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# LII. Multi-Byte String Functions

# Einführung

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. `mbstring` is developed to handle Japanese characters. However, many `mbstring` functions are able to handle character encoding other than Japanese.

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.

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 `mbstring.internal_encoding` to a character encoding that works with PHP.

PHP4 Character Encoding Requirements

- Per byte encoding

- Single byte characters in range of `00h-7fh` which is compatible with `ASCII`

- Multi-byte characters without `00h-7fh`

These are examples of internal character encoding that works with PHP and does NOT work with PHP.

    Character encodings work with PHP:
    ISO-8859-*, EUC-JP, UTF-8

    Character encodings do NOT work with PHP:
    JIS, SJIS

Character encoding, that does not work with PHP, may be converted with `mbstring`'s HTTP input/output conversion feature/function.

> Anmerkung: SJIS should not be used for internal encoding unless the reader is familiar with parser/compiler, character encoding and character encoding issues.

> Anmerkung: If you use databases with PHP, it is recommended that you use the same character encoding for both database and `internal encoding` for ease of use and better performance.

> If you are using PostgreSQL, it supports character encoding that is different from backend character encoding. See the PostgreSQL manual for details.

# Installation

`mbstring` is an extended module. You must enable the module with the `configure` script. Refer to the Install section for details.

The following configure options are related to the `mbstring` module.

- `--enable-mbstring` : Enable `mbstring` functions. This option is required to use `mbstring` functions.

  > Anmerkung: As of PHP 4.3.0, the option `--enable-mbstring` will be enabled by default and replaced with `--with-mbstring[=LANG]` to support Chinese, Korean and Russian language support. Japanese character encoding is supported by default. If `--with-mbstring=cn` is used, simplified chinese encoding will be supported. If `--with-mbstring=tw` is used, traditional chinese encoding will be supported. If `--with-mbstring=kr` is used, korean encoding will be supported. If `--with-mbstring=ru` is used, russian encoding will be supported. If `--with-mbstring=all` is added, all supported character encoding in mbstring will be enabled, but the binary size of PHP will be maximized because of huge Unicode character maps. Note that Chinese, Korean and Russian encoding is experimentally supported in PHP 4.3.0.

- `--enable-mbstr-enc-trans` : Enable HTTP input character encoding conversion using `mbstring` conversion engine. If this feature is enabled, HTTP input character encoding may be converted to `mbstring.internal_encoding` automatically.

  > Anmerkung: As of PHP 4.3.0, the option `--enable-mbstr-enc-trans` will be eliminated and replaced with `mbstring.encoding_translation`. HTTP input character encoding conversion is enabled when this is set to `On` (the default is `Off`).

- `--enable-mbregex` : Enable regular expression functions with multibyte character support.

# Laufzeit Konfiguration

Das Verhalten dieser Funktionen wird von Einstellungen in der `php.ini` bestimmt.

Tabelle 1. Multi-Byte String configuration options

Name | Default | Changeable
--- | --- | ---
mbstring.language | NULL | PHP_INI_ALL
mbstring.detect_order | NULL | PHP_INI_ALL
mbstring.http_input | NULL | PHP_INI_ALL
mbstring.http_output | NULL | PHP_INI_ALL
mbstring.internal_encoding | NULL | PHP_INI_ALL
mbstring.script_encoding | NULL | PHP_INI_ALL
mbstring.substitute_character | NULL | PHP_INI_ALL
mbstring.func_overload | "0" | PHP_INI_SYSTEM
mbstring.encoding_translation | "0" | PHP_INI_ALL

For further details and definition of the PHP_INI_* constants see ini_set().

Here is a short explanation of the configuration directives.

- `mbstring.language` defines default language used in mbstring. Note that this option defines `mbstring.interanl_encoding` and `mbstring.interanl_encoding` should be placed after `mbstring.language` in `php.ini`

- `mbstring.encoding_translation` enables HTTP input character encoding detection and translation into internal chatacter encoding.

- `mbstring.internal_encoding` defines default internal character encoding.

- `mbstring.http_input` defines default HTTP input character encoding.

- `mbstring.http_output` defines default HTTP output character encoding.

- `mbstring.detect_order` defines default character code detection order. See also mb_detect_order().

- `mbstring.substitute_character` defines character to substitute for invalid character encoding.

