Re: [boost] no return statement in function returning non-void

From: Andrew Koenig (ark-mlist_at_[hidden])
Date: 2007-05-01 09:38:58

> Isn't it odd that this nonsense is legal c++?

Yes, sort of.  Consider:

        double foo(blah blah blah) {
                blah blah blah
                if (x >= 0)
                        return std::sqrt(x);
                throw std::domain_error("x was negative in foo");
        }

Here static analysis can tell you that control can never reach the }.  But
what if we put the throw into a separately compiled function?

                if (x >= 0)
                        return std::sqrt(x);
                throw_domain_error("x was negative in foo");

Now the programmer may know, even though the compiler cannot, that control
still cannot reach the }.  What would have standard do?  Force the
programmer to insert a return statement that the programmer knows can never
be executed?

Worse: The C89 standard allows this:

        double f() { /* no return */ }

        int main() { f(); return 0; }

In other words, a C function that claims to return non-void is allowed to
fall off the end as long as its caller does not attempt to use the
function's value.  Which means that if C++ required a function that returns
non-void to throw an exception when falling off the end, it would introduce
a C incompatibility.

So maybe I'm agreeing that it's odd--but at least there's a reason for it.