php-doc-en/reference/mbstring/reference.xml

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<!-- $Revision: 1.5 $ -->
 <reference id="ref.mbstring">
  <title>Multi-Byte String Functions</title> 
  <titleabbrev>Multi-Byte String</titleabbrev>
  <partintro>

   <section id="mbstring.intro">
    &reftitle.intro;
    <para>
     There are many languages in which all characters can be expressed
     by single byte. Multi-byte character codes are used to express
     many characters for many languages. <literal>mbstring</literal>
     is developed to handle Japanese characters. However, many
     <literal>mbstring</literal> functions are able to handle
     character encoding other than Japanese.
    </para>
    <para>
     A multi-byte character encoding represents single character with
     consecutive bytes. Some character encoding has shift(escape)
     sequences to start/end multi-byte character strings. Therefore, a
     multi-byte character string may be destroyed when it is divided
     and/or counted unless multi-byte character encoding safe method
     is used. This module provides multi-byte character safe string
     functions and other utility functions such as conversion
     functions.
    </para>
    <para>
     Since PHP is basically designed for ISO-8859-1, some multi-byte
     character encoding does not work well with PHP. Therefore, it is
     important to set <literal>mbstring.internal_encoding</literal> to
     a character encoding that works with PHP.
    </para>
    <para>
     PHP4 Character Encoding Requirements 
    </para>
    <para>
     <itemizedlist>
      <listitem>
       <simpara>
        Per byte encoding
       </simpara>
      </listitem>
      <listitem>
       <simpara>
        Single byte characters in range of <literal>00h-7fh</literal>
        which is compatible with <literal>ASCII</literal>
       </simpara>
      </listitem>
      <listitem>
       <simpara>
        Multi-byte characters without <literal>00h-7fh</literal>
       </simpara>
      </listitem>
     </itemizedlist>
    </para>
    <para>
     These are examples of internal character encoding that works with
     PHP and does NOT work with PHP.
     <informalexample>
      <programlisting>
<![CDATA[
Character encodings work with PHP: 
ISO-8859-*, EUC-JP, UTF-8

Character encodings do NOT work with PHP:
JIS, SJIS
]]>
      </programlisting>
     </informalexample>
    </para>
    <para>
     Character encoding, that does not work with PHP, may be converted
     with <literal>mbstring</literal>'s HTTP input/output conversion
     feature/function.
    </para>
    <note>
     <para>
      SJIS should not be used for internal encoding unless the reader
      is familiar with parser/compiler, character encoding and
      character encoding issues.
     </para>
    </note>
    <note>
     <para>
      If you use databases with PHP, it is recommended that you use the
      same character encoding for both database and <literal>internal
      encoding</literal> for ease of use and better performance.
      </para>
     <para>
      If you are using PostgreSQL, it supports character
      encoding that is different from backend character encoding. See
      the PostgreSQL manual for details.
     </para>
    </note>
   </section>

   <section id="mbstring.installation">
     &reftitle.install;
     <para>
      <literal>mbstring</literal> is an extended module. You must
      enable the module with the <literal>configure</literal> script.
      Refer to the <link linkend="installation">Install</link> section for
      details.
     </para>
     <simpara>
      The following configure options are related to the
      <literal>mbstring</literal> module.
     </simpara>
     <para>
      <itemizedlist>
       <listitem>
        <para>
         <option role="configure">--enable-mbstring</option> : Enable
         <literal>mbstring</literal> functions. This option is
         required to use <literal>mbstring</literal> functions.
        </para>
       </listitem>
       <listitem>
        <para>
         <option role="configure">--enable-mbstr-enc-trans</option> :
         Enable HTTP input character encoding conversion using
         <literal>mbstring</literal> conversion engine. If this
         feature is enabled, HTTP input character encoding may be
         converted to <literal>mbstring.internal_encoding</literal>
         automatically.
        </para>
       </listitem>
       <listitem>
        <para>
         <option role="configure">--enable-mbregex</option> : Enable
         regular expression functions with multibyte character support.
        </para>
       </listitem>
      </itemizedlist>
     </para>
   </section>

   &reference.mbstring.ini;

   <section id="mbstring.resources">
    &reftitle.resources;
    &no.resource;
   </section>

   &reference.mbstring.constants;

