C++: [[maybe_noreturn]]

Question

As far as I am aware, there is no [[maybe_noreturn]] attribute in C++.

I have a function which looks like this:

void func() {
    try {
        do_something();
    } catch (const std::exception& e) {
        std::exit(1);
    }
}

If I would mark func as [[noreturn]] I'd run into UB for the happy case. Is it UB when I do not return from a function that is not marked as [[noreturn]]?

Or are there other language constructs, compiler extensions or libraries that implement something like [[maybe_noreturn]]?

`[[noreturn]]` may only be used when the function is guaranteed to not return. — JohnFilleau, Feb 07 '22 at 15:46
What would you like `[[maybe_noreturn]]` to signify? Is this to signal something to the compiler? To the library user? How would I, as another developer, change how I interact with the function if you mark it `[[maybe_noreturn]]`? — JohnFilleau, Feb 07 '22 at 15:46
Aren't functions essentially `maybe_noreturn` by default unless you add a `noexcept` specifier? — Nathan Pierson, Feb 07 '22 at 15:52
`noexcept` functions are very much "maybe_noreturn". In fact, they are more likely to terminate than other functions since any exception escaping them will cause them to terminate. — eerorika, Feb 07 '22 at 15:59

eerorika · Accepted Answer · 2022-02-07T16:19:39.227

Is it UB when I do not return from a function that is not marked as [[noreturn]]?

No, it's well defined to terminate the program from a function regardless whether it has [[noreturn]] attribute or not. Using [[noreturn]] is optional when it is appropriate - i.e. when a function terminates unconditionally - but it is always recommended in such cases.

No such attribute as [[maybe_noreturn]] is needed. If it were necessary, then you would find that you would have to declare any function potentially calling [[maybe_noreturn]] function to also be [[maybe_noreturn]], and then functions that call those functions, all the way to the top of the call chain.

C++: [[maybe_noreturn]]

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