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 <appendix xml:id="migration5" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
  <title>Migrating from PHP 4 to PHP 5.0.x</title>
  <para>
   &manual.migration.seealso;
   <link linkend="migration51">5.1.x</link>, 
   <link linkend="migration52">5.2.x</link>,
   <link linkend="migration53">5.3.x</link>,
   <link linkend="migration54">5.4.x</link> and
   <link linkend="migration55">5.5.x</link>.
  </para>

  <section xml:id="migration5.changes">
   <title>What has changed in PHP 5.0.x</title>
   <para>
    PHP 5 and the integrated Zend Engine 2 have greatly improved PHP's
    performance and capabilities, but great care has been taken to break as
    little existing code as possible. So migrating your code from PHP 4 to 5
    should be very easy. Most existing PHP 4 code should be ready to run
    without changes, but you should still know about the <link
     linkend="migration5.incompatible">few differences</link> and
    take care to test your code before switching versions in production
    environments.
   </para>
  </section>

  <section xml:id="migration5.incompatible">
   <title>Backward Incompatible Changes</title>
   <para>
    Although most existing PHP 4 code should work without changes, you should
    pay attention to the following backward incompatible changes:
   </para>
   <itemizedlist>
    <listitem>
     <simpara>
      There are some <link linkend="reserved.keywords">new reserved
      keywords</link>.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>strrpos</function> and <function>strripos</function> now use
      the entire string as a needle.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      Illegal use of string offsets causes <constant>E_ERROR</constant> instead
      of <constant>E_WARNING</constant>. An example illegal use is: 
      <literal>$str = 'abc'; unset($str[0]);</literal>.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>array_merge</function> was changed to accept only arrays. If a
      non-array variable is passed, a <constant>E_WARNING</constant> will be
      thrown for every such parameter. Be careful because your code may start
      emitting <constant>E_WARNING</constant> out of the blue.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <constant>PATH_TRANSLATED</constant> 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 <constant>SCRIPT_FILENAME</constant> server variable when it is not
      populated by Apache. This change was made to comply with the <link
      xlink:href="&url.rfc;3875">CGI/1.1 specification</link>. Please refer to <link
      xlink:href="&url.php.bugs;23610">bug #23610</link> for further information,
      and see also the <varname>$_SERVER['PATH_TRANSLATED']</varname>
      description in the manual. This issue 
      also affects PHP versions &gt;= 4.3.2.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      The <constant>T_ML_COMMENT</constant> constant is no longer defined by
      the <link linkend="ref.tokenizer">Tokenizer</link> extension. If
      error_reporting is set to <constant>E_ALL</constant>, PHP will
      generate a notice. Although the <constant>T_ML_COMMENT</constant> was
      never used at all, it was defined in PHP 4. In both PHP 4 and PHP 5
      // and /* */ are resolved as the <constant>T_COMMENT</constant>
      constant. However the PHPDoc style comments <literal>/** */</literal>, which starting PHP
      5 are parsed by PHP, are recognized as <constant>T_DOC_COMMENT</constant>. 
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <varname>$_SERVER</varname> should be populated with <varname>argc</varname> and
      <varname>argv</varname> if
      <link linkend="ini.variables-order">variables_order</link> includes "S".
      If you have specifically configured your system to not create
      <varname>$_SERVER</varname>, then of course it shouldn't be there.
      The change was to always make <varname>argc</varname>
      and <varname>argv</varname> available in the CLI version regardless of the
      <link linkend="ini.variables-order">variables_order</link> setting.
      As in, the CLI version will now always populate the global
      <varname>$argc</varname> and <varname>$argv</varname> variables.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      An object with no properties is no longer considered "empty".
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      In some cases classes must be declared before use. It only happens if
      some of the new features of PHP 5 (such as <link
      linkend="language.oop5.interfaces">interfaces</link>) are used.
      Otherwise the behaviour is the old.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>get_class</function>, <function>get_parent_class</function>
      and <function>get_class_methods</function> 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
      <function>strtolower</function>.
     </simpara>
     <simpara>
      This case sensitivity change also applies to the 
      <link linkend="language.constants.predefined">magical predefined 
      constants</link> <constant>__CLASS__</constant>, 
      <constant>__METHOD__</constant>, and <constant>__FUNCTION__</constant>.
      The values are returned exactly as they're declared (case-sensitive).
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ip2long</function> now returns &false; when an invalid IP
      address is passed as argument to the function, and no longer
      <literal>-1</literal>.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      If there are functions defined in the included file, they can be used in the
      main file independent if they are before <function>return</function> 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 <function>include_once</function> instead of
      checking if the file was already included and conditionally return inside
      the included file.
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>include_once</function> and <function>require_once</function>
      first normalize the path of included file on Windows so that including
      A.php and a.php include the file just once.
     </simpara>
    </listitem>
    <listitem>
     <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.
     </simpara>
    </listitem>
   </itemizedlist>

