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git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@147957 c90b9560-bf6c-de11-be94-00142212c4b1
419 lines
12 KiB
XML
419 lines
12 KiB
XML
<?xml version="1.0" encoding="iso-8859-1"?>
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<!-- $Revision: 1.25 $ -->
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<appendix id="migration">
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<title>Migrating from PHP/FI 2 to PHP 3</title>
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<section id="migration.about">
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<title>About the incompatibilities in 3.0</title>
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<simpara>
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PHP 3.0 is rewritten from the ground up. It has a proper parser
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that is much more robust and consistent than 2.0's. 3.0 is also
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significantly faster, and uses less memory. However, some of
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these improvements have not been possible without compatibility
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changes, both in syntax and functionality.
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</simpara>
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<simpara>
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In addition, PHP's developers have tried to clean up both PHP's
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syntax and semantics in version 3.0, and this has also caused some
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incompatibilities. In the long run, we believe that these changes
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are for the better.
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</simpara>
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<simpara>
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This chapter will try to guide you through the incompatibilities
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you might run into when going from PHP/FI 2.0 to PHP 3.0 and help
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you resolve them. New features are not mentioned here unless
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necessary.
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</simpara>
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<simpara>
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A conversion program that can automatically convert your old
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PHP/FI 2.0 scripts exists. It can be found in the
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<filename class="directory">convertor</filename> subdirectory of the PHP 3.0
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distribution. This program only catches the syntax changes though,
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so you should read this chapter carefully anyway.
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</simpara>
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</section>
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<section id="migration.old-function">
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<title><literal>old_function</literal></title>
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<simpara>
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The <literal>old_function</literal> statement allows you to
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declare a function using a syntax identical to PHP/FI2 (except you
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must replace 'function' with 'old_function'.
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</simpara>
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<simpara>
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This is a deprecated feature, and should only be used by the
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PHP/FI2->PHP 3 convertor.
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</simpara>
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<warning>
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<para>
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Functions declared as <literal>old_function</literal> cannot be
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called from PHP's internal code. Among other things, this means
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you can't use them in functions such as
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<function>usort</function>, <function>array_walk</function>, and
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<function>register_shutdown_function</function>. You can get
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around this limitation by writing a wrapper function (in normal
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PHP 3 form) to call the <literal>old_function</literal>.
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</para>
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</warning>
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</section>
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<section id="migration.startendtags">
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<title>Start/end tags</title>
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<para>
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The first thing you probably will notice is that PHP's start and end
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tags have changed. The old <literal><? ></literal> form has been
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replaced by three new possible forms:
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<example>
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<title>Migration: old start/end tags</title>
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<programlisting role="php">
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<![CDATA[
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<? echo "This is PHP/FI 2.0 code.\n"; >
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]]>
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</programlisting>
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</example>
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As of version 2.0, PHP/FI also supports this variation:
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<example>
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<title>Migration: first new start/end tags</title>
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<programlisting role="php">
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<![CDATA[
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<? echo "This is PHP 3.0 code!\n"; ?>
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]]>
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</programlisting>
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</example>
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Notice that the end tag now consists of a question mark and a
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greater-than character instead of just greater-than. However, if
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you plan on using XML on your server, you will get problems with
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the first new variant, because PHP may try to execute the XML
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markup in XML documents as PHP code. Because of this, the
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following variation was introduced:
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<example>
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<title>Migration: second new start/end tags</title>
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<programlisting role="php">
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<![CDATA[
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<?php echo "This is PHP 3.0 code!\n"; ?>
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]]>
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</programlisting>
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</example>
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Some people have had problems with editors that don't understand
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the processing instruction tags at all. Microsoft FrontPage is one
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such editor, and as a workaround for these, the following variation
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was introduced as well:
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<example>
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<title>Migration: third new start/end tags</title>
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<programlisting role="php">
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<![CDATA[
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<script language="php">
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echo "This is PHP 3.0 code!\n";
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</script>
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]]>
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</programlisting>
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</example>
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</para>
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</section>
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<section id="migration.if-endif">
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<title>if..endif syntax</title>
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<para>
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The `alternative' way to write if/elseif/else statements, using if();
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elseif(); else; endif; cannot be efficiently implemented without
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adding a large amount of complexity to the 3.0 parser. Because of
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this, the syntax has been changed:
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<example>
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<title>Migration: old if..endif syntax</title>
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<programlisting role="php">
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<![CDATA[
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if ($foo);
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echo "yep\n";
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elseif ($bar);
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echo "almost\n";
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else;
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echo "nope\n";
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endif;
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]]>
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</programlisting>
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</example>
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<example>
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<title>Migration: new if..endif syntax</title>
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<programlisting role="php">
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<![CDATA[
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if ($foo):
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echo "yep\n";
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elseif ($bar):
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echo "almost\n";
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else:
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echo "nope\n";
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endif;
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]]>
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</programlisting>
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</example>
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Notice that the semicolons have been replaced by colons in all
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statements but the one terminating the expression (endif).
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</para>
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</section>
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<section id="migration.while">
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<title>while syntax</title>
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<para>
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Just like with if..endif, the syntax of while..endwhile has changed
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as well:
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<example>
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<title>Migration: old while..endwhile syntax</title>
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<programlisting role="php">
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<![CDATA[
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while ($more_to_come);
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...
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endwhile;
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]]>
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</programlisting>
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</example>
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<example>
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<title>Migration: new while..endwhile syntax</title>
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<programlisting role="php">
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<![CDATA[
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while ($more_to_come):
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...
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endwhile;
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]]>
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</programlisting>
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</example>
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</para>
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<warning>
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<simpara>
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If you use the old while..endwhile syntax in PHP 3.0,
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you will get a never-ending loop.