- `mbstring.func_overload`overload(replace) single byte functions by mbstring functions. mail(), ereg(), etc. are overloaded by mb_send_mail(), mb_ereg(), etc. Possible values are 0, 1, 2, 4 or a combination of them. For example, 7 for overload everything. 0: No overload, 1: Overload mail() function, 2: Overload str*() functions, 4: Overload ereg*() functions.

Web Browsers are supposed to use the same character encoding when submitting form. However, browsers may not use the same character encoding. See mb_http_input() to detect character encoding used by browsers.

If `enctype` is set to `multipart/form-data` in HTML forms, `mbstring` does not convert character encoding in POST data. The user must convert them in the script, if conversion is needed.

Although, browsers are smart enough to detect character encoding in HTML. `charset` is better to be set in HTTP header. Change `default_charset` according to character encoding.

Beispiel 1. `php.ini` setting example

    ; Set default language
    mbstring.language        = English; Set default language to English (default)
    mbstring.language        = Japanese; Set default language to Japanese

    ;; Set default internal encoding
    ;; Note: Make sure to use character encoding works with PHP
    mbstring.internal_encoding    = UTF-8  ; Set internal encoding to UTF-8

    ;; HTTP input encoding translation is enabled.
    mbstring.encoding_translation = On

    ;; Set default HTTP input character encoding
    ;; Note: Script cannot change http_input setting.
    mbstring.http_input           = pass    ; No conversion.
    mbstring.http_input           = auto    ; Set HTTP input to auto
                                    ; "auto" is expanded to "ASCII,JIS,UTF-8,EUC-JP,SJIS"
    mbstring.http_input           = SJIS    ; Set HTTP2 input to  SJIS
    mbstring.http_input           = UTF-8,SJIS,EUC-JP ; Specify order

    ;; Set default HTTP output character encoding
    mbstring.http_output          = pass    ; No conversion
    mbstring.http_output          = UTF-8   ; Set HTTP output encoding to UTF-8

    ;; Set default character encoding detection order
    mbstring.detect_order         = auto    ; Set detect order to auto
    mbstring.detect_order         = ASCII,JIS,UTF-8,SJIS,EUC-JP ; Specify order

    ;; Set default substitute character
    mbstring.substitute_character = 12307   ; Specify Unicode value
    mbstring.substitute_character = none    ; Do not print character
    mbstring.substitute_character = long    ; Long Example: U+3000,JIS+7E7E

Beispiel 2. `php.ini` setting for `EUC-JP` users

    ;; Disable Output Buffering
    output_buffering      = Off

    ;; Set HTTP header charset
    default_charset       = EUC-JP

    ;; Set default language to Japanese
    mbstring.language = Japanese

    ;; HTTP input encoding translation is enabled.
    mbstring.encoding_translation = On

    ;; Set HTTP input encoding conversion to auto
    mbstring.http_input   = auto

    ;; Convert HTTP output to EUC-JP
    mbstring.http_output  = EUC-JP

    ;; Set internal encoding to EUC-JP
    mbstring.internal_encoding = EUC-JP

    ;; Do not print invalid characters
    mbstring.substitute_character = none

Beispiel 3. `php.ini` setting for `SJIS` users

    ;; Enable Output Buffering
    output_buffering     = On

    ;; Set mb_output_handler to enable output conversion
    output_handler       = mb_output_handler

    ;; Set HTTP header charset
    default_charset      = Shift_JIS

    ;; Set default language to Japanese
    mbstring.language = Japanese

    ;; Set http input encoding conversion to auto
    mbstring.http_input  = auto

    ;; Convert to SJIS
    mbstring.http_output = SJIS

    ;; Set internal encoding to EUC-JP
    mbstring.internal_encoding = EUC-JP

    ;; Do not print invalid characters
    mbstring.substitute_character = none

# Resource Typen

Diese Erweiterung definiert keine Resource-Typen.

# Vordefinierte Konstanten

Folgende Konstanten werden von dieser Erweiterung definiert und stehen nur zur Verfügung, wenn die Erweiterung entweder statisch in PHP kompiliert oder dynamisch zur Laufzeit geladen wurde.

`MB_OVERLOAD_MAIL` (integer)

`MB_OVERLOAD_STRING` (integer)

`MB_OVERLOAD_REGEX` (integer)

# HTTP Input and Output

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.

If `enctype` for HTML form is set to `multipart/form-data`, `mbstring` does not convert character encoding in POST data. If it is the case, strings are needed to be converted to internal character encoding.

- HTTP Input

  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`.