   <para>
    <example>
     <title><function>strrpos</function> and <function>strripos</function> now
      use the entire string as a needle</title>
     <programlisting role="php">
<![CDATA[
<?php
var_dump(strrpos('ABCDEF','DEF')); //int(3)

var_dump(strrpos('ABCDEF','DAF')); //bool(false)
?>
]]>
     </programlisting>
    </example>
   </para>
   <para>
    <example>
     <title>An object with no properties is no longer considered "empty"</title>
     <programlisting role="php">
<![CDATA[
<?php
class test { }
$t = new test();

var_dump(empty($t)); // echo bool(false)

if ($t) {
    // Will be executed
}
?>
]]>
     </programlisting>
    </example>
   </para>
   <para>
    <example>
     <title>In some cases classes must be declared before used</title>
     <programlisting role="php">
<![CDATA[
<?php

//works with no errors:
$a = new a();
class a {
}


//throws an error:
$a = new b();

interface c{
}
class b implements c {
} 

?>
]]>
     </programlisting>
    </example>
   </para>
  </section>

  <section xml:id="migration5.cli-cgi">
   <title>CLI and CGI</title>
   <para>
    In PHP 5 there were some changes in CLI and CGI filenames. In PHP 5, the
    CGI version was renamed to <filename>php-cgi.exe</filename> (previously
    <filename>php.exe</filename>) and the CLI version now sits in the main
    directory (previously <filename>cli/php.exe</filename>).
   </para>
   <para>
    In PHP 5 it was also introduced a new mode:
    <filename>php-win.exe</filename>. This is equal to the CLI version, except
    that php-win doesn't output anything and thus provides no console (no "dos
    box" appears on the screen). This behavior is similar to php-gtk.
   </para>
   <para>
    In PHP 5, the CLI version will always populate the global 
    <varname>$argv</varname> and <varname>$argc</varname> variables regardless
    of any &php.ini; directive setting.  Even having  
    <link linkend="ini.register-argc-argv">register_argc_argv</link> set to
    <literal>off</literal> will have no affect in CLI.
   </para>
   <para>
    See also the <link linkend="features.commandline">command line 
    reference</link>.
   </para>
  </section>

  <section xml:id="migration5.configuration">
   <title>Migrating Configuration Files</title>
   <para>
    Since the ISAPI modules changed their names, from php4xxx to php5xxx, you
    need to make some changes in the configuration files. There were also
    changes in the CLI and CGI filenames. Please refer to the <link
     linkend="migration5.cli-cgi">corresponding section</link> for more
    information.
   </para>
   <para>
    Migrating the Apache configuration is extremely easy. See the example below
    to check the change you need to do:
    <example>
     <title>Migrating Apache configuration files for PHP 5</title>
     <programlisting role="apache-conf">
<![CDATA[
# change this line:    
LoadModule php4_module /php/sapi/php4apache2.dll

# with this one:
LoadModule php5_module /php/php5apache2.dll
]]>
     </programlisting>
    </example>
   </para>
   <para>
    If your web server is running PHP in CGI mode, you should note that the
    CGI version has changed its name from <filename>php.exe</filename> to
    <filename>php-cgi.exe</filename>.
    In Apache, you should do something like this:
    <example>
     <title>Migrating Apache configuration files for PHP 5, CGI mode</title>
     <programlisting role="apache-conf">
<![CDATA[
# change this line:    
Action application/x-httpd-php "/php/php.exe" 

