Boost Exception

namespace
boost
    {
    template <class T>
    exception_ptr clone_exception( T const & e );
    }

T must be polymorphic.

If enable_exception_cloning() was not used at the time the exception object was passed to throw, the returned exception_ptr refers to an instance of unknown_exception. In this case, if the original exception object derives from boost::exception, then the boost::exception sub-object of the unknown_exception object is initialized by the boost::exception copy constructor;
Otherwise, if the attempt to clone the exception results in a std::bad_alloc exception, the returned exception_ptr refers to an instance of std::bad_alloc;
Otherwise, the returned exception_ptr refers to a copy of e.

It is unspecified whether the return values of two successive calls to clone_exception() refer to the same exception object.