align(n) not working as expected

[Robert Jacques]

On Tue, 28 Dec 2010 00:32:37 -0700, %u <wfunction at hotmail.com> wrote:

> Hi,
>
> I'm not sure if I'm doing something wrong, but it seems like struct  
> alignment
> isn't really working. (I just found out that I'm not supposed to post  
> this on
> the digitalmars.D.bugs newsgroup, so I'm posting it here.)
>
> When I execute this code:
>
>  struct Temp
>  {
>   ubyte x;
>   align(16) ubyte y;
>  }
>  auto o = Temp();
>  std.stdio.writefln("Address of aligned fields: %#x, %#x",  
> cast(size_t)&o.x,
> cast(size_t)&o.y);
>
> I get these addresses:
>  0x18fd00, 0x18fd01
> the second of which is not aligned on a 16-byte boundary.
>
>
> Am I doing something wrong, or is this a bug?
>
> Thank you!

As per the docs, align behaves in the manner of the companion C++ compile.  
DMC only defines align(1) and align(4), so they're the only two that work.  
So this isn't a bug per say, but more than one of us has asked for  
align(8)/align(16) support. (or at least a compile time warning). But  
there's several technical/performance issues with maintaining alignment  
different from the underlying OS. I'd also recommend D.learn for questions  
like these.