# with this one:
Action application/x-httpd-php "/php/php-cgi.exe" 
]]>
     </programlisting>
    </example>
   </para>
   <para>
    In other web servers you need to change either the CGI or the ISAPI module
    filenames.
   </para>
  </section>

  <section xml:id="migration5.functions">
   <title>New Functions</title>
   <para>
    In PHP 5 there are some new functions. Here is the list of them:
   </para>
   <para><link linkend="ref.array">Arrays</link>:</para>
    <itemizedlist>
    <listitem>
     <simpara>
      <function>array_combine</function> - Creates an array by using one array
      for keys and another for its values
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>array_diff_uassoc</function> - Computes the difference of
      arrays with additional index check which is performed by a user supplied
      callback function
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>array_udiff</function> - Computes the difference of arrays by
      using a callback function for data comparison
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>array_udiff_assoc</function> - Computes the difference of
      arrays with additional index check. The data is compared by using a
      callback function
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>array_udiff_uassoc</function> - Computes the difference of
      arrays with additional index check. The data is compared by using a
      callback function. The index check is done by a callback function also
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>array_walk_recursive</function> - Apply a user function
      recursively to every member of an array
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>array_uintersect_assoc</function> - Computes the intersection of
      arrays with additional index check. The data is compared by using a
      callback function
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>array_uintersect_uassoc</function> - Computes the intersection of
      arrays with additional index check. Both the data and the indexes are compared
      by using separate callback functions
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>array_uintersect</function> - Computes the intersection of arrays.
      The data is compared by using a callback function
     </simpara>
    </listitem>
   </itemizedlist>

   <para><link linkend="ref.ibase">InterBase</link>:</para>
   <itemizedlist>
    <listitem>
     <simpara>
      <function>ibase_affected_rows</function> - Return the number of rows
      that were affected by the previous query
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_backup</function> - Initiates a backup task in the
      service manager and returns immediately
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_commit_ret</function> - Commit a transaction without
      closing it
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_db_info</function> - Request statistics about a
      database
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_drop_db</function> - Drops a database
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_errcode</function> - Return an error code
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_free_event_handler</function> - Cancels a registered
      event handler
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_gen_id</function> - Increments the named generator and
      returns its new value
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_maintain_db</function> - Execute a maintenance command
      on the database server
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_name_result</function> - Assigns a name to a result set
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_num_params</function> - Return the number of parameters
      in a prepared query
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_param_info</function> - Return information about a
      parameter in a prepared query
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_restore</function> - Initiates a restore task in the
      service manager and returns immediately
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_rollback_ret</function> - Rollback transaction and
      retain the transaction context
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_server_info</function> - Request statistics about a
      database server
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_service_attach</function> - Connect to the service manager
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_service_detach</function> - Disconnect from the
      service manager 
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_set_event_handler</function> - Register a callback
      function to be called when events are posted
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ibase_wait_event</function> - Wait for an event to be posted
      by the database
     </simpara>
    </listitem>
   </itemizedlist>

   <para><link linkend="ref.iconv">iconv</link>:</para>
   <itemizedlist>
    <listitem>
     <simpara>
      <function>iconv_mime_decode</function> - Decodes a MIME header field
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>iconv_mime_decode_headers</function> - Decodes multiple MIME
      header fields at once
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>iconv_mime_encode</function> - Composes a MIME header field
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>iconv_strlen</function> - Returns the character count of
      string
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>iconv_strpos</function> - Finds position of first occurrence
      of a needle within a haystack
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>iconv_strrpos</function> - Finds the last occurrence of a
      needle within a haystack
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>iconv_substr</function> - Cut out part of a string
     </simpara>
    </listitem>
   </itemizedlist>

