In xpressive, I'm trying to follow the recommended use of Boost.Exception and use virtual inheritance in my exception class, regex_error. I'm also trying to hew as closely as possible to the standard, which says that regex_error should inherit from std::runtime_error. However, this simple use of Boost.Exception does not compile: #include <string> #include <exception> #include <boost/throw_exception.hpp> #include <boost/exception/exception.hpp> struct regex_error : virtual std::runtime_error , virtual boost::exception { explicit regex_error(std::string const& what) : std::runtime_error(what) {} }; int main() { boost::throw_exception(regex_error("what")); } On VC9, I get the following:
C:\boost\org\trunk\boost/exception/exception.hpp(400) : error C2512: 'std::runtime_error::runtime_error' : no appropriate default constructor available
The trouble is that std::runtime_error does not have a default constructor, and that boost::throw_exception doesn't simply throw the exception passed to it; it throws an object of type of clone_impl<regex_error>. Because of the virtual inheritance, clone_impl needs to call std::runtime_error's directly, but it doesn't. It can't know to do that in general. What is the recommended practice here? <aside> It actually doesn't seem to be particularly useful in this case to use virtual inheritance because std::runtime_error inherits from std::exception non-virtually. In order to avoid the pitfall described here <http://tinyurl.com/yb2jpns>, it seems *ever* exception type in the hierarchy needs to use virtual inheritance, and that unfortunately is not the case for the standard exception hierarchy. </aside> -- Eric Niebler BoostPro Computing http://www.boostpro.com