Re: [Boost-users] type_with_alignment<5> ?

From: John Maddock (john_at_[hidden])
Date: 2006-06-13 14:28:07

Gottlob Frege wrote:
>> I'd like type_with_alignment<> to handle sizes between 'true'
>> alignments, and/or have a way to map 'in bwetween' alignments to
>> their lower alignment.
>>
>> ie I have a struct of unknown type, but known size = 5.  What is it's
>> alignment?  You could 'punt' and say max_align, but I suggest that
>> its alignment is <= 5 (ie probably 4 for a typical platform).  ie
>> imagine that the struct might have an int as it's first member, but
>> can't have a double (assuming sizeof(double) > 5), so the alignment
>> might need to be alignment_of<int>, but can't be
>> alignment_of<double>.  Does this assumption hold true?
>>
>> So how can I map (at compile time) an integer 'n' to the closest 'x'
>> <= n where x is from the set S, and where S is the set of possible
>> alignments?

What's wrong with:

boost::alignment_of<unknown_struct>::value   ?

You can feed the result into type_with_alignment<> if that's what you want 
as well.

John.