Source of: /manual/en/migration5.incompatible.php
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<div id="migration5.incompatible" class="section">
<h2 class="title">Backward Incompatible Changes</h2>
<p class="para">
Although most existing PHP 4 code should work without changes, you should
pay attention to the following backward incompatible changes:
</p>
<ul class="itemizedlist">
<li class="listitem">
<span class="simpara">
There are some <a href="reserved.keywords.php" class="link">new reserved
keywords</a>.
</span>
</li>
<li class="listitem">
<span class="simpara">
<a href="function.strrpos.php" class="function">strrpos()</a> and <a href="function.strripos.php" class="function">strripos()</a> now use
the entire string as a needle.
</span>
</li>
<li class="listitem">
<span class="simpara">
Illegal use of string offsets causes <b><tt class="constant">E_ERROR</tt></b> instead
of <b><tt class="constant">E_WARNING</tt></b>. An example illegal use is:
<i>$str = 'abc'; unset($str[0]);</i>.
</span>
</li>
<li class="listitem">
<span class="simpara">
<a href="function.array-merge.php" class="function">array_merge()</a> was changed to accept only arrays. If a
non-array variable is passed, a <b><tt class="constant">E_WARNING</tt></b> will be
thrown for every such parameter. Be careful because your code may start
emitting <b><tt class="constant">E_WARNING</tt></b> out of the blue.
</span>
</li>
<li class="listitem">
<span class="simpara">
<b><tt class="constant">PATH_TRANSLATED</tt></b> server variable is no longer set implicitly under
Apache2 SAPI in contrast to the situation in PHP 4, where it is set to
the same value as the <b><tt class="constant">SCRIPT_FILENAME</tt></b> server variable when it is not
populated by Apache. This change was made to comply with the <a href="http://hoohoo.ncsa.uiuc.edu/cgi/" class="link external">» CGI specification</a>. Please refer to <a href="http://bugs.php.net/23610" class="link external">» bug #23610</a> for further information,
and see also the <var class="varname"><a href="reserved.variables.server.php" class="classname">$_SERVER['PATH_TRANSLATED']</a></var>
description in the manual. This issue
also affects PHP versions >= 4.3.2.
</span>
</li>
<li class="listitem">
<span class="simpara">
The <b><tt class="constant">T_ML_COMMENT</tt></b> constant is no longer defined by
the <a href="ref.tokenizer.php" class="link">Tokenizer</a> extension. If
error_reporting is set to <b><tt class="constant">E_ALL</tt></b>, PHP will
generate a notice. Although the <b><tt class="constant">T_ML_COMMENT</tt></b> was
never used at all, it was defined in PHP 4. In both PHP 4 and PHP 5
// and /* */ are resolved as the <b><tt class="constant">T_COMMENT</tt></b>
constant. However the PHPDoc style comments <i>/** */</i>, which starting PHP
5 are parsed by PHP, are recognized as <b><tt class="constant">T_DOC_COMMENT</tt></b>.
</span>
</li>
<li class="listitem">
<span class="simpara">
<var class="varname"><a href="reserved.variables.server.php" class="classname">$_SERVER</a></var> should be populated with <var class="varname">argc</var> and
<var class="varname">argv</var> if
<a href="ini.core.php#ini.variables-order" class="link">variables_order</a> includes "S".
If you have specifically configured your system to not create
<var class="varname"><a href="reserved.variables.server.php" class="classname">$_SERVER</a></var>, then of course it shouldn't be there.
The change was to always make <var class="varname">argc</var>
and <var class="varname">argv</var> available in the CLI version regardless of the
<a href="ini.core.php#ini.variables-order" class="link">variables_order</a> setting.
As in, the CLI version will now always populate the global
<var class="varname"><a href="reserved.variables.argc.php" class="classname">$argc</a></var> and <var class="varname"><a href="reserved.variables.argv.php" class="classname">$argv</a></var> variables.
</span>
</li>
<li class="listitem">
<span class="simpara">
An object with no properties is no longer considered "empty".
</span>
</li>
<li class="listitem">
<span class="simpara">
In some cases classes must be declared before use. It only happens if
some of the new features of PHP 5 (such as <a href="language.oop5.interfaces.php" class="link">interfaces</a>) are used.
Otherwise the behaviour is the old.
</span>
</li>
<li class="listitem">
<span class="simpara">
<a href="function.get-class.php" class="function">get_class()</a>, <a href="function.get-parent-class.php" class="function">get_parent_class()</a>
and <a href="function.get-class-methods.php" class="function">get_class_methods()</a> now return the name of the
classes/methods as they were declared (case-sensitive) which may lead to
problems in older scripts that rely on the previous behaviour (the
class/method name was always returned lowercased). A possible solution
is to search for those functions in all your scripts and use
<a href="function.strtolower.php" class="function">strtolower()</a>.