  Beispiel 4. Disable HTTP input conversion in `php.ini`

      ;; Disable HTTP Input conversion
      mbstring.http_input = pass
      ;; Disable HTTP Input conversion (PHP 4.3.0 or higher)
      mbstring.encoding_translation = Off

  When using PHP as an Apache module, it is possible to override PHP ini setting per Virtual Host in `httpd.conf` or per directory with `.htaccess`. Refer to the Configuration section and Apache Manual for details.

- HTTP Output

  There are several ways to enable output character encoding conversion. One is using `php.ini`, another is using ob_start() with mb_output_handler() as `ob_start` callback function.

  > Anmerkung: For PHP3-i18n users, `mbstring`'s output conversion differs from PHP3-i18n. Character encoding is converted using output buffer.

Beispiel 5. `php.ini` setting example

    ;; 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

Beispiel 6. Script example

    <?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');

    ?>

# Supported Character Encodings

Currently, the following character encoding is supported by the `mbstring` module. Character encoding may be specified for `mbstring` functions' `encoding` parameter.

The following character encoding is supported in this PHP extension:

`UCS-4`, `UCS-4BE`, `UCS-4LE`, `UCS-2`, `UCS-2BE`, `UCS-2LE`, `UTF-32`, `UTF-32BE`, `UTF-32LE`, `UCS-2LE`, `UTF-16`, `UTF-16BE`, `UTF-16LE`, `UTF-8`, `UTF-7`, `ASCII`, `EUC-JP`, `SJIS`, `eucJP-win`, `SJIS-win`, `ISO-2022-JP`, `JIS`, `ISO-8859-1`, `ISO-8859-2`, `ISO-8859-3`, `ISO-8859-4`, `ISO-8859-5`, `ISO-8859-6`, `ISO-8859-7`, `ISO-8859-8`, `ISO-8859-9`, `ISO-8859-10`, `ISO-8859-13`, `ISO-8859-14`, `ISO-8859-15`, `byte2be`, `byte2le`, `byte4be`, `byte4le`, `BASE64`, `7bit`, `8bit` and `UTF7-IMAP`.

As of PHP 4.3.0, the following character encoding support will be added experimentaly : `EUC-CN`, `CP936`, `HZ`, `EUC-TW`, `CP950`, `BIG-5`, `EUC-KR`, `UHC` (`CP949`), `ISO-2022-KR`, `Windows-1251` (`CP1251`), `Windows-1252` (`CP1252`), `CP866`, `KOI8-R`.

`php.ini` entry, which accepts encoding name, accepts "`auto`" and "`pass`" also. `mbstring` functions, which accepts encoding name, and accepts "`auto`".

If "`pass`" is set, no character encoding conversion is performed.

If "`auto`" is set, it is expanded to "`ASCII,JIS,UTF-8,EUC-JP,SJIS`".

See also mb_detect_order()

> Anmerkung: "Supported character encoding" does not mean that it works as internal character code.

# Overloading PHP string functions with multi byte string functions

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 substr() do not support multibyte string.

Multibyte extension (mbstring) has some PHP string functions with multibyte support (ex. substr() supports mb_substr()).

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, mb_substr() is called instead of substr() if function overloading is enabled. Function overload makes easy to port application supporting only single-byte encoding for multibyte application.

`mbstring.func_overload` 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.

Tabelle 2. Functions to be overloaded

value of mbstring.func_overload | original function | overloaded function
--- | --- | ---
1 | mail() | mb_send_mail()
2 | strlen() | mb_strlen()
2 | strpos() | mb_strpos()
2 | strrpos() | mb_strrpos()
2 | substr() | mb_substr()
4 | ereg() | mb_ereg()
4 | eregi() | mb_eregi()
4 | ereg_replace() | mb_ereg_replace()
4 | eregi_replace() | mb_eregi_replace()
4 | split() | mb_split()

# Basics of Japanese multi-byte characters

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.

- Storage for a character can be up to six bytes

- 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.

- Some character encoding defines shift(escape) sequence for entering/exiting multi-byte character strings.

- ISO-2022-JP must be used for SMTP/NNTP.

- "i-mode" web site is supposed to use SJIS.

# References

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.

- Unicode/UTF/UCS/etc

  `http://www.unicode.org/`

- Japanese/Korean/Chinese character information

  `ftp://ftp.ora.com/pub/examples/nutshell/ujip/doc/cjk.inf`

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