http://digitalmars.com/d/2.0/attribute.html#align

"align by itself sets it to the default, which matches the default member alignment of the companion C compiler."
OK!

"align(Integer): Integer specifies the alignment which matches the behavior of the companion C compiler when non-default alignments are used"
I don't really understand that sentence.

"struct S
{   align(4) byte a;	// placed at offset 0
    align(4) byte b;	// placed at offset 1
}"

So those align(4)s are completely useless since the default alignment is chosen anyways?



"align (1) struct S
{   byte a;	// placed at offset 0
    byte[3] filler1;
    byte b;	// placed at offset 4
    byte[3] filler2;
}"

This is just as I would expect but this leaves no chance to specify alignment for individual members, does it?

Trass3r:
> So those align(4)s are completely useless since the default alignment is chosen anyways?

On 64 bit CPUs/systems the alignment can be 8, so if you ask for 4 you get 4 instead of 8.


> This is just as I would expect but this leaves no chance to specify alignment for individual members, does it?

You can put the alignment to single members.

I suggest you to print the .alignof attribute of all your members in your experiments, so you can answer to your own questions in a quick way.

Bye,
bearophile

> I suggest you to print the .alignof attribute of all your members in your experiments, so you can answer to your own questions in a quick way.

I meant the .offsetof attribute, sorry.

Trass3r wrote:
> http://digitalmars.com/d/2.0/attribute.html#align
> 
> "align by itself sets it to the default, which matches the default member alignment of the companion C compiler."
> OK!
> 
> "align(Integer): Integer specifies the alignment which matches the behavior of the companion C compiler when non-default alignments are used"
> I don't really understand that sentence.
<snip>

Basically, it means that the member is aligned on n-byte boundaries in whatever way the companion C compiler does if instructed to.

However, there's no statement I can find of what's supposed to happen if the companion C compiler doesn't support alignment control at the level where it is used.

http://d.puremagic.com/issues/show_bug.cgi?id=3183
(marked as fixed, but it seems it isn't really)
http://www.digitalmars.com/d/archives/digitalmars/D/Spec_of_align_attribute_is_a_mess_88129.html

Stewart.