Hi, The issue that's confusing me arose from my intention of inheriting my exception classes from std::runtime_error rather than from std::exception. It seemed logical to me, as my exceptions are really runtime errors; getting something meaningful via what() also seemed like a good idea. However, this doesn't compile: #include <iostream> #include <stdexcept> #include <boost/exception/all.hpp> typedef boost::error_info<struct tag_foo_info, unsigned long> foo_info; struct foo_error : virtual boost::exception, virtual std::runtime_error { explicit foo_error(const char *const what) : std::runtime_error(what) { } explicit foo_error(const std::string& what) : std::runtime_error(what) { } }; static void foo() { BOOST_THROW_EXCEPTION(foo_error("foo error") << foo_info(42)); } int main(int argc, char *argv[]) { try { foo(); } catch (const std::exception& e) { std::cerr << boost::diagnostic_information(e); return 1; } return 0; } It says that there's no default constructor available for std::runtime_error. How do I fix this or should I use the idiomatic approach? The interesting thing is that if I erase the "virtual" keyword, the program compiles flawlessly. I wonder what is the reason for that, e.g. why the original code doesn't work and why the new code does, what are the consequences of making boost::exception and std::runtime_error base (non-virtual) classes, etc. I'm confused as the docs clearly recommends I build exception classes hierarchy using virtual inheritance. Could somebody please give me an insight into the inner workings of the library & inheritance mechanisms? Thank you in advance, Egor.