TITLE: the strictest data alignment requirements


PROBLEM: wil@ittpub.nl (Wil Evers)

Does anyone know if the draft C++ standard defines a way to find the type  
that has the most stringent alignment requirements, or can I assume using  
double here is always good enough?


RESPONSE: clamage@Eng.Sun.COM (Steve Clamage), 15 Nov 95

The DWP does not provide a portable way (that I can think of, but I may
be insufficiently clever) to find the type with the strongest alignment
requirements.

You can't assume type double has the strongest requirements. If you
make a union with all the built-in types (including some representative
function pointer types) that will probably be good enough, but is
still not guaranteed. You don't have to provide char (because it must
have the weakest requirement) or both signed and unsigned versions
of integer types (because the alignment requirements for practical
purposes must be the same). So something like this
	union Align {
		int i;
		long l;
		float f;
		double d;
		long double ld;
		void *vp;
		long *lp;
		long double* ldp;
		int (*ifp)(int);
		long double (*dfp)(long double);
	};
would probably do. I have no particular justification for omitting some
of the omitted types; you could add more if you like.

I suppose an implementation could exist for which this Align type would not
be sufficient for the static allocation trick, but I don't know of any in
practice. ("In theory, theory and practice agree; in practice, they don't".)