function.defined.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>Checks whether a given named constant exists</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head> <body><div 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"> <h3 class="title">Description</h3> <div class="methodsynopsis dc-description"> <span class="type">bool</span> <span class="methodname"><b><b>defined</b></b></span> ( <span class="methodparam"><span class="type">string</span> <tt class="parameter">$name</tt></span> )</div> <p class="para rdfs-comment"> Checks whether the given constant exists and is defined. </p> <blockquote><p><b class="note">Note</b>: If you want to see if a variable exists, use <a href="function.isset.html" class="function">isset()</a> as <b>defined()</b> only applies to <a href="language.constants.html" class="link">constants</a>. If you want to see if a function exists, use <a href="function.function-exists.html" class="function">function_exists()</a>. <br /> </p></blockquote> </div> <div class="refsect1 parameters"> <h3 class="title">Parameters</h3> <p class="para"> <dl> <dt> <span class="term"><i><tt class="parameter">name</tt></i></span> <dd> <p class="para"> The constant name. </p> </dd> </dt> </dl> </p> </div> <div class="refsect1 returnvalues"> <h3 class="title">Return Values</h3> <p class="para"> Returns <b><tt>TRUE</tt></b> if the named constant given by <i><tt class="parameter">name</tt></i> has been defined, <b><tt>FALSE</tt></b> otherwise. </p> </div> <div class="refsect1 examples"> <h3 class="title">Examples</h3> <p class="para"> <div class="example"> <p><b>Example #1 Checking Constants</b></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 'CONSTANT' is the name of a constant named CONSTANT */<br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">defined</span><span style="color: #007700">(</span><span style="color: #DD0000">'CONSTANT'</span><span style="color: #007700">)) {<br /> echo </span><span style="color: #0000BB">CONSTANT</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> </div> <div class="refsect1 seealso"> <h3 class="title">See Also</h3> <p class="para"> <ul class="simplelist"> <li class="member"><a href="function.define.html" class="function" rel="rdfs-seeAlso">define()</a></li> <li class="member"><a href="function.constant.html" class="function" rel="rdfs-seeAlso">constant()</a></li> <li class="member"><a href="function.get-defined-constants.html" class="function" rel="rdfs-seeAlso">get_defined_constants()</a></li> <li class="member"><a href="function.function-exists.html" class="function" rel="rdfs-seeAlso">function_exists()</a></li> <li class="member">The section on <a href="language.constants.html" class="link">Constants</a></li> </ul> </p> </div></div><hr /><div 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>⌨️ 快捷键说明
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