On Sunday, 26 March 2017 at 06:38:59 UTC, zabruk70 wrote:

oh sorry sorry - mistyping

ok. DMD use padding, so for real container.sizeof
i should use lastMemeber.offsetof+lastMemeber.sizeof

On Sunday, 26 March 2017 at 06:45:13 UTC, ketmar wrote:
> yes. you have a typo in second `writefln`: S1 instead of S2. ;-)

thank you.
another question, related to my first post:

why size of S2.b1 and S2.b2 still 3, not 4?

am i right: then align applied to members, compiler not change size of members, just make padding, so CONTAINER size changes?

if so (because size of S2.b1 and S2.b2 still is 3 in my code),
then adding align(1) outside of union must not change zise of union, but size of some comainer more upper level.

zabruk70 wrote:

> On Sunday, 26 March 2017 at 06:45:13 UTC, ketmar wrote:
>> yes. you have a typo in second `writefln`: S1 instead of S2. ;-)
>
> thank you.
> another question, related to my first post:
>
> why size of S2.b1 and S2.b2 still 3, not 4?
>
> am i right: then align applied to members, compiler not change size of members, just make padding, so CONTAINER size changes?

yes. compiler is not allowed to mess with data types of the known size. ;-) and you are right: it doesn't have to. it just inserts dummy anonymous (and unused) bytes into struct/union to satisfy alignment requirements.


> if so (because size of S2.b1 and S2.b2 still is 3 in my code),
> then adding align(1) outside of union must not change zise of union, but size of some comainer more upper level.

nope, it changes size of the union itself. padding bytes *are* included in union, so `myunion.sizeof` includes 'em too.

i.e. what compiler does (roughly) is inserting anonymous fields of the appropriate size *into* the container. for "inner" aligning compiler inserts anonymous fields *between* other fields. for "outer" aligning compiler just appends anonymous field at the *end* of a data type, so data type size will met align requirements.

On Sunday, 26 March 2017 at 07:18:14 UTC, ketmar wrote:
> i.e. what compiler does (roughly) is inserting anonymous fields of the appropriate size *into* the container. for "inner" aligning compiler inserts anonymous fields *between* other fields. for "outer" aligning compiler just appends anonymous field at the *end* of a data type, so data type size will met align requirements.

Big thank!!