John Gateley writes: > I need to compute the offset of a data member at compile time. > The class has virtual functions, and so the offsetof macro does > not work (why?). Because it's a non-POD type. See Section 9, Classes: << A POD-struct is an aggregate class that has no non-static data members of type pointer to member, non-POD-struct, non-POD-union (or array of such types) or reference, and has no user-defined copy assignment operator and no user-defined destructor. Similarly, a POD-union is an aggregate union that has no non-static data members of type pointer to member, non-POD-struct, non-POD-union (or array of such types) or reference, and has no user-defined copy assignment operator and no user-defined destructor. A POD class is a class that is either a POD-struct or a POD-union. >> Section 18.1 Para 5: << The macro offsetof accepts a restricted set of type arguments in this International Standard. type shall be a POD structure or a POD union (clause 9). The result of applying the offsetof macro to a field that is a static data member or a function member is undefined. SEE ALSO: subclause 5.3.3, Sizeof, subclause 5.7, Additive operators, subclause 12.5, Free store, and ISO C subclause 7.1.6. 18.2 Implementation properties [lib.support.limits] >> > Is there a way to do this? No. Consider what happens with multiple and virtual inheritance. Andrew.