</span>
<span class="simpara">
This case sensitivity change also applies to the
<a href="language.constants.predefined.php" class="link">magical predefined
constants</a> <b><tt class="constant">__CLASS__</tt></b>,
<b><tt class="constant">__METHOD__</tt></b>, and <b><tt class="constant">__FUNCTION__</tt></b>.
The values are returned exactly as they're declared (case-sensitive).
</span>
</li>
<li class="listitem">
<span class="simpara">
<a href="function.ip2long.php" class="function">ip2long()</a> now returns <b><tt class="constant">FALSE</tt></b> when an invalid IP
address is passed as argument to the function, and no longer
<i>-1</i>.
</span>
</li>
<li class="listitem">
<span class="simpara">
If there are functions defined in the included file, they can be used in the
main file independent if they are before <a href="function.return.php" class="function">return()</a> or after.
If the file is included twice, PHP 5 issues fatal error because functions
were already declared, while PHP 4 doesn't complain about it.
It is recommended to use <a href="function.include-once.php" class="function">include_once()</a> instead of
checking if the file was already included and conditionally return inside
the included file.
</span>
</li>
<li class="listitem">
<span class="simpara">
<a href="function.include-once.php" class="function">include_once()</a> and <a href="function.require-once.php" class="function">require_once()</a>
first normalize the path of included file on Windows so that including
A.php and a.php include the file just once.
</span>
</li>
<li class="listitem">
<span class="simpara">
Passing an array to a function by value no longer resets the
array's internal pointer for array accesses made within the
function. In other words, in PHP 4 when you passed an array to a
function, its internal pointer inside the function would be
reset, while in PHP 5, when you pass an array to a function, its
array pointer within the function will be wherever it was when
the array was passed to the function.
</span>
</li>
</ul>
<p class="para">
</p><div class="example">
<p><b>Example #1 <a href="function.strrpos.php" class="function">strrpos()</a> and <a href="function.strripos.php" class="function">strripos()</a> now
use the entire string as a needle</b></p>
<div class="example-contents programlisting">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">strrpos</span><span style="color: #007700">(</span><span style="color: #DD0000">'ABCDEF'</span><span style="color: #007700">,</span><span style="color: #DD0000">'DEF'</span><span style="color: #007700">)); </span><span style="color: #FF8000">//int(3)<br /><br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">strrpos</span><span style="color: #007700">(</span><span style="color: #DD0000">'ABCDEF'</span><span style="color: #007700">,</span><span style="color: #DD0000">'DAF'</span><span style="color: #007700">)); </span><span style="color: #FF8000">//bool(false)<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div><p>
</p>
<p class="para">
</p><div class="example">
<p><b>Example #2 An object with no properties is no longer considered "empty"</b></p>
<div class="example-contents programlisting">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">class </span><span style="color: #0000BB">test </span><span style="color: #007700">{ }<br /></span><span style="color: #0000BB">$t </span><span style="color: #007700">= new </span><span style="color: #0000BB">test</span><span style="color: #007700">();<br /><br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(empty(</span><span style="color: #0000BB">$t</span><span style="color: #007700">)); </span><span style="color: #FF8000">// echo bool(false)<br /><br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">$t</span><span style="color: #007700">) {<br /> </span><span style="color: #FF8000">// Will be executed<br /></span><span style="color: #007700">}<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div><p>
</p>
<p class="para">
</p><div class="example">
<p><b>Example #3 In some cases classes must be declared before used</b></p>
<div class="example-contents programlisting">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /><br /></span><span style="color: #FF8000">//works with no errors:<br /></span><span style="color: #0000BB">$a </span><span style="color: #007700">= new </span><span style="color: #0000BB">a</span><span style="color: #007700">();<br />class </span><span style="color: #0000BB">a </span><span style="color: #007700">{<br />}<br /><br /><br /></span><span style="color: #FF8000">//throws an error:<br /></span><span style="color: #0000BB">$a </span><span style="color: #007700">= new </span><span style="color: #0000BB">b</span><span style="color: #007700">();<br /><br />interface </span><span style="color: #0000BB">c</span><span style="color: #007700">{<br />}<br />class </span><span style="color: #0000BB">b </span><span style="color: #007700">implements </span><span style="color: #0000BB">c </span><span style="color: #007700">{<br />} <br /><br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div><p>
</p>
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