="refsect1-function.array-key-exists-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"> <span class="function"><a href="function.isset.html" class="function" rel="rdfs-seeAlso">isset()</a> - Determine if a variable is set and is not NULL</span></li>
<li class="member"> <span class="function"><a href="function.array-keys.html" class="function" rel="rdfs-seeAlso">array_keys()</a> - Return all the keys or a subset of the keys of an array</span></li>
<li class="member"> <span class="function"><a href="function.in-array.html" class="function" rel="rdfs-seeAlso">in_array()</a> - Checks if a value exists in an array</span></li>
<li class="member"> <span class="function"><a href="function.property-exists.html" class="function" rel="rdfs-seeAlso">property_exists()</a> - Checks if the object or class has a property</span></li>
</ul>
</p>
</div>
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