While there are many languages in which every necessary character can be represented by a one-to-one mapping to an 8-bit value, there are also several languages which require so many characters for written communication that they cannot be contained within the range a mere byte can code (A byte is made up of eight bits. Each bit can contain only two distinct values, one or zero. Because of this, a byte can only represent 256 unique values (two to the power of eight)). Multibyte character encoding schemes were developed to express more than 256 characters in the regular bytewise coding system.
When you manipulate (trim, split, splice, etc.) strings encoded in a multibyte encoding, you need to use special functions since two or more consecutive bytes may represent a single character in such encoding schemes. Otherwise, if you apply a non-multibyte-aware string function to the string, it probably fails to detect the beginning or ending of the multibyte character and ends up with a corrupted garbage string that most likely loses its original meaning.
mbstring provides multibyte specific string functions that help you deal with multibyte encodings in PHP. In addition to that, mbstring handles character encoding conversion between the possible encoding pairs. mbstring is designed to handle Unicode-based encodings such as UTF-8 and UCS-2 and many single-byte encodings for convenience (listed below).
Encodings of the following types are safely used with PHP.
A singlebyte encoding,
A multibyte encoding,
These are examples of character encodings that are unlikely to work with PHP.
JIS, SJIS, ISO-2022-JP, BIG-5
Although PHP scripts written in any of those encodings might not work, especially in the case where encoded strings appear as identifiers or literals in the script, you can almost avoid using these encodings by setting up the mbstring's transparent encoding filter function for incoming HTTP queries.
Note: It's highly discouraged to use SJIS, BIG5, CP936, CP949 and GB18030 for the internal encoding unless you are familiar with the parser, the scanner and the character encoding.
Note: If you are connecting to a database with PHP, it is recommended that you use the same character encoding for both the database and the internal encoding for ease of use and better performance.
If you are using PostgreSQL, the character encoding used in the database and the one used in PHP may differ as it supports automatic character set conversion between the backend and the frontend.
mbstring is a non-default extension. This means it is not enabled by default. You must explicitly enable the module with the configure option. See 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.
libmbfl is necesarry for mbstring. libmbfl is bundled with mbstring. If libmbfl is already installed on the system, --with-libmbfl[=DIR] can be specified to use the installed library.
As of PHP 4.3.0, mbstring extension provides enhanced support for Simplified Chinese, Traditional Chinese, Korean, and Russian in addition to Japanese.
For PHP 4.3.3 or before, To enable that feature, you will have to supply either one of the following options to the LANG parameter of --enable-mbstring=LANG; --enable-mbstring=cn for Simplified Chinese support, --enable-mbstring=tw for Traditional Chinese support, --enable-mbstring=kr for Korean support, --enable-mbstring=ru for Russian support, and --enable-mbstring=ja for Japanese support (default). To enable all supported encoding, use --enable-mbstring=all.
Note: As of PHP 4.3.4, all supported encoding by libmbfl is enabled with --enable-mbstring.
--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.
Note: As of PHP 4.3.0, the option --enable-mbstr-enc-trans was eliminated and replaced with the runtime setting mbstring.encoding_translation. HTTP input character encoding conversion is enabled when this is set to On (the default is Off).
--disable-mbregex: Disable regular expression functions with multibyte character support.
The behaviour of these functions is affected by settings in php.ini.
| Name | Default | Changeable | Changelog |
|---|---|---|---|
| mbstring.language | "neutral" | PHP_INI_PERDIR | Available since PHP 4.3.0. |
| mbstring.detect_order | NULL | PHP_INI_ALL | Available since PHP 4.0.6. |
| mbstring.http_input | "pass" | PHP_INI_ALL | Available since PHP 4.0.6. |
| mbstring.http_output | "pass" | PHP_INI_ALL | Available since PHP 4.0.6. |
| mbstring.internal_encoding | NULL | PHP_INI_ALL | Available since PHP 4.0.6. |
| mbstring.script_encoding | NULL | PHP_INI_ALL | Available since PHP 4.3.0. |
| mbstring.substitute_character | NULL | PHP_INI_ALL | Available since PHP 4.0.6. |
| mbstring.func_overload | "0" | PHP_INI_PERDIR | PHP_INI_SYSTEM in PHP <= 4.2.3. Available since PHP 4.2.0. |
| mbstring.encoding_translation | "0" | PHP_INI_PERDIR | Available since PHP 4.3.0. |
| mbstring.strict_detection | "0" | PHP_INI_ALL | Available since PHP 5.1.2. |
Here's a short explanation of the configuration directives.
