Question

void MyFunction(int i) throw();

it just tells the compiler that the function does not throw any exceptions.

It can’t make sure the function throw nothing, is that right?

So what’s the use of throw()

Is it redundant? Why this idea is proposed?

Answer 1

First of all, when the compiler works right, it is enforced — but at run-time, not compile-time.. A function with an empty exception specification will not throw an exception. If something happens that would create an exception escaping from it, will instead call unexpected(), which (in turn) calls abort. You can use set_unexpected to change what gets called, but about all that function is allowed to do is add extra “stuff” (e.g. cleanup) before aborting the program — it can’t return to the original execution path.

That said, at least one major compiler (VC++) parses exception specifications, but does not enforce them, though it can use empty exception specifications to improve optimization a little. In this case, an exception specification that isn’t followed can/does result in undefined behavior instead of necessarily aborting the program.