language.operators.logical.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>Logical Operators</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.operators.increment.html">Incrementing/Decrementing Operators</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.operators.string.html">String Operators</a></div> <div class="up"><a href="language.operators.html">Operators</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><div id="language.operators.logical" class="sect1"> <h2 class="title">Logical Operators</h2> <table border="5"> <caption><b>Logical Operators</b></caption> <colgroup> <thead valign="middle"> <tr valign="middle"> <th colspan="1">Example</th> <th colspan="1">Name</th> <th colspan="1">Result</th> </tr> </thead> <tbody valign="middle" class="tbody"> <tr valign="middle"> <td colspan="1" rowspan="1" align="left">$a and $b</td> <td colspan="1" rowspan="1" align="left">And</td> <td colspan="1" rowspan="1" align="left"><b><tt>TRUE</tt></b> if both $a and $b are <b><tt>TRUE</tt></b>.</td> </tr> <tr valign="middle"> <td colspan="1" rowspan="1" align="left">$a or $b</td> <td colspan="1" rowspan="1" align="left">Or</td> <td colspan="1" rowspan="1" align="left"><b><tt>TRUE</tt></b> if either $a or $b is <b><tt>TRUE</tt></b>.</td> </tr> <tr valign="middle"> <td colspan="1" rowspan="1" align="left">$a xor $b</td> <td colspan="1" rowspan="1" align="left">Xor</td> <td colspan="1" rowspan="1" align="left"><b><tt>TRUE</tt></b> if either $a or $b is <b><tt>TRUE</tt></b>, but not both.</td> </tr> <tr valign="middle"> <td colspan="1" rowspan="1" align="left">! $a</td> <td colspan="1" rowspan="1" align="left">Not</td> <td colspan="1" rowspan="1" align="left"><b><tt>TRUE</tt></b> if $a is not <b><tt>TRUE</tt></b>.</td> </tr> <tr valign="middle"> <td colspan="1" rowspan="1" align="left">$a && $b</td> <td colspan="1" rowspan="1" align="left">And</td> <td colspan="1" rowspan="1" align="left"><b><tt>TRUE</tt></b> if both $a and $b are <b><tt>TRUE</tt></b>.</td> </tr> <tr valign="middle"> <td colspan="1" rowspan="1" align="left">$a || $b</td> <td colspan="1" rowspan="1" align="left">Or</td> <td colspan="1" rowspan="1" align="left"><b><tt>TRUE</tt></b> if either $a or $b is <b><tt>TRUE</tt></b>.</td> </tr> </tbody> </colgroup> </table> <p class="simpara"> The reason for the two different variations of "and" and "or" operators is that they operate at different precedences. (See <a href="language.operators.html#language.operators.precedence" class="link">Operator Precedence</a>.) </p> <div class="example"> <p><b>Example #1 Logical operators illustrated</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /><br /></span><span style="color: #FF8000">// foo() will never get called as those operators are short-circuit<br /></span><span style="color: #0000BB">$a </span><span style="color: #007700">= (</span><span style="color: #0000BB">false </span><span style="color: #007700">&& </span><span style="color: #0000BB">foo</span><span style="color: #007700">());<br /></span><span style="color: #0000BB">$b </span><span style="color: #007700">= (</span><span style="color: #0000BB">true </span><span style="color: #007700">|| </span><span style="color: #0000BB">foo</span><span style="color: #007700">());<br /></span><span style="color: #0000BB">$c </span><span style="color: #007700">= (</span><span style="color: #0000BB">false </span><span style="color: #007700">and </span><span style="color: #0000BB">foo</span><span style="color: #007700">());<br /></span><span style="color: #0000BB">$d </span><span style="color: #007700">= (</span><span style="color: #0000BB">true </span><span style="color: #007700">or </span><span style="color: #0000BB">foo</span><span style="color: #007700">());<br /><br /></span><span style="color: #FF8000">// "||" has a greater precedence than "or"<br /></span><span style="color: #0000BB">$e </span><span style="color: #007700">= </span><span style="color: #0000BB">false </span><span style="color: #007700">|| </span><span style="color: #0000BB">true</span><span style="color: #007700">; </span><span style="color: #FF8000">// $e will be assigned to (false || true) which is true<br /></span><span style="color: #0000BB">$f </span><span style="color: #007700">= </span><span style="color: #0000BB">false </span><span style="color: #007700">or </span><span style="color: #0000BB">true</span><span style="color: #007700">; </span><span style="color: #FF8000">// $f will be assigned to false<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">$e</span><span style="color: #007700">, </span><span style="color: #0000BB">$f</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// "&&" has a greater precedence than "and"<br /></span><span style="color: #0000BB">$g </span><span style="color: #007700">= </span><span style="color: #0000BB">true </span><span style="color: #007700">&& </span><span style="color: #0000BB">false</span><span style="color: #007700">; </span><span style="color: #FF8000">// $g will be assigned to (true && false) which is false<br /></span><span style="color: #0000BB">$h </span><span style="color: #007700">= </span><span style="color: #0000BB">true </span><span style="color: #007700">and </span><span style="color: #0000BB">false</span><span style="color: #007700">; </span><span style="color: #FF8000">// $h will be assigned to true<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">$g</span><span style="color: #007700">, </span><span style="color: #0000BB">$h</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 something similar to:</p></div> <div class="example-contents"><pre><div class="cdata"><pre>bool(true)bool(false)bool(false)bool(true)</pre></div> </pre></div> </div> </div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="language.operators.increment.html">Incrementing/Decrementing Operators</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.operators.string.html">String Operators</a></div> <div class="up"><a href="language.operators.html">Operators</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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