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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>Predefined Variables</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.variables.html">Variables</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.variables.scope.html">Variable scope</a></div> <div class="up"><a href="language.variables.html">Variables</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><div id="language.variables.predefined" class="sect1"> <h2 class="title">Predefined Variables</h2> <p class="simpara"> PHP provides a large number of predefined variables to any script which it runs. Many of these variables, however, cannot be fully documented as they are dependent upon which server is running, the version and setup of the server, and other factors. Some of these variables will not be available when PHP is run on the <a href="features.commandline.html" class="link">command line</a>. For a listing of these variables, please see the section on <a href="reserved.variables.html" class="link">Reserved Predefined Variables</a>. </p> <div class="warning"><b class="warning">Warning</b> <p class="simpara"> In PHP 4.2.0 and later, the default value for the PHP directive <a href="ini.core.html#ini.register-globals" class="link">register_globals</a> is <em class="emphasis">off</em>. This is a major change in PHP. Having register_globals <em class="emphasis">off</em> affects the set of predefined variables available in the global scope. For example, to get <var class="varname">DOCUMENT_ROOT</var> you'll use <var class="varname"><a href="reserved.variables.server.html" class="classname">$_SERVER['DOCUMENT_ROOT']</a></var> instead of <var class="varname">$DOCUMENT_ROOT</var>, or <var class="varname"><a href="reserved.variables.get.html" class="classname">$_GET['id']</a></var> from the URL <i>http://www.example.com/test.php?id=3</i> instead of <var class="varname">$id</var>, or <var class="varname"><a href="reserved.variables.environment.html" class="classname">$_ENV['HOME']</a></var> instead of <var class="varname">$HOME</var>. </p> <p class="simpara"> For related information on this change, read the configuration entry for <a href="ini.core.html#ini.register-globals" class="link">register_globals</a>, the security chapter on <a href="security.globals.html" class="link">Using Register Globals </a>, as well as the PHP <a href="http://www.php.net/releases/4_1_0.php" class="link external">» 4.1.0 </a> and <a href="http://www.php.net/releases/4_2_0.php" class="link external">» 4.2.0</a> Release Announcements. </p> <p class="simpara"> Using the available PHP Reserved Predefined Variables, like the <a href="language.variables.superglobals.html" class="link">superglobal arrays</a>, is preferred. </p> </div> <p class="simpara"> From version 4.1.0 onward, PHP provides an additional set of predefined arrays containing variables from the web server (if applicable), the environment, and user input. These new arrays are rather special in that they are automatically global--i.e., automatically available in every scope. For this reason, they are often known as "superglobals". (There is no mechanism in PHP for user-defined superglobals.) The superglobals are listed below; however, for a listing of their contents and further discussion on PHP predefined variables and their natures, please see the section <a href="reserved.variables.html" class="link">Reserved Predefined Variables</a>. Also, you'll notice how the older predefined variables (<var class="varname">$HTTP_*_VARS</var>) still exist. As of PHP 5.0.0, the long PHP <a href="language.variables.predefined.html" class="link">predefined variable</a>arrays may be disabled with the <a href="ini.core.html#ini.register-long-arrays" class="link">register_long_arrays</a>directive. </p> <blockquote><p><b class="note">Note</b>: <b>Variable variables</b><br /> Superglobals cannot be used as <a href="language.variables.variable.html" class="link">variable variables</a> inside functions or class methods. <br /> </p></blockquote> <blockquote><p><b class="note">Note</b>: Even though both the superglobal and HTTP_*_VARS can exist at the same time; they are not identical, so modifying one will not change the other. <br /> </p></blockquote> <p class="para"> If certain variables in <a href="ini.core.html#ini.variables-order" class="link">variables_order</a> are not set, their appropriate PHP predefined arrays are also left empty. </p> </div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="language.variables.html">Variables</a></div> <div class="next" style="text-align: right; float: right;"><a href="language.variables.scope.html">Variable scope</a></div> <div class="up"><a href="language.variables.html">Variables</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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