   <para><link linkend="ref.stream">Streams</link>:</para>
   <itemizedlist>
    <listitem>
     <simpara>
      <function>stream_copy_to_stream</function> - Copies data from one stream
      to another
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>stream_get_line</function> - Gets line from stream resource up
      to a given delimiter
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>stream_socket_accept</function> - Accept a connection on a
      socket created by <function>stream_socket_server</function>
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>stream_socket_client</function> - Open Internet or Unix domain
      socket connection
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>stream_socket_get_name</function> - Retrieve the name of the
      local or remote sockets
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>stream_socket_recvfrom</function> - Receives data from a
      socket, connected or not
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>stream_socket_sendto</function> - Sends a message to a socket,
      whether it is connected or not
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>stream_socket_server</function> - Create an Internet or Unix
      domain server socket
     </simpara>
    </listitem>
   </itemizedlist>

   <para><link linkend="ref.datetime">Date and time related</link>:</para>
   <itemizedlist>
    <listitem>
     <simpara>
      <function>idate</function> - Format a local time/date as integer
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>date_sunset</function> - Time of sunset for a given day and
      location
    </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>date_sunrise</function> - Time of sunrise for a given day and
      location
    </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>time_nanosleep</function> - Delay for a number of seconds and
      nanoseconds
    </simpara>
    </listitem>
   </itemizedlist>

   <para><link linkend="ref.strings">Strings</link>:</para>
   <itemizedlist>
    <listitem>
     <simpara>
      <function>str_split</function> - Convert a string to an array
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>strpbrk</function> - Search a string for any of a set of
      characters
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>substr_compare</function> - Binary safe optionally case
      insensitive comparison of two strings from an offset, up to length
      characters
     </simpara>
    </listitem>
   </itemizedlist>

   <para>Other:</para>
   <itemizedlist>
    <listitem>
     <simpara>
      <function>convert_uudecode</function> - decode a uuencoded string
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>convert_uuencode</function> - uuencode a string
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>curl_copy_handle</function> - Copy a cURL handle
      along with all of its preferences
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>dba_key_split</function> - Splits a key in string
      representation into array representation
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>dbase_get_header_info</function> - Get the header info of a
      dBase database
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>dbx_fetch_row</function> - Fetches rows from a query-result
      that had the <constant>DBX_RESULT_UNBUFFERED</constant> flag set
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>fbsql_set_password</function> - Change the password for a
      given user 
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>file_put_contents</function> - Write a string to a file
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ftp_alloc</function> - Allocates space for a file to be
      uploaded
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>get_declared_interfaces</function> - Returns an array of all
      declared interfaces
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>get_headers</function> - Fetches all the headers sent by the
      server in response to a HTTP request
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>headers_list</function> - Returns a list of response headers
      sent (or ready to send)
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>http_build_query</function> - Generate URL-encoded query string
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>image_type_to_extension</function> - Get file extension for
      image-type returned by <function>getimagesize</function>,
      <function>exif_read_data</function>,
      <function>exif_thumbnail</function>,
      <function>exif_imagetype</function>
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>imagefilter</function> - Applies a filter to an image using
      custom arguments
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>imap_getacl</function> - Gets the ACL for a given mailbox
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>ldap_sasl_bind</function> - Bind to LDAP directory using SASL
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>mb_list_encodings</function> - Returns an array of all
      supported encodings
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>pcntl_getpriority</function> - Get the priority of any
      process
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>pcntl_wait</function> - Waits on or returns the status of a
      forked child as defined by the <literal>waitpid()</literal> system call
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>pg_version</function> - Returns an array with client, protocol
      and server version (when available)
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>php_check_syntax</function> - Check the syntax of the
      specified file
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>php_strip_whitespace</function> - Return source with stripped
      comments and whitespace
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>proc_nice</function> - Change the priority of the current
      process
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>pspell_config_data_dir</function> - Change location of
      language data files
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>pspell_config_dict_dir</function> - Change location of the
      main word list
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>setrawcookie</function> - Send a cookie without URL-encoding
      the value
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>scandir</function> - List files and directories inside the
      specified path
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>snmp_read_mib</function> - Reads and parses a MIB file into
      the active MIB tree
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <function>sqlite_fetch_column_types</function> - Return an array of
      column types from a particular table
     </simpara>
    </listitem>
   </itemizedlist>
   <note>
    <para>
     The <link linkend="ref.tidy">Tidy</link> extension has also changed its
     API completely.
    </para>
   </note>
  </section>


