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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>Comparing objects</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.cloning.html">Object cloning</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.oop5.reflection.html">Reflection</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.object-comparison" class="sect1"> <h2 class="title">Comparing objects</h2> <p class="para"> In PHP 5, object comparison is more complicated than in PHP 4 and more in accordance to what one will expect from an Object Oriented Language (not that PHP 5 is such a language). </p> <p class="para"> When using the comparison operator (<i>==</i>), object variables are compared in a simple manner, namely: Two object instances are equal if they have the same attributes and values, and are instances of the same class. </p> <p class="para"> On the other hand, when using the identity operator (<i>===</i>), object variables are identical if and only if they refer to the same instance of the same class. </p> <p class="para"> An example will clarify these rules. <div class="example"> <p><b>Example #1 Example of object comparison in PHP 5</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">function </span><span style="color: #0000BB">bool2str</span><span style="color: #007700">(</span><span style="color: #0000BB">$bool</span><span style="color: #007700">)<br />{<br /> if (</span><span style="color: #0000BB">$bool </span><span style="color: #007700">=== </span><span style="color: #0000BB">false</span><span style="color: #007700">) {<br /> return </span><span style="color: #DD0000">'FALSE'</span><span style="color: #007700">;<br /> } else {<br /> return </span><span style="color: #DD0000">'TRUE'</span><span style="color: #007700">;<br /> }<br />}<br /><br />function </span><span style="color: #0000BB">compareObjects</span><span style="color: #007700">(&</span><span style="color: #0000BB">$o1</span><span style="color: #007700">, &</span><span style="color: #0000BB">$o2</span><span style="color: #007700">)<br />{<br /> echo </span><span style="color: #DD0000">'o1 == o2 : ' </span><span style="color: #007700">. </span><span style="color: #0000BB">bool2str</span><span style="color: #007700">(</span><span style="color: #0000BB">$o1 </span><span style="color: #007700">== </span><span style="color: #0000BB">$o2</span><span style="color: #007700">) . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /> echo </span><span style="color: #DD0000">'o1 != o2 : ' </span><span style="color: #007700">. </span><span style="color: #0000BB">bool2str</span><span style="color: #007700">(</span><span style="color: #0000BB">$o1 </span><span style="color: #007700">!= </span><span style="color: #0000BB">$o2</span><span style="color: #007700">) . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /> echo </span><span style="color: #DD0000">'o1 === o2 : ' </span><span style="color: #007700">. </span><span style="color: #0000BB">bool2str</span><span style="color: #007700">(</span><span style="color: #0000BB">$o1 </span><span style="color: #007700">=== </span><span style="color: #0000BB">$o2</span><span style="color: #007700">) . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br /> echo </span><span style="color: #DD0000">'o1 !== o2 : ' </span><span style="color: #007700">. </span><span style="color: #0000BB">bool2str</span><span style="color: #007700">(</span><span style="color: #0000BB">$o1 </span><span style="color: #007700">!== </span><span style="color: #0000BB">$o2</span><span style="color: #007700">) . </span><span style="color: #DD0000">"\n"</span><span style="color: #007700">;<br />}<br /><br />class </span><span style="color: #0000BB">Flag<br /></span><span style="color: #007700">{<br /> public </span><span style="color: #0000BB">$flag</span><span style="color: #007700">;<br /><br /> function </span><span style="color: #0000BB">Flag</span><span style="color: #007700">(</span><span style="color: #0000BB">$flag </span><span style="color: #007700">= </span><span style="color: #0000BB">true</span><span style="color: #007700">) {<br /> </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">flag </span><span style="color: #007700">= </span><span style="color: #0000BB">$flag</span><span style="color: #007700">;<br /> }<br />}<br /><br />class </span><span style="color: #0000BB">OtherFlag<br /></span><span style="color: #007700">{<br /> public </span><span style="color: #0000BB">$flag</span><span style="color: #007700">;<br /><br /> function </span><span style="color: #0000BB">OtherFlag</span><span style="color: #007700">(</span><span style="color: #0000BB">$flag </span><span style="color: #007700">= </span><span style="color: #0000BB">true</span><span style="color: #007700">) {<br /> </span><span style="color: #0000BB">$this</span><span style="color: #007700">-></span><span style="color: #0000BB">flag </span><span style="color: #007700">= </span><span style="color: #0000BB">$flag</span><span style="color: #007700">;<br /> }<br />}<br /><br /></span><span style="color: #0000BB">$o </span><span style="color: #007700">= new </span><span style="color: #0000BB">Flag</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$p </span><span style="color: #007700">= new </span><span style="color: #0000BB">Flag</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">$q </span><span style="color: #007700">= </span><span style="color: #0000BB">$o</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$r </span><span style="color: #007700">= new </span><span style="color: #0000BB">OtherFlag</span><span style="color: #007700">();<br /><br />echo </span><span style="color: #DD0000">"Two instances of the same class\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">compareObjects</span><span style="color: #007700">(</span><span style="color: #0000BB">$o</span><span style="color: #007700">, </span><span style="color: #0000BB">$p</span><span style="color: #007700">);<br /><br />echo </span><span style="color: #DD0000">"\nTwo references to the same instance\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">compareObjects</span><span style="color: #007700">(</span><span style="color: #0000BB">$o</span><span style="color: #007700">, </span><span style="color: #0000BB">$q</span><span style="color: #007700">);<br /><br />echo </span><span style="color: #DD0000">"\nInstances of two different classes\n"</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">compareObjects</span><span style="color: #007700">(</span><span style="color: #0000BB">$o</span><span style="color: #007700">, </span><span style="color: #0000BB">$r</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> <div class="example-contents"><p>The above example will output:</p></div> <div class="example-contents"><pre><div class="cdata"><pre>Two instances of the same classo1 == o2 : TRUEo1 != o2 : FALSEo1 === o2 : FALSEo1 !== o2 : TRUETwo references to the same instanceo1 == o2 : TRUEo1 != o2 : FALSEo1 === o2 : TRUEo1 !== o2 : FALSEInstances of two different classeso1 == o2 : FALSEo1 != o2 : TRUEo1 === o2 : FALSEo1 !== o2 : TRUE</pre></div> </pre></div> </div> </p> <blockquote><p><b class="note">Note</b>: Extensions can define own rules for their objects comparison. <br /> </p></blockquote> </div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="language.oop5.cloning.html">Object cloning</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.oop5.reflection.html">Reflection</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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