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The variable declared by the exception-declaration, of type cv T or cv T&, is initialized from the exception object, of type E, as follows:
  — if T is a base class of E, the variable is copy-initialized from the corresponding base class subobject of the exception object;
  — otherwise, the variable is copy-initialized from the exception object.

Because the variable declared by the exception-declaration is copy-initialized, it is possible to slice the exception object as part of the copy operation, losing valuable exception information and leading to incorrect error recovery. For more information about object slicing, see OOP51-CPP. Do not slice derived objects. Further, if the copy constructor of the exception object throws an exception, the copy initialization of the exception-declaration object results in undefined behavior. (See ERR60-CPP. Exception objects must be nothrow copy constructible for more information.)

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