  <section xml:id="migration5.newconf">
   <title>New Directives</title>
   <para>
    There were some new &php.ini; directives introduced in PHP 5. Here is a
    list of them:
   </para>
   <itemizedlist>
    <listitem>
     <simpara>
      mail.force_extra_parameters - Force the addition of the specified
      parameters to be passed as extra parameters to the sendmail binary.
      These parameters will always replace the value of the 5th parameter to
      <function>mail</function>, even in safe mode
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <link linkend="ini.register-long-arrays">register_long_arrays</link> -
      allow/disallow PHP to register the deprecated long <varname>$HTTP_*_VARS</varname>
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <link linkend="ini.session.hash-function">session.hash_function</link> -
      select a hash function (MD5 or SHA-1)
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <link
      linkend="ini.session.hash-bits-per-character">session.hash_bits_per_character</link>
      - define how many bits are stored in each character when converting the
      binary hash data to something readable (from 4 to 6)
     </simpara>
    </listitem>
    <listitem>
     <simpara>
      <link linkend="ini.zend.ze1-compatibility-mode">zend.ze1_compatibility_mode</link> 
      - Enable compatibility mode with Zend Engine 1 (PHP 4) 
     </simpara>
    </listitem>
   </itemizedlist>
  </section>

  <section xml:id="migration5.databases">
   <title>Databases</title>
   <para>
    There were some changes in PHP 5 regarding databases (MySQL and SQLite).
   </para>
   <para>
    In PHP 5 the MySQL client libraries are not bundled, because of license
    problems and some others. For more information, read the <link
     linkend="faq.databases.mysql.php5">FAQ entry</link>.
   </para>
   <para>
    There is also a new extension, <link linkend="ref.mysqli">MySQLi (Improved
     MySQL)</link>, which is designed to work with MySQL 4.1 and above.
   </para>
   <para>
    Since PHP 5, the <link linkend="ref.sqlite">SQLite</link> extension is
    built-in PHP. SQLite is an embeddable SQL database engine and is not a
    client library used to connect to a big database server (like MySQL or
    PostgreSQL). The SQLite library reads and writes directly to and from the
    database files on disk.
   </para>
  </section>


  <section xml:id="migration5.oop">
   <title>New Object Model</title>
   <para>
    In PHP 5 there is a new Object Model. PHP's handling of objects has been
    completely rewritten, allowing for better performance and more features.
    In previous versions of PHP, objects were handled like primitive types
    (for instance integers and strings). The drawback of this method was that
    semantically the whole object was copied when a variable was assigned, or
    passed as a parameter to a method. In the new approach, objects are
    referenced by handle, and not by value (one can think of a handle as an
    object's identifier).
   </para>
   <para>
    Many PHP programmers aren't even aware of the copying quirks of the old
    object model and, therefore, the majority of PHP applications will work
    out of the box, or with very few modifications.
   </para>
   <para>
    The new Object Model is documented at the <link
     linkend="language.oop5">Language Reference</link>.
   </para>
   <para>
    In PHP 5, function with the name of a class is called as a constructor
    only if defined in the same class. In PHP 4, it is called also if defined
    in the parent class.
   </para>
   <para>
    See also the <link linkend="ini.zend.ze1-compatibility-mode">
    zend.ze1_compatibility_mode</link> directive for compatability with 
    PHP 4. 
   </para>
  </section>

  <section xml:id="migrating5.errorrep">
   <title>Error Reporting</title>
   <para>
    As of PHP 5 the error reporting
    constant <constant>E_STRICT</constant> is available, with the
    value <literal>2048</literal>. When enabled, messages will be
    issued to warn you about code usage which is deprecated or which
    may not be future-proof.
   </para>
   <note>
    <simpara>
     <constant>E_ALL</constant> does not include <constant>E_STRICT</constant>,
     so it's not enabled by default. You must explicitly set the error
     reporting level to include <constant>E_STRICT</constant> in order
     to see these messages.
    </simpara>
   </note>
   <para>
    See <link linkend="errorfunc.constants">Predefined Constants</link> for more information.
   </para>
  </section>

 </appendix>


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