I just opened a project in QT Creator 4.9 and in the application .cpp I get a warning that this function could include attribute 'noreturn', but I have not found how to declare this. I find examples of code such as:

[[ noreturn ]] void f() {
throw "error";
// OK

void q [[ noreturn ]] (int i) {
// behavior is undefined if called with an argument <= 0
if (i > 0) {
throw "positive";

but no clue as to where this goes--in the function .cpp? or the main.cpp? before the function? within the function?
and I'm not at all familiar with the syntax [[ something ]].

Or does it even matter whether the attribute is declared or not?