<!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>Class Constants</title>
</head>
<body><div class="manualnavbar" style="text-align: center;">
<div class="prev" style="text-align: left; float: left;"><a href="language.oop5.properties.html">Properties</a></div>
<div class="next" style="text-align: right; float: right;"><a href="language.oop5.autoload.html">Autoloading Classes</a></div>
<div class="up"><a href="language.oop5.html">Classes and Objects</a></div>
<div class="home"><a href="index.html">PHP Manual</a></div>
</div><hr /><div id="language.oop5.constants" class="sect1">
<h2 class="title">Class Constants</h2>
<p class="para">
It is possible to define constant values on a per-class basis remaining the
same and unchangeable. Constants differ from normal variables in that you
don't use the <var class="varname"><var class="varname">$</var></var> symbol to declare or use them.
</p>
<p class="para">
The value must be a constant expression, not (for example) a variable, a
property, a result of a mathematical operation, or a function call.
</p>
<p class="para">
It's also possible for interfaces to have <em>constants</em>. Look at
the <a href="language.oop5.interfaces.html" class="link">interface documentation</a> for
examples.
</p>
<p class="para">
As of PHP 5.3.0, it's possible to reference the class using a variable.
The variable's value can not be a keyword (e.g. <em>self</em>,
<em>parent</em> and <em>static</em>).
</p>
<div class="example" id="example-178">
<p><strong>Example #1 Defining and using a constant</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">class </span><span style="color: #0000BB">MyClass<br /></span><span style="color: #007700">{<br /> const </span><span style="color: #0000BB">CONSTANT </span><span style="color: #007700">= </span><span style="color: #DD0000">'constant value'</span><span style="color: #007700">;<br /><br /> function </span><span style="color: #0000BB">showConstant</span><span style="color: #007700">() {<br /> echo </span><span style="color: #0000BB">self</span><span style="color: #007700">::</span><span style="color: #0000BB">CONSTANT </span><span style="color: #007700">. </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /> }<br />}<br /><br />echo </span><span style="color: #0000BB">MyClass</span><span style="color: #007700">::</span><span style="color: #0000BB">CONSTANT </span><span style="color: #007700">. </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">$classname </span><span style="color: #007700">= </span><span style="color: #DD0000">"MyClass"</span><span style="color: #007700">;<br />echo </span><span style="color: #0000BB">$classname</span><span style="color: #007700">::</span><span style="color: #0000BB">CONSTANT </span><span style="color: #007700">. </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">; </span><span style="color: #FF8000">// As of PHP 5.3.0<br /><br /></span><span style="color: #0000BB">$class </span><span style="color: #007700">= new </span><span style="color: #0000BB">MyClass</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$class</span><span style="color: #007700">-></span><span style="color: #0000BB">showConstant</span><span style="color: #007700">();<br /><br />echo </span><span style="color: #0000BB">$class</span><span style="color: #007700">::</span><span style="color: #0000BB">CONSTANT</span><span style="color: #007700">.</span><span style="color: #DD0000">"\n"</span><span style="color: #007700">; </span><span style="color: #FF8000">// As of PHP 5.3.0<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<div class="example" id="example-179">
<p><strong>Example #2 Static data example</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">class </span><span style="color: #0000BB">foo </span><span style="color: #007700">{<br /> </span><span style="color: #FF8000">// As of PHP 5.3.0<br /> </span><span style="color: #007700">const </span><span style="color: #0000BB">BAR </span><span style="color: #007700">= <<<'EOT'<br /></span><span style="color: #DD0000">bar<br /></span><span style="color: #007700">EOT;<br />}<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
<div class="example-contents"><p>
Unlike heredocs, nowdocs can be used in any static data context.
</p></div>
</div>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
Nowdoc support was added in PHP 5.3.0.
</p>
</p></blockquote>
</div><hr /><div class="manualnavbar" style="text-align: center;">
<div class="prev" style="text-align: left; float: left;"><a href="language.oop5.properties.html">Properties</a></div>
<div class="next" style="text-align: right; float: right;"><a href="language.oop5.autoload.html">Autoloading Classes</a></div>
<div class="up"><a href="language.oop5.html">Classes and Objects</a></div>
<div class="home"><a href="index.html">PHP Manual</a></div>
</div></body></html>
