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<div class="info"><h1 class="title">Using old code with new versions of PHP</h1></div>
<p class="para">
Now that PHP has grown to be a popular scripting language, there are
a lot of public repositories and libraries containing code you can reuse.
The PHP developers have largely tried to preserve backwards compatibility,
so a script written for an older version will run (ideally) without changes
in a newer version of PHP. In practice, some changes will usually be needed.
</p>
<p class="para">
Two of the most important recent changes that affect old code are:
<ul class="itemizedlist">
<li class="listitem">
<span class="simpara">
The old <var class="varname"><var class="varname">$HTTP_*_VARS</var></var> arrays are not available as of
PHP 5.4.0. The following
<a href="language.variables.superglobals.html" class="link">superglobal arrays</a>
were introduced in PHP <a href="http://www.php.net/releases/4_1_0.php" class="link external">» 4.1.0</a>.
They are: <var class="varname"><var class="varname"><a href="reserved.variables.get.html" class="classname">$_GET</a></var></var>, <var class="varname"><var class="varname"><a href="reserved.variables.post.html" class="classname">$_POST</a></var></var>,
<var class="varname"><var class="varname"><a href="reserved.variables.cookies.html" class="classname">$_COOKIE</a></var></var>, <var class="varname"><var class="varname"><a href="reserved.variables.server.html" class="classname">$_SERVER</a></var></var>,
<var class="varname"><var class="varname"><a href="reserved.variables.files.html" class="classname">$_FILES</a></var></var>, <var class="varname"><var class="varname"><a href="reserved.variables.environment.html" class="classname">$_ENV</a></var></var>,
<var class="varname"><var class="varname"><a href="reserved.variables.request.html" class="classname">$_REQUEST</a></var></var>, and <var class="varname"><var class="varname"><a href="reserved.variables.session.html" class="classname">$_SESSION</a></var></var>.
</span>
</li>
<li class="listitem">
<span class="simpara">
External variables are no longer registered in the global scope by
default. In other words, as of PHP
<a href="http://www.php.net/releases/4_2_0.php" class="link external">» 4.2.0</a> the PHP directive
<a href="ini.core.html#ini.register-globals" class="link">register_globals</a> is
<em class="emphasis">off</em> by default in <var class="filename">php.ini</var>. The preferred
method of accessing these values is via the superglobal arrays mentioned
above. Older scripts, books, and tutorials may rely on this
directive being <em>on</em>. If it were <em>on</em>,
for example, one could use <var class="varname"><var class="varname">$id</var></var> from the URL
<em>http://www.example.com/foo.php?id=42</em>. Whether on
or off, <var class="varname"><var class="varname"><a href="reserved.variables.get.html" class="classname">$_GET['id']</a></var></var> is available.
</span>
</li>
</ul>
For more details on these changes, see the section on
<a href="language.variables.predefined.html" class="link">predefined variables</a>
and links therein.
</p>
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