Function Overloading Feature

Warning

This feature has been DEPRECATED as of PHP 7.2.0. Relying on this feature is highly discouraged.

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.

**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
2	strtolower	mb_strtolower
2	strtoupper	mb_strtoupper
2	stripos	mb_stripos
2	strripos	mb_strripos
2	strstr	mb_strstr
2	stristr	mb_stristr
2	strrchr	mb_strrchr
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.