I am looking for an alternative to C-style union. boost::variant is one such option. Is there anything in std C++ ?
As several commenters said: No, there is no Boost Variant-alike in standard C++. Maybe in a few years there will be, but why wait--use Boost Variant today!
Edit (four years later, 2016): In C++17 there will be
std::variant. Similar but not identical to
boost::variant. So when your compiler supports C++17, you will have a solution in the standard library.