Is this a safe way of throwing an exception from a destructor?

Question

I know that throwing from a destructor is in general a bad idea, but I was wondering if i could use std::uncaught_exception() to safely throw from a destructor.

Consider the following RAII type:

struct RAIIType {
   ...

   ~RAIIType() {
      //do stuff..
      if (SomethingBadHappened()) {
           //Assume that if an exception is already active, we don't really need to detect this error
           if (!std::uncaught_exception()) {
               throw std::runtime_error("Data corrupted");
           }
      }
   }
};

Is this UB in c++11? Is it a bad design?

Answer 1

You have an if, did you think about the "other" condition? It can throw an exception or... do what? There's two things that can be in the other branch.

• Nothing (If nothing needs to happen when the error occurs, why throw an exception?)
• It "handles" the exception (If it can be "handled", why throw an exception?)

Now that we've established that there's no purpose to throwing an exception conditionally like that, the rest of the question is sort of moot. But here's a tidbit: NEVER THROW EXCEPTIONS FROM DESTRUCTORS. If an object throws an exception, the calling code normally checks that object in some way to "handle" the exception. If that object no longer exists, there's usually no way to "handle" the exception, meaning the exception should not be thrown. Either it's ignored, or the program makes a dump file and aborts. So throwing exceptions from destructors is pointless anyway, because catching it is pointless. With this is mind, classes assume that destructors won't throw, and virtually every class leaks resources if a destructor throws. So NEVER THROW EXCEPTIONS FROM DESTRUCTORS.