   <section id="mbstring.http">
     <title>HTTP Input and Output</title>
     <para>
      HTTP input/output character encoding conversion may convert
      binary data also. Users are supposed to control character
      encoding conversion if binary data is used for HTTP
      input/output.
     </para>
     <para>
      If <literal>enctype</literal> for HTML form is set to
      <literal>multipart/form-data</literal>,
      <literal>mbstring</literal> does not convert character encoding
      in POST data. If it is the case, strings are needed to be
      converted to internal character encoding.
     </para>
     <para>
      <itemizedlist>
       <listitem>
        <simpara>
         HTTP Input
        </simpara>
        <para> There is no way to control HTTP input character
         conversion from PHP script. To disable HTTP input character
         conversion, it has to be done in &php.ini;.
         <example>
          <title>
           Disable HTTP input conversion in &php.ini;
          </title>
          <programlisting role="php">
<![CDATA[
;; Disable HTTP Input conversion
mbstring.http_input = pass
]]>
          </programlisting>
         </example>
        </para>
        <para>
         When using PHP as an Apache module, it is possible to
         override PHP ini setting per Virtual Host in
         <literal>httpd.conf</literal> or per directory with
         <literal>.htaccess</literal>. Refer to the <link
          linkend="configuration">Configuration</link> section and
         Apache Manual for details.
        </para>
       </listitem>
       <listitem>
        <simpara>
         HTTP Output
        </simpara>
        <para>
         There are several ways to enable output character encoding
         conversion. One is using &php.ini;, another
         is using <function>ob_start</function> with
         <function>mb_output_handler</function> as
         <literal>ob_start</literal> callback function.
        </para>
        <note>
         <para>
          For PHP3-i18n users, <literal>mbstring</literal>'s output
          conversion differs from PHP3-i18n. Character encoding is
          converted using output buffer.
         </para>
        </note>
       </listitem>
      </itemizedlist>
     </para>
     <para>
      <example>
       <title>&php.ini; setting example</title>
       <programlisting>
<![CDATA[
;; Enable output character encoding conversion for all PHP pages

;; Enable Output Buffering
output_buffering    = On

;; Set mb_output_handler to enable output conversion
output_handler      = mb_output_handler
]]>
       </programlisting>
      </example>
     </para>
     <para>
      <example>
       <title>Script example</title>
       <programlisting role="php">
<![CDATA[
<?php

// Enable output character encoding conversion only for this page

// Set HTTP output character encoding to SJIS
mb_http_output('SJIS');

// Start buffering and specify "mb_output_handler" as
// callback function
ob_start('mb_output_handler');

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

   <section id="mbstring.encodings">
     <title>Supported Character Encodings</title>
     <simpara>
      Currently, the following character encoding is supported by the
      <literal>mbstring</literal> module. Character encoding may
      be specified for <literal>mbstring</literal> functions'
      <literal>encoding</literal> parameter.
     </simpara>
     <para>
      The following character encoding is supported in this PHP
      extension: 
     </para>
     <para>
      <literal>UCS-4</literal>, <literal>UCS-4BE</literal>,
      <literal>UCS-4LE</literal>, <literal>UCS-2</literal>,
      <literal>UCS-2BE</literal>, <literal>UCS-2LE</literal>,
      <literal>UTF-32</literal>, <literal>UTF-32BE</literal>,
      <literal>UTF-32LE</literal>, <literal>UCS-2LE</literal>,
      <literal>UTF-16</literal>, <literal>UTF-16BE</literal>,
      <literal>UTF-16LE</literal>, <literal>UTF-8</literal>,
      <literal>UTF-7</literal>, <literal>ASCII</literal>,
      <literal>EUC-JP</literal>, <literal>SJIS</literal>,
      <literal>eucJP-win</literal>, <literal>SJIS-win</literal>,
      <literal>ISO-2022-JP</literal>, <literal>JIS</literal>,
      <literal>ISO-8859-1</literal>, <literal>ISO-8859-2</literal>,
      <literal>ISO-8859-3</literal>, <literal>ISO-8859-4</literal>,
      <literal>ISO-8859-5</literal>, <literal>ISO-8859-6</literal>,
      <literal>ISO-8859-7</literal>, <literal>ISO-8859-8</literal>,
      <literal>ISO-8859-9</literal>, <literal>ISO-8859-10</literal>,
      <literal>ISO-8859-13</literal>, <literal>ISO-8859-14</literal>,
      <literal>ISO-8859-15</literal>, <literal>byte2be</literal>,
      <literal>byte2le</literal>, <literal>byte4be</literal>,
      <literal>byte4le</literal>, <literal>BASE64</literal>,
      <literal>7bit</literal>, <literal>8bit</literal> and
      <literal>UTF7-IMAP</literal>.
     </para>
     <para>
      &php.ini; entry, which accepts encoding name,
      accepts &quot;<literal>auto</literal>&quot; and
      &quot;<literal>pass</literal>&quot; also.
      <literal>mbstring</literal> functions, which accepts encoding
      name, and accepts &quot;<literal>auto</literal>&quot;.
     </para>
     <para>
      If &quot;<literal>pass</literal>&quot; is set, no character
      encoding conversion is performed.
     </para>
     <para>
      If &quot;<literal>auto</literal>&quot; is set, it is expanded to
      &quot;<literal>ASCII,JIS,UTF-8,EUC-JP,SJIS</literal>&quot;.
     </para>
     <para>
      See also <function>mb_detect_order</function>
     </para>
     <note>
      <para>
       &quot;Supported character encoding&quot; does not mean that it
       works as internal character code.
      </para>
     </note>
   </section>
    
