regex_traits

namespace boost{

template <class charT, class implementationT = sensible_default_choice>
struct regex_traits : public implementationT
{
   regex_traits() : implementationT() {}
};

template <class charT>
struct c_regex_traits;

template <class charT>
struct cpp_regex_traits;

template <class charT>
struct w32_regex_traits;

} // namespace boost

Description

The class regex_traits is just a thin wrapper around an actual implemention class, which may be one of:

c_regex_traits: this class is deprecated, it wraps the C locale, and is used as the default implementation when the platform is not Win32, and the C++ locale is not available.
cpp_regex_traits: the default traits class for non-Win32 platforms, allows the regex class to be imbued with a std::locale instance.
w32_regex_traits: the default traits class implementation on Win32 platforms, allows the regex class to be imbued with an LCID.

The default behavior can be altered by defining one of the following configuration macros in boost/regex/user.hpp

BOOST_REGEX_USE_C_LOCALE: makes c_regex_traits the default.
BOOST_REGEX_USE_CPP_LOCALE: makes cpp_regex_traits the default.

All these traits classes fulfil the traits class requirements.