9 Declarations [dcl.dcl]

9.12 Attributes [dcl.attr]

9.12.11 Noreturn attribute [dcl.attr.noreturn]

1
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The attribute-token noreturn specifies that a function does not return.
No attribute-argument-clause shall be present.
The attribute may be applied to a function or a lambda call operator.
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.
2
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If a function f is invoked where f was previously declared with the noreturn attribute and that invocation eventually returns, the behavior is runtime-undefined.
[Note 1: 
The function can terminate by throwing an exception.
— end note]
3
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Recommended practice: Implementations should issue a warning if a function marked [[noreturn]] might return.
The value of a has-attribute-expression for the noreturn attribute should be 0 unless the implementation can issue such warnings.
4
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[Example 1: [[ 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]