throw without arguments for failure signalling

Is it ok to just call throw; from constructor if something goes awry, and you have no idea how to recover?

The idea is to let the app crash with a dump, as the state is unknown. Or should you always specify an argument?

From MSDN I only found that it rethrows if there is no argument, but开发者_StackOverflow no idea what happens if there is no initial exception to rethrow.

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No. throw; is a special syntax that re-throws current exception. It only makes sense inside catch blocks (or code called from one) to continue propagating the exception.

Just use:

#include <stdexcept>
...
throw std::runtime_error("some description");

or even just

throw "some description";

but the later is uglier to handle and just generally frowned upon.

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If there's no exception currently being processed throw; will lead to terminate() being called immediately and that will end your program abnormally. That is not very convenient - you'll have less information about what happened compared to throwing a meaningful exception. You could have thrown a meaningful exception, catch it at the top level (like main()), write some diagnostics and then end the program.

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An ASSERT might make your life easier to dignose what's going wrong

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While technically you can call it, it won't do what you'd like.

The simplest solution is to call throw std::runtime_exception("thrown from Foo");, which at the same time gives some feedback about what was going on.

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When you say "no idea how to recover" what you mean I presume is that at this point you do not know how to handle the error?

Perhaps you are not getting the point of exceptions. You throw information: that the exception occurred and why. The call-stack is then unwound to the point where it can be handled. At that point in the code we know how, if possible, to recover.

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Technically, you can do that because throw without argument and without an active exception just calls terminate() which by default calls abort(). I prefer calling abort() directly, it requires less cognitive effort to recognize what is going on.