The default national language setting (NLS) used in mbstring. Note that this option automagically defines mbstring.internal_encoding and mbstring.internal_encoding should be placed after mbstring.language in php.ini
Enables the transparent character encoding filter for the incoming HTTP queries, which performs detection and conversion of the input encoding to the internal character encoding.
Defines the default internal character encoding.
Defines the default HTTP input character encoding.
Defines the default HTTP output character encoding.
Defines default character code detection order. See also mb_detect_order().
Defines character to substitute for invalid character encoding.
Overloads a set of single byte functions by the mbstring counterparts. See Function overloading for more information.
Enables the strict encoding detection.
According to the » HTML 4.01 specification, Web browsers are allowed to encode a form being submitted with a character encoding different from the one used for the page. See mb_http_input() to detect character encoding used by browsers.
Although popular browsers are capable of giving a reasonably accurate guess to the character encoding of a given HTML document, it would be better to set the charset parameter in the Content-Type HTTP header to the appropriate value by header() or default_charset ini setting.
Example#1 php.ini setting examples
; Set default language
mbstring.language = Neutral; Set default language to Neutral(UTF-8) (default)
mbstring.language = English; Set default language to English
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
Example#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
Example#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
This extension has no resource types defined.
The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.
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.
Note: In PHP 4.3.2 or earlier versions, there was a limitation in this functionality that mbstring does not perform character encoding conversion in POST data if the enctype attribute in the form element is set to multipart/form-data. So you have to convert the incoming data by yourself in this case if necessary.
Beginning with PHP 4.3.3, if enctype for HTML form is set to multipart/form-data and mbstring.encoding_translation is set to On in php.ini the POST'ed variables and the names of uploaded files will be converted to the internal character encoding as well. However, the conversion isn't applied to the query keys.
There is no way to control HTTP input character conversion from a PHP script. To disable HTTP input character conversion, it has to be done in php.ini.
Example#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 those settings in each Virtual Host directive in httpd.conf or per directory with .htaccess. Refer to the Configuration section and Apache Manual for details.
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 the ob_start callback function.
Note: PHP3-i18n users should note that mbstring's output conversion differs from PHP3-i18n. Character encoding is converted using an output buffer.
Example#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
Example#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');
?>
Currently the following character encodings are supported by the mbstring module. Any of those Character encodings can be specified in the encoding parameter of mbstring functions.
The following character encodings are supported in this PHP extension:
Any php.ini entry which accepts an encoding name can also use the values "auto" and "pass". mbstring functions which accept an encoding name can also use the value "auto".
If "pass" is set, no character encoding conversion is performed.
If "auto" is set, it is expanded to the list of encodings defined per the NLS. For instance, if the NLS is set to Japanese, the value is assumed to be "ASCII,JIS,UTF-8,EUC-JP,SJIS".
See also mb_detect_order()
You might often find it difficult to get an existing PHP application to work in a given multibyte environment. This happens because most PHP applications out there are written with the standard string functions such as substr(), which are known to not properly handle multibyte-encoded strings.
mbstring supports a 'function overloading' feature which enables you to add multibyte awareness to such an application without code modification by overloading multibyte counterparts on the standard string functions. For example, mb_substr() is called instead of substr() if function overloading is enabled. This feature makes it easy to port applications that only support single-byte encodings to a multibyte environment in many cases.
To use function overloading, set mbstring.func_overload in php.ini to a positive value that represents a combination of bitmasks specifying the categories of functions to be overloaded. It should be set to 1 to overload the mail() function. 2 for string functions, 4 for regular expression functions. For example, if it is set to 7, mail, strings and regular expression functions will be overloaded. The list of overloaded functions are shown below.
| 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() |
| 2 | strtolower() | mb_strtolower() |
| 2 | strtoupper() | mb_strtoupper() |
| 2 | substr_count() | mb_substr_count() |
| 4 | ereg() | mb_ereg() |
| 4 | eregi() | mb_eregi() |
| 4 | ereg_replace() | mb_ereg_replace() |
| 4 | eregi_replace() | mb_eregi_replace() |
| 4 | split() | mb_split() |
Note: It is not recommended to use the function overloading option in the per-directory context, because it's not confirmed yet to be stable enough in a production environment and may lead to undefined behaviour.
Japanese characters can only be represented by multibyte encodings, and multiple encoding standards are used depending on platform and text purpose. To make matters worse, these encoding standards differ slightly from one another. In order to create a web application which would be usable in a Japanese environment, a developer has to keep these complexities in mind to ensure that the proper character encodings are used.
Multibyte character encoding schemes and their related issues are fairly complicated, and are beyond the scope of this documentation. Please refer to the following URLs and other resources for further information regarding these topics.
Unicode materials
Japanese/Korean/Chinese character information