On 10/06/10 13:19, Larry Evans wrote:
On 10/06/10 13:05, Larry Evans wrote: [snip]
A copy of the code posted here:
http://article.gmane.org/gmane.comp.lib.boost.devel/209212
followed by: [snip] Further experimentation resulted in the attached which produces output:
sizeof(A)=32 sizeof(B)=56 sizeof(A_pairs)=56 sizeof(A_bools)=40 sizeof(bools_A)=32 sizeof(chars_A)=32
So, gathering all tags at start (bools_A and chars_A) saves the most space.
The reason sizeof(A) == sizeof(bools_A) is that the 4 bools use the padding following the int A::a. IOW, bools_A puts the 4 bools where the int A::a is located, followed by the int. Hence, no extra space is needed. Adding 1 extra bool at the start causes the sizeof(bools_A) to jump by 8. This is shown by output of the attached: alignment_of<A>::value=8 sizeof(A)=32 sizeof(B)=56 sizeof(Atags)=56 sizeof(tagsA)=56 sizeof(A_bools)=40 sizeof(bools_A)=32 sizeof(bools)=4 sizeof(int)=4 alignment_of<bools>::value=1