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

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<?xml version="1.0" encoding="utf-8"?>
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<chapter xml:id="mbstring.overload" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
<title>
Function Overloading Feature
</title>
<para>
&warn.deprecated.feature-7-2-0.removed-8-0-0;
</para>
<para>
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 <function>substr</function>, which are known to
not properly handle multibyte-encoded strings.
</para>
<para>
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,
<function>mb_substr</function> is called instead of
<function>substr</function> 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.
</para>
<para>
To use function overloading, set
<literal>mbstring.func_overload</literal> 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 <function>mail</function> 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.
<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>2</entry>
<entry><function>strtolower</function></entry>
<entry><function>mb_strtolower</function></entry>
</row>
<row>
<entry>2</entry>
<entry><function>strtoupper</function></entry>
<entry><function>mb_strtoupper</function></entry>
</row>
<row>
<entry>2</entry>
<entry><function>stripos</function></entry>
<entry><function>mb_stripos</function></entry>
</row>
<row>
<entry>2</entry>
<entry><function>strripos</function></entry>
<entry><function>mb_strripos</function></entry>
</row>
<row>
<entry>2</entry>
<entry><function>strstr</function></entry>
<entry><function>mb_strstr</function></entry>
</row>
<row>
<entry>2</entry>
<entry><function>stristr</function></entry>
<entry><function>mb_stristr</function></entry>
</row>
<row>
<entry>2</entry>
<entry><function>strrchr</function></entry>
<entry><function>mb_strrchr</function></entry>
</row>
<row>
<entry>2</entry>
<entry><function>substr_count</function></entry>
<entry><function>mb_substr_count</function></entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<note>
<para>
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.
</para>
</note>
</chapter>
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