RAII vs. exceptions

Question

The more we use RAII in C++, the more we find ourselves with destructors that do non-trivial deallocation. Now, deallocation (finalization, however you want to call it) can fail

Answer 1

You can tell whether there is currently an exception in flight (e.g. we are between the throw and catch block performing stack unwinding, perhaps copying exception objects, or similar) by checking

bool std::uncaught_exception()

If it returns true, throwing at this point will terminate the program, If not, it's safe to throw (or at least as safe as it ever is). This is discussed in Section 15.2 and 15.5.3 of ISO 14882 (C++ standard).

This doesn't answer the question of what to do when you hit an error while cleaning up an exception, but there really aren't any good answers to that. But it does let you distinguish between normal exit and exceptional exit if you wait to do something different (like log&ignore it) in the latter case, rather than simply panicing.