9 Declarations [dcl.dcl]

9.12 Attributes [dcl.attr]

9.12.9 Noreturn attribute [dcl.attr.noreturn]

The attribute-token noreturn specifies that a function does not return.
It shall appear at most once in each attribute-list and no attribute-argument-clause shall be present.
The attribute may be applied to the declarator-id in a function declaration.
The first declaration of a function shall specify the noreturn attribute if any declaration of that function specifies the noreturn attribute.
If a function is declared with the noreturn attribute in one translation unit and the same function is declared without the noreturn attribute in another translation unit, the program is ill-formed, no diagnostic required.
If a function f is called where f was previously declared with the noreturn attribute and f eventually returns, the behavior is undefined.
The function may terminate by throwing an exception.
— end note
Recommended practice: Implementations should issue a warning if a function marked [[noreturn]] might return.
[[ noreturn ]] void f() {
  throw "error";                // OK

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