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<title>Checks whether a given named constant exists</title>
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<h1 class="refname">defined</h1>
<p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">defined</span> — <span class="dc-title">Checks whether a given named constant exists</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.defined-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">bool</span> <span class="methodname"><strong>defined</strong></span>
( <span class="methodparam"><span class="type">string</span> <code class="parameter">$name</code></span>
)</div>
<p class="para rdfs-comment">
Checks whether the given constant exists and is defined.
</p>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
If you want to see if a variable exists, use <span class="function"><a href="function.isset.html" class="function">isset()</a></span>
as <span class="function"><strong>defined()</strong></span> only applies to <a href="language.constants.html" class="link">constants</a>. If you want to see if a
function exists, use <span class="function"><a href="function.function-exists.html" class="function">function_exists()</a></span>.
</p>
</p></blockquote>
</div>
<div class="refsect1 parameters" id="refsect1-function.defined-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<span class="term"><em><code class="parameter">name</code></em></span>
<dd>
<p class="para">
The constant name.
</p>
</dd>
</dt>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.defined-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns <strong><code>TRUE</code></strong> if the named constant given by <em><code class="parameter">name</code></em>
has been defined, <strong><code>FALSE</code></strong> otherwise.
</p>
</div>
<div class="refsect1 examples" id="refsect1-function.defined-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-3773">
<p><strong>Example #1 Checking Constants</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">/* Note the use of quotes, this is important. This example is checking<br /> * if the string 'TEST' is the name of a constant named TEST */<br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">defined</span><span style="color: #007700">(</span><span style="color: #DD0000">'TEST'</span><span style="color: #007700">)) {<br /> echo </span><span style="color: #0000BB">TEST</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
</div>
<div class="refsect1 seealso" id="refsect1-function.defined-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"> <span class="function"><a href="function.define.html" class="function" rel="rdfs-seeAlso">define()</a> - Defines a named constant</span></li>
<li class="member"> <span class="function"><a href="function.constant.html" class="function" rel="rdfs-seeAlso">constant()</a> - Returns the value of a constant</span></li>
<li class="member"> <span class="function"><a href="function.get-defined-constants.html" class="function" rel="rdfs-seeAlso">get_defined_constants()</a> - Returns an associative array with the names of all the constants and their values</span></li>
<li class="member"> <span class="function"><a href="function.function-exists.html" class="function" rel="rdfs-seeAlso">function_exists()</a> - Return TRUE if the given function has been defined</span></li>
<li class="member">The section on <a href="language.constants.html" class="link">Constants</a></li>
</ul>
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