Exception specification when overriding a virtual function?

If a class 开发者_StackOverflowinherits from another and overrides a virtual function, how must the exception-specification for the derived (overridden) function be related to the base function?

Is that is must be at least as restrictive? right? or others?

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Yes, it must be at least as restrictive (§15.4/3):

If a virtual function has an exception-specification, all declarations, including the definition, of any function that overrides that virtual function in any derived class shall only allow exceptions that are allowed by the exception-specification of the base class virtual function.

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It is $15.4 p.5 in http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf: "If a virtual function has an exception-specification, all declarations, including the definition, of any function that overrides that virtual function in any derived class shall only allow exceptions that are allowed by the exception-specification of the base class virtual function"