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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>Determine whether a variable is empty</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="function.doubleval.html">doubleval</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.floatval.html">floatval</a></div> <div class="up"><a href="ref.var.html">Variable handling Functions</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><div id="function.empty" class="refentry"> <div class="refnamediv"> <h1 class="refname">empty</h1> <p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">empty</span> — <span class="dc-title">Determine whether a variable is empty</span></p> </div> <div class="refsect1 description"> <h3 class="title">Description</h3> <div class="methodsynopsis dc-description"> <span class="type">bool</span> <span class="methodname"><b><b>empty</b></b></span> ( <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <tt class="parameter">$var</tt></span> )</div> <p class="para rdfs-comment"> Determine whether a variable is considered to be empty. </p> </div> <div class="refsect1 parameters"> <h3 class="title">Parameters</h3> <p class="para"> <dl> <dt> <span class="term"><i><tt class="parameter">var</tt></i></span> <dd> <p class="para"> Variable to be checked </p> <blockquote><p><b class="note">Note</b>: <b>empty()</b> only checks variables as anything else will result in a parse error. In other words, the following will not work: <strong class="command">empty(trim($name))</strong>. <br /> </p></blockquote> <p class="para"> <b>empty()</b> is the opposite of <i>(boolean) var</i>, except that no warning is generated when the variable is not set. </p> </dd> </dt> </dl> </p> </div> <div class="refsect1 returnvalues"> <h3 class="title">Return Values</h3> <p class="para"> Returns <b><tt>FALSE</tt></b> if <i><tt class="parameter">var</tt></i> has a non-empty and non-zero value. </p> <p class="para"> The following things are considered to be empty: <ul class="simplelist"> <li class="member"><i>"" (an empty string)</i></li> <li class="member"><i>0 (0 as an integer)</i></li> <li class="member"><i>"0" (0 as a string)</i></li> <li class="member"><b><tt>NULL</tt></b></li> <li class="member"><b><tt>FALSE</tt></b></li> <li class="member"><i>array() (an empty array)</i></li> <li class="member"><i>var $var; (a variable declared, but without a value in a class)</i></li> </ul> </p> </div> <div class="refsect1 changelog"> <h3 class="title">ChangeLog</h3> <p class="para"> <table class="informaltable"> <colgroup> <thead valign="middle"> <tr valign="middle"> <th colspan="1">Version</th> <th colspan="1">Description</th> </tr> </thead> <tbody valign="middle" class="tbody"> <tr valign="middle"> <td colspan="1" rowspan="1" align="left">PHP 5</td> <td colspan="1" rowspan="1" align="left"> <p class="para"> As of PHP 5, objects with no properties are no longer considered empty. </p> </td> </tr> <tr valign="middle"> <td colspan="1" rowspan="1" align="left">PHP 4</td> <td colspan="1" rowspan="1" align="left"> <p class="para"> As of PHP 4, The string value "0" is considered empty. </p> </td> </tr> </tbody> </colgroup> </table> </p> </div> <div class="refsect1 examples"> <h3 class="title">Examples</h3> <p class="para"> <div class="example"> <p><b>Example #1 A simple <b>empty()</b> / <a href="function.isset.html" class="function">isset()</a> comparison. </b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br />$var </span><span style="color: #007700">= </span><span style="color: #0000BB">0</span><span style="color: #007700">;<br /><br /></span><span style="color: #FF8000">// Evaluates to true because $var is empty<br /></span><span style="color: #007700">if (empty(</span><span style="color: #0000BB">$var</span><span style="color: #007700">)) {<br /> echo </span><span style="color: #DD0000">'$var is either 0, empty, or not set at all'</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #FF8000">// Evaluates as true because $var is set<br /></span><span style="color: #007700">if (isset(</span><span style="color: #0000BB">$var</span><span style="color: #007700">)) {<br /> echo </span><span style="color: #DD0000">'$var is set even though it is empty'</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> </div> <div class="refsect1 notes"> <h3 class="title">Notes</h3> <blockquote><p><b class="note">Note</b>: <span class="simpara">Because this is a language construct and not a function, it cannot be called using <a href="functions.variable-functions.html" class="link">variable functions</a></span></p></blockquote> </div> <div class="refsect1 seealso"> <h3 class="title">See Also</h3> <p class="para"> <ul class="simplelist"> <li class="member"><a href="function.isset.html" class="function" rel="rdfs-seeAlso">isset()</a></li> <li class="member"><a href="function.unset.html" class="function" rel="rdfs-seeAlso">unset()</a></li> <li class="member"><a href="function.array-key-exists.html" class="function" rel="rdfs-seeAlso">array_key_exists()</a></li> <li class="member"><a href="function.count.html" class="function" rel="rdfs-seeAlso">count()</a></li> <li class="member"><a href="function.strlen.html" class="function" rel="rdfs-seeAlso">strlen()</a></li> <li class="member"><a href="types.comparisons.html" class="link">The type comparison tables</a></li> </ul> </p> </div></div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="function.doubleval.html">doubleval</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.floatval.html">floatval</a></div> <div class="up"><a href="ref.var.html">Variable handling Functions</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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