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 necessary for mbstring.
libmbfl is bundled with mbstring.
Before PHP 7.3.0, if libmbfl is already installed on the system,
--with-libmbfl[=DIR] can be specified to use
the installed library.
--disable-mbregex: Disable regular expression functions with multibyte character support.
Oniguruma is necessary for the regular
expression functions with multibyte character support.
Oniguruma is bundled with
mbstring. As of PHP 5.4.0, if
Oniguruma is already installed on the system,
--with-onig[=DIR] can be specified to
use the installed library.
As of PHP 7.4.0 --with-onig has been removed
and pkg-config is now used to detect the libonig library.
As of PHP 5.4.0 it is possible to disable the multibyte regex backtrack check by specifying --disable-mbregex-backtrack.