<!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>Logical Operators</title> </head> <body><div class="manualnavbar" 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 class="doctable table"> <caption><strong>Logical Operators</strong></caption> <thead> <tr> <th>Example</th> <th>Name</th> <th>Result</th> </tr> </thead> <tbody class="tbody"> <tr> <td>$a and $b</td> <td>And</td> <td><strong><code>TRUE</code></strong> if both <var class="varname"><var class="varname">$a</var></var> and <var class="varname"><var class="varname">$b</var></var> are <strong><code>TRUE</code></strong>.</td> </tr> <tr> <td>$a or $b</td> <td>Or</td> <td><strong><code>TRUE</code></strong> if either <var class="varname"><var class="varname">$a</var></var> or <var class="varname"><var class="varname">$b</var></var> is <strong><code>TRUE</code></strong>.</td> </tr> <tr> <td>$a xor $b</td> <td>Xor</td> <td><strong><code>TRUE</code></strong> if either <var class="varname"><var class="varname">$a</var></var> or <var class="varname"><var class="varname">$b</var></var> is <strong><code>TRUE</code></strong>, but not both.</td> </tr> <tr> <td>! $a</td> <td>Not</td> <td><strong><code>TRUE</code></strong> if <var class="varname"><var class="varname">$a</var></var> is not <strong><code>TRUE</code></strong>.</td> </tr> <tr> <td>$a && $b</td> <td>And</td> <td><strong><code>TRUE</code></strong> if both <var class="varname"><var class="varname">$a</var></var> and <var class="varname"><var class="varname">$b</var></var> are <strong><code>TRUE</code></strong>.</td> </tr> <tr> <td>$a || $b</td> <td>Or</td> <td><strong><code>TRUE</code></strong> if either <var class="varname"><var class="varname">$a</var></var> or <var class="varname"><var class="varname">$b</var></var> is <strong><code>TRUE</code></strong>.</td> </tr> </tbody> </table> <p class="simpara"> The reason for the two different variations of "and" and "or" operators is that they operate at different precedences. (See <a href="language.operators.precedence.html" class="link">Operator Precedence</a>.) </p> <div class="example" id="example-126"> <p><strong>Example #1 Logical operators illustrated</strong></p> <div class="example-contents"> <div class="phpcode"><code><span style="color: #000000"> <span style="color: #0000BB"><?php<br /><br /></span><span style="color: #FF8000">// --------------------<br />// foo() will never get called as those operators are short-circuit<br /><br /></span><span style="color: #0000BB">$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">// --------------------<br />// "||" has a greater precedence than "or"<br /><br />// The result of the expression (false || true) is assigned to $e<br />// Acts like: ($e = (false || true))<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">;<br /><br /></span><span style="color: #FF8000">// The constant false is assigned to $f and then true is ignored<br />// Acts like: (($f = false) or true)<br /></span><span style="color: #0000BB">$f </span><span style="color: #007700">= </span><span style="color: #0000BB">false </span><span style="color: #007700">or </span><span style="color: #0000BB">true</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">$e</span><span style="color: #007700">, </span><span style="color: #0000BB">$f</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// --------------------<br />// "&&" has a greater precedence than "and"<br /><br />// The result of the expression (true && false) is assigned to $g<br />// Acts like: ($g = (true && false))<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">;<br /><br /></span><span style="color: #FF8000">// The constant true is assigned to $h and then false is ignored<br />// Acts like: (($h = true) and false)<br /></span><span style="color: #0000BB">$h </span><span style="color: #007700">= </span><span style="color: #0000BB">true </span><span style="color: #007700">and </span><span style="color: #0000BB">false</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">$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 screen"> <div class="cdata"><pre> bool(true) bool(false) bool(false) bool(true) </pre></div> </div> </div> </div><hr /><div class="manualnavbar" 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>