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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>Class Constants</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="language.oop5.static.html">Static Keyword</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.oop5.abstract.html">Class Abstraction</a></div> <div class="up"><a href="language.oop5.html">Classes and Objects (PHP 5)</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">$</var> symbol to declare or use them. </p> <p class="para"> The value must be a constant expression, not (for example) a variable, a class member, result of a mathematical operation or a function call. </p> <p class="para"> Its also possible for interfaces to have <i>constants</i>. Look at the <a href="language.oop5.interfaces.html" class="link">interface documentation</a> for examples. </p> <p class="para"> As of PHP 5.3.0, it's possible to reference the class using a variable. The variable's value can not be a keyword (e.g. <i>self</i>, <i>parent</i> and <i>static</i>). </p> <div class="example"> <p><b>Example #1 Defining and using a constant</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #007700">class </span><span style="color: #0000BB">MyClass<br /></span><span style="color: #007700">{<br /> const </span><span style="color: #0000BB">constant </span><span style="color: #007700">= </span><span style="color: #DD0000">'constant value'</span><span style="color: #007700">;<br /><br /> function </span><span style="color: #0000BB">showConstant</span><span style="color: #007700">() {<br /> echo </span><span style="color: #0000BB">self</span><span style="color: #007700">::</span><span style="color: #0000BB">constant </span><span style="color: #007700">. </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /> }<br />}<br /><br />echo </span><span style="color: #0000BB">MyClass</span><span style="color: #007700">::</span><span style="color: #0000BB">constant </span><span style="color: #007700">. </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">$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"> <p><b>Example #2 Static data example</b></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">= <<<</span><span style="color: #DD0000">'EOT'<br /></span><span style="color: #0000BB">bar<br />EOT</span><span style="color: #007700">;<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><p><b class="note">Note</b>: Nowdoc support was added in PHP 5.3.0. <br /> </p></blockquote> </div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="language.oop5.static.html">Static Keyword</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.oop5.abstract.html">Class Abstraction</a></div> <div class="up"><a href="language.oop5.html">Classes and Objects (PHP 5)</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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