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</simpara>
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</warning>
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</section>
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<section id="migration.expr">
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<title>Expression types</title>
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<simpara>
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PHP/FI 2.0 used the left side of expressions to determine what type
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the result should be. PHP 3.0 takes both sides into account when
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determining result types, and this may cause 2.0 scripts to behave
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unexpectedly in 3.0.
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</simpara>
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<para>
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Consider this example:
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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$a[0]=5;
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$a[1]=7;
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$key = key($a);
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while ("" != $key) {
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echo "$keyn";
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next($a);
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}
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]]>
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</programlisting>
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</informalexample>
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In PHP/FI 2.0, this would display both of $a's indices. In PHP
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3.0, it wouldn't display anything. The reason is that in PHP 2.0,
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because the left argument's type was string, a string comparison
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was made, and indeed <literal>""</literal> does not equal
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<literal>"0"</literal>, and the loop went through. In PHP 3.0,
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when a string is compared with an integer, an integer comparison is
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made (the string is converted to an integer). This results in
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comparing <literal>atoi("")</literal> which is
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<literal>0</literal>, and <literal>variablelist</literal> which is
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also <literal>0</literal>, and since <literal>0==0</literal>, the
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loop doesn't go through even once.
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</para>
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<para>
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The fix for this is simple. Replace the while statement with:
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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while ((string)$key != "") {
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]]>
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</programlisting>
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</informalexample>
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</para>
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</section>
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<section id="migration.errors">
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<title>Error messages have changed</title>
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<simpara>
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PHP 3.0's error messages are usually more accurate than 2.0's were,
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but you no longer get to see the code fragment causing the error.
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You will be supplied with a file name and a line number for the
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error, though.
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</simpara>
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</section>
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<section id="migration.booleval">
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<title>Short-circuited boolean evaluation</title>
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<simpara>
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In PHP 3.0 boolean evaluation is short-circuited. This means that
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in an expression like <literal>(1 || test_me())</literal>, the
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function <function>test_me</function> would not be executed since
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nothing can change the result of the expression after the
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<literal>1</literal>.
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</simpara>
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<simpara>
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This is a minor compatibility issue, but may cause unexpected
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side-effects.
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</simpara>
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</section>
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<section id="migration.truefalse">
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<title>Function &true;/&false; return values</title>
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<simpara>
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Most internal functions have been rewritten so they return &true;
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when successful and &false; when failing, as opposed to 0 and -1 in
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PHP/FI 2.0, respectively. The new behaviour allows for more
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logical code, like <literal>$fp = fopen("/your/file") or
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fail("darn!");</literal>. Because PHP/FI 2.0 had no clear rules
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for what functions should return when they failed, most such
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scripts will probably have to be checked manually after using the
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2.0 to 3.0 convertor.
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</simpara>
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<para>
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<example>
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<title>Migration from 2.0: return values, old code</title>
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<programlisting role="php">
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<![CDATA[
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$fp = fopen($file, "r");
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if ($fp == -1);
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echo("Could not open $file for reading<br />\n");
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endif;
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]]>
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</programlisting>
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</example>
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<example>
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<title>Migration from 2.0: return values, new code</title>
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<programlisting role="php">
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<![CDATA[
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$fp = @fopen($file, "r") or print("Could not open $file for reading<br />\n");
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]]>
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</programlisting>
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</example>
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</para>
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</section>
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<section id="migration.other">
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<title>Other incompatibilities</title>
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<itemizedlist>
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<listitem><simpara>
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The PHP 3.0 Apache module no longer supports Apache versions
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prior to 1.2. Apache 1.2 or later is required.
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</simpara></listitem>
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<listitem><simpara>
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<function>echo</function> no longer supports a format string.
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Use the <function>printf</function> function instead.
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</simpara></listitem>
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<listitem><simpara>
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In PHP/FI 2.0, an implementation side-effect caused
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<literal>$foo[0]</literal> to have the same effect as
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<literal>$foo</literal>. This is not true for PHP 3.0.
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</simpara></listitem>
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<listitem>
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<simpara>
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Reading arrays with <literal>$array[]</literal> is no longer
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supported
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</simpara>
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<simpara>
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That is, you cannot traverse an array by having a loop that does
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<literal>$data = $array[]</literal>. Use <function>current</function>
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and <function>next</function> instead.
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</simpara>
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<simpara>
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Also, <literal>$array1[] = $array2</literal> does not
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append the values of <literal>$array2</literal> to
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<literal>$array1</literal>, but appends
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<literal>$array2</literal> as the last entry of
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<literal>$array1</literal>. See also multidimensional array
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support.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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<literal>"+"</literal> is no longer overloaded as a
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concatenation operator for strings, instead it converts it's
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arguments to numbers and performs numeric addition. Use
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<literal>"."</literal> instead.
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</simpara>
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</listitem>
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</itemizedlist>
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<example>
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<title>Migration from 2.0: concatenation for strings</title>
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<programlisting role="php">
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<![CDATA[
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echo "1" + "1";
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]]>
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</programlisting>
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<para>
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In PHP 2.0 this would echo 11, in PHP 3.0 it would
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echo 2. Instead use:
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<programlisting role="php">
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<![CDATA[
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echo "1"."1";
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]]>
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</programlisting>
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<programlisting role="php">
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<![CDATA[
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$a = 1;
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$b = 1;
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echo $a + $b;
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]]>
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</programlisting>
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</para>
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<para>
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This would echo 2 in both PHP 2.0 and 3.0.
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<programlisting role="php">
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<![CDATA[
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$a = 1;
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$b = 1;
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echo $a.$b;
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]]>
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</programlisting>
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This will echo 11 in PHP 3.0.
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</para>
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</example>
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</section>
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</appendix>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"../../manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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