language.types.boolean.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>Booleans</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.types.html">Types</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.types.integer.html">Integers</a></div> <div class="up"><a href="language.types.html">Types</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><div id="language.types.boolean" class="sect1"> <h2 class="title">Booleans</h2> <p class="simpara"> This is the simplest type. A <a href="language.types.boolean.html" class="type boolean">boolean</a> expresses a truth value. It can be either <b><tt>TRUE</tt></b> or <b><tt>FALSE</tt></b>. </p> <blockquote><p><b class="note">Note</b>: <span class="simpara"> The <a href="language.types.boolean.html" class="type boolean">boolean</a> type was introduced in PHP 4. </span> </p></blockquote> <div id="language.types.boolean.syntax" class="sect2"> <h3 class="title">Syntax</h3> <p class="para"> To specify a <a href="language.types.boolean.html" class="type boolean">boolean</a> literal, use the keywords <b><tt>TRUE</tt></b> or <b><tt>FALSE</tt></b>. Both are case-insensitive. </p> <div class="informalexample"> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br />$foo </span><span style="color: #007700">= </span><span style="color: #0000BB">True</span><span style="color: #007700">; </span><span style="color: #FF8000">// assign the value TRUE to $foo<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> <p class="para"> Typically, some kind of <a href="language.operators.html" class="link">operator</a> which returns a <a href="language.types.boolean.html" class="type boolean">boolean</a> value, and the value is passed on to a <a href="language.control-structures.html" class="link">control structure</a>. </p> <div class="informalexample"> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// == is an operator which test<br />// equality and returns a boolean<br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">$action </span><span style="color: #007700">== </span><span style="color: #DD0000">"show_version"</span><span style="color: #007700">) {<br /> echo </span><span style="color: #DD0000">"The version is 1.23"</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #FF8000">// this is not necessary...<br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">$show_separators </span><span style="color: #007700">== </span><span style="color: #0000BB">TRUE</span><span style="color: #007700">) {<br /> echo </span><span style="color: #DD0000">"<hr>\n"</span><span style="color: #007700">;<br />}<br /><br /></span><span style="color: #FF8000">// ...because instead, this can be used:<br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">$show_separators</span><span style="color: #007700">) {<br /> echo </span><span style="color: #DD0000">"<hr>\n"</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </div> <div id="language.types.boolean.casting" class="sect2"> <h3 class="title">Converting to boolean</h3> <p class="simpara"> To explicitly convert a value to <a href="language.types.boolean.html" class="type boolean">boolean</a>, use the <i>(bool)</i> or <i>(boolean)</i> casts. However, in most cases the cast is unncecessary, since a value will be automatically converted if an operator, function or control structure requires a <a href="language.types.boolean.html" class="type boolean">boolean</a> argument. </p> <p class="simpara"> See also <a href="language.types.type-juggling.html" class="link">Type Juggling</a>. </p> <p class="para"> When converting to <a href="language.types.boolean.html" class="type boolean">boolean</a>, the following values are considered <b><tt>FALSE</tt></b>: </p> <ul class="itemizedlist"> <li class="listitem"> <span class="simpara"> the <a href="language.types.boolean.html" class="link">boolean</a> <b><tt>FALSE</tt></b> itself </span> </li> <li class="listitem"> <span class="simpara"> the <a href="language.types.integer.html" class="link">integer</a> 0 (zero) </span> </li> <li class="listitem"> <span class="simpara"> the <a href="language.types.float.html" class="link">float</a> 0.0 (zero) </span> </li> <li class="listitem"> <span class="simpara"> the empty <a href="language.types.string.html" class="link">string</a>, and the <a href="language.types.string.html" class="link">string</a> "0" </span> </li> <li class="listitem"> <span class="simpara"> an <a href="language.types.array.html" class="link">array</a> with zero elements </span> </li> <li class="listitem"> <span class="simpara"> an <a href="language.types.object.html" class="link">object</a> with zero member variables (PHP 4 only) </span> </li> <li class="listitem"> <span class="simpara"> the special type <a href="language.types.null.html" class="link">NULL</a> (including unset variables) </span> </li> <li class="listitem"> <span class="simpara"> <a href="ref.simplexml.html" class="link">SimpleXML</a> objects created from empty tags </span> </li> </ul> <p class="para"> Every other value is considered <b><tt>TRUE</tt></b> (including any <a href="language.types.resource.html" class="link">resource</a>). </p> <div class="warning"><b class="warning">Warning</b> <p class="simpara"> <i>-1</i> is considered <b><tt>TRUE</tt></b>, like any other non-zero (whether negative or positive) number! </p> </div> <div class="informalexample"> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br />var_dump</span><span style="color: #007700">((bool) </span><span style="color: #DD0000">""</span><span style="color: #007700">); </span><span style="color: #FF8000">// bool(false)<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">((bool) </span><span style="color: #0000BB">1</span><span style="color: #007700">); </span><span style="color: #FF8000">// bool(true)<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">((bool) -</span><span style="color: #0000BB">2</span><span style="color: #007700">); </span><span style="color: #FF8000">// bool(true)<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">((bool) </span><span style="color: #DD0000">"foo"</span><span style="color: #007700">); </span><span style="color: #FF8000">// bool(true)<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">((bool) </span><span style="color: #0000BB">2.3e5</span><span style="color: #007700">); </span><span style="color: #FF8000">// bool(true)<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">((bool) array(</span><span style="color: #0000BB">12</span><span style="color: #007700">)); </span><span style="color: #FF8000">// bool(true)<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">((bool) array()); </span><span style="color: #FF8000">// bool(false)<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">((bool) </span><span style="color: #DD0000">"false"</span><span style="color: #007700">); </span><span style="color: #FF8000">// bool(true)<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </div></div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="language.types.html">Types</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.types.integer.html">Integers</a></div> <div class="up"><a href="language.types.html">Types</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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