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<title>Backward Incompatible Changes</title>
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<h2 class="title">Backward Incompatible Changes</h2>
<p class="simpara">
Although most existing PHP 5 code should work without changes, please take
note of some backward incompatible changes:
</p>
<ul class="itemizedlist">
<li class="listitem">
<span class="simpara">
The newer internal parameter parsing API has been applied across all the
extensions bundled with PHP 5.3.x. This parameter parsing API causes
functions to return <strong><code>NULL</code></strong> when passed incompatible parameters. There are
some exceptions to this rule, such as the <span class="function"><a href="function.get-class.html" class="function">get_class()</a></span>
function, which will continue to return <strong><code>FALSE</code></strong> on error.
</span>
</li>
<li class="listitem">
<span class="simpara">
<span class="function"><a href="function.clearstatcache.html" class="function">clearstatcache()</a></span> no longer clears the realpath cache by
default.
</span>
</li>
<li class="listitem">
<span class="simpara">
<span class="function"><a href="function.realpath.html" class="function">realpath()</a></span> is now fully platform-independent.
Consequence of this is that invalid relative paths such as
<em>__FILE__ . "/../x"</em> do not work anymore.
</span>
</li>
<li class="listitem">
<span class="simpara">
The <span class="function"><a href="function.call-user-func.html" class="function">call_user_func()</a></span> family of functions now propagate
<em>$this</em> even if the callee is a parent class.
</span>
</li>
<li class="listitem">
<span class="simpara">
The array functions <span class="function"><a href="function.natsort.html" class="function">natsort()</a></span>,
<span class="function"><a href="function.natcasesort.html" class="function">natcasesort()</a></span>, <span class="function"><a href="function.usort.html" class="function">usort()</a></span>,
<span class="function"><a href="function.uasort.html" class="function">uasort()</a></span>, <span class="function"><a href="function.uksort.html" class="function">uksort()</a></span>,
<span class="function"><a href="function.array-flip.html" class="function">array_flip()</a></span>, and <span class="function"><a href="function.array-unique.html" class="function">array_unique()</a></span> no
longer accept objects passed as arguments. To apply these functions to an
object, cast the object to an array first.
</span>
</li>
<li class="listitem">
<span class="simpara">
The behaviour of functions with by-reference parameters called by value has
changed. Where previously the function would accept the by-value argument,
a fatal error is now emitted. Any previous code passing constants or
literals to functions expecting references, will need altering to assign
the value to a variable before calling the function.
</span>
</li>
<li class="listitem">
<span class="simpara">
The new mysqlnd library necessitates the use of MySQL 4.1's newer 41-byte
password format. Continued use of the old 16-byte passwords will cause
<span class="function"><a href="function.mysql-connect.html" class="function">mysql_connect()</a></span> and similar functions to emit the error,
<em>"mysqlnd cannot connect to MySQL 4.1+ using old
authentication."</em>
</span>
</li>
<li class="listitem">
<span class="simpara">
The new mysqlnd library does not read mysql configuration files
(my.cnf/my.ini), as the older libmysqlclient library does. If your code relies on
settings in the configuration file, you can load it explicitly with the
<span class="function"><a href="mysqli.options.html" class="function">mysqli_options()</a></span> function. Note that this means the
PDO specific constants <strong><code>PDO::MYSQL_ATTR_READ_DEFAULT_FILE</code></strong>
and <strong><code>PDO::MYSQL_ATTR_READ_DEFAULT_GROUP</code></strong> are not defined
if MySQL support in PDO is compiled with mysqlnd.
</span>
</li>
<li class="listitem">
<span class="simpara">
The trailing / has been removed from the <a href="class.splfileinfo.html" class="classname">SplFileInfo</a>
class and other related directory classes.
</span>
</li>
<li class="listitem">
<span class="simpara">
The <a href="language.oop5.magic.html#object.tostring" class="link">__toString()</a> magic
method can no longer accept arguments.
</span>
</li>
<li class="listitem">
<span class="simpara">
The magic methods
<a href="language.oop5.overloading.html#object.get" class="link">__get()</a>,
<a href="language.oop5.overloading.html#object.set" class="link">__set()</a>,
<a href="language.oop5.overloading.html#object.isset" class="link">__isset()</a>,
<a href="language.oop5.overloading.html#object.unset" class="link">__unset()</a>, and
<a href="language.oop5.overloading.html#object.call" class="link">__call()</a> must always
be public and can no longer be static. Method signatures are now enforced.
</span>
</li>
<li class="listitem">
<span class="simpara">
The <a href="language.oop5.overloading.html#object.call" class="link">__call()</a>
magic method is now invoked on access to private and protected methods.
</span>
</li>
<li class="listitem">
<span class="simpara">
<span class="function"><a href="function.func-get-arg.html" class="function">func_get_arg()</a></span>, <span class="function"><a href="function.func-get-args.html" class="function">func_get_args()</a></span> and
<span class="function"><a href="function.func-num-args.html" class="function">func_num_args()</a></span> can no longer be called from the
outermost scope of a file that has been included by calling
<span class="function"><a href="function.include.html" class="function">include</a></span> or <span class="function"><a href="function.require.html" class="function">require</a></span> from within
a function in the calling file.
</span>
</li>
<li class="listitem">
<span class="simpara">
An emulation layer for the MHASH extension to wrap around the Hash extension
have been added. However not all the algorithms are covered, notable the
s2k hashing algorithm. This means that s2k hashing is no longer available
as of PHP 5.3.0.
</span>
</li>
</ul>
<p class="simpara">
The following keywords are now reserved and may not be used in function,
class, etc. names.
</p>
<ul class="itemizedlist">
<li class="listitem">
<span class="simpara">
<a href="control-structures.goto.html" class="link">goto</a>
</span>
</li>
<li class="listitem">
<span class="simpara">
<a href="language.namespaces.html" class="link">namespace</a>
</span>
</li>
</ul>
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