📄 function.require-once.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>require_once</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.include.html">include</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.include-once.html">include_once</a></div> <div class="up"><a href="language.control-structures.html">Control Structures</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><div id="function.require-once" class="sect1"> <h2 class="title"><b>require_once()</b></h2> <p class="para"> The <b>require_once()</b> statement includes and evaluates the specified file during the execution of the script. This is a behavior similar to the <b>require()</b> statement, with the only difference being that if the code from a file has already been included, it will not be included again. See the documentation for <b>require()</b> for more information on how this statement works. </p> <p class="para"> <b>require_once()</b> should be used in cases where the same file might be included and evaluated more than once during a particular execution of a script, and you want to be sure that it is included exactly once to avoid problems with function redefinitions, variable value reassignments, etc. </p> <p class="para"> For examples on using <b>require_once()</b> and <b>include_once()</b>, look at the <a href="http://pear.php.net/" class="link external">» PEAR</a> code included in the latest PHP source code distributions. </p> <p class="para"> Return values are the same as with <b>include()</b>. If the file was already included, this function returns <b><tt>TRUE</tt></b> </p> <p class="para"> <blockquote><p><b class="note">Note</b>: <b>require_once()</b> was added in PHP 4.0.1 <br /> </p></blockquote> </p> <p class="para"> <blockquote><p><b class="note">Note</b>: Be aware, that the behaviour of <b>require_once()</b> and <b>include_once()</b> may not be what you expect on a non case sensitive operating system (such as Windows). <div class="example"> <p><b>Example #1 <b>require_once()</b> is case insensitive on Windows</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">require_once </span><span style="color: #DD0000">"a.php"</span><span style="color: #007700">; </span><span style="color: #FF8000">// this will include a.php<br /></span><span style="color: #007700">require_once </span><span style="color: #DD0000">"A.php"</span><span style="color: #007700">; </span><span style="color: #FF8000">// this will include a.php again on Windows! (PHP 4 only)<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> This behaviour changed in PHP 5 - the path is normalized first so that <var class="filename">C:\PROGRA~1\A.php</var> is realized the same as <var class="filename">C:\Program Files\a.php</var> and the file is required just once. <br /> </p></blockquote> </p> <div class="warning"><b class="warning">Warning</b><p class="para">Windows versions of PHPprior to PHP 4.3.0 do not support access of remote files via this function,even if <a href="filesystem.configuration.html#ini.allow-url-fopen" class="link">allow_url_fopen</a> is enabled.</p></div> <p class="para"> See also <b>require()</b>, <b>include()</b>, <b>include_once()</b>, <a href="function.get-required-files.html" class="function">get_required_files()</a>, <a href="function.get-included-files.html" class="function">get_included_files()</a>, <a href="function.readfile.html" class="function">readfile()</a>, and <a href="function.virtual.html" class="function">virtual()</a>. </p> </div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="function.include.html">include</a></div> <div class="next" style="text-align: right; float: right;"><a href="function.include-once.html">include_once</a></div> <div class="up"><a href="language.control-structures.html">Control Structures</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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