   <section id="mbstring.overload">
     <title>
      Overloading PHP string functions with multi byte string functions
     </title>
     <para>
      Because almost PHP application written for language using
      single-byte character encoding, there are some difficulties for
      multibyte string handling including japanese. Almost PHP string
      functions such as <function>substr</function> do not support
      multibyte string.
     </para>
     <para>
      Multibyte extension (mbstring) has some PHP string functions
      with multibyte support (ex. <function>substr</function> supports
      <function>mb_substr</function>).
     </para>
     <para>
      Multibyte extension (mbstring) also supports 'function
      overloading' to add multibyte string functionality without
      code modification. Using function overloading, some PHP string
      functions will be oveloaded multibyte string functions.
      For example, <function>mb_substr</function> is called
      instead of <function>substr</function> if function overloading
      is enabled. Function overload makes easy to port application
      supporting only single-byte encoding for multibyte application.
     </para>
     <para>
      <literal>mbstring.func_overload</literal> in &php.ini; should be
      set some positive value to use function overloading.
      The value should specify the category of overloading functions,
      sbould be set 1 to enable mail function overloading. 2 to enable
      string functions, 4 to regular expression functions. For
      example, if is set for 7, mail, strings, regex functions should
      be overloaded. The list of overloaded functions are shown in
      below.
      <table>
      <title>Functions to be overloaded</title>
       <tgroup cols="3">
        <thead>
         <row>
          <entry>value of mbstring.func_overload</entry>
          <entry>original function</entry>
          <entry>overloaded function</entry>
         </row>
       </thead>
       <tbody>
         <row>
          <entry>1</entry>
          <entry><function>mail</function></entry>
          <entry><function>mb_send_mail</function></entry>
         </row>
         <row>
          <entry>2</entry>
          <entry><function>strlen</function></entry>
          <entry><function>mb_strlen</function></entry>
         </row>
         <row>
          <entry>2</entry>
          <entry><function>strpos</function></entry>
          <entry><function>mb_strpos</function></entry>
         </row>
         <row>
          <entry>2</entry>
          <entry><function>strrpos</function></entry>
          <entry><function>mb_strrpos</function></entry>
         </row>
         <row>
          <entry>2</entry>
          <entry><function>substr</function></entry>
          <entry><function>mb_substr</function></entry>
         </row>
         <row>
          <entry>4</entry>
          <entry><function>ereg</function></entry>
          <entry><function>mb_ereg</function></entry>
         </row>
         <row>
          <entry>4</entry>
          <entry><function>eregi</function></entry>
          <entry><function>mb_eregi</function></entry>
         </row>
         <row>
          <entry>4</entry>
          <entry><function>ereg_replace</function></entry>
          <entry><function>mb_ereg_replace</function></entry>
         </row>
         <row>
          <entry>4</entry>
          <entry><function>eregi_replace</function></entry>
          <entry><function>mb_eregi_replace</function></entry>
         </row>
         <row>
          <entry>4</entry>
          <entry><function>split</function></entry>
          <entry><function>mb_split</function></entry>
        	</row>
        </tbody>
       </tgroup>
      </table>
     </para>
   </section>

   <section id="mbstring.ja-basic">
     <title>Basics of Japanese multi-byte characters</title>
     <para>
      Most Japanese characters need more than 1 byte per character. In
      addition, several character encoding schemas are used under a
      Japanese environment. There are EUC-JP, Shift_JIS(SJIS) and
      ISO-2022-JP(JIS) character encoding. As Unicode becomes popular,
      UTF-8 is used also. To develop Web applications for a Japanese
      environment, it is important to use the character set for the
      task in hand, whether HTTP input/output, RDBMS and E-mail.
     </para>
     <para>
      <itemizedlist>
       <listitem>
        <simpara>Storage for a character can be up to six
         bytes</simpara>
       </listitem>
       <listitem>
        <simpara>
         A multi-byte character is usually twice of the width compared
         to single-byte characters. Wider characters are called
         "zen-kaku" - meaning full width, narrower characters are
         called "han-kaku" - meaning half width. "zen-kaku" characters
         are usually fixed width.
        </simpara>
       </listitem>
       <listitem>
        <simpara>
         Some character encoding defines shift(escape) sequence for
         entering/exiting multi-byte character strings.
        </simpara>
       </listitem>
       <listitem>
        <simpara>
          ISO-2022-JP must be used for SMTP/NNTP.
        </simpara>
       </listitem>
       <listitem>
        <para>
         &quot;i-mode&quot; web site is supposed to use SJIS.
        </para>
       </listitem>
      </itemizedlist>
     </para>
   </section>

   <section id="mbstring.ref">
     <title>References</title>
     <para>
      Multi-byte character encoding and its related issues are very
      complex. It is impossible to cover in sufficient detail
      here. Please refer to the following URLs and other resources for
      further readings.
      <itemizedlist>
       <listitem>
        <para>
         Unicode/UTF/UCS/etc
        </para>
        <para>
          <literal>http://www.unicode.org/</literal>
        </para>
       </listitem>
       <listitem>
        <para>
         Japanese/Korean/Chinese character
         information
        </para>
        <para>
         <literal>
         ftp://ftp.ora.com/pub/examples/nutshell/ujip/doc/cjk.inf
         </literal>
        </para>
       </listitem>
      </itemizedlist>
     </para>
   </section>
  </partintro>

&reference.mbstring.functions;

 </reference>
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