<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> <title>Checks whether a given named constant exists</title> </head> <body><div class="manualnavbar" style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="function.define.html">define</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.die.html">die</a></div> <div class="up"><a href="ref.misc.html">Misc. Functions</a></div> <div class="home"><a href="index.html">PHP Manual</a></div> </div><hr /><div id="function.defined" class="refentry"> <div class="refnamediv"> <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> </p> </div> </div><hr /><div class="manualnavbar" style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="function.define.html">define</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.die.html">die</a></div> <div class="up"><a href="ref.misc.html">Misc. Functions</a></div> <div class="home"><a href="index.html">PHP Manual</a></div> </div></body></html>