Re: align(n) outside struct useless?

2017-02-20 Thread kinke via Digitalmars-d-learn 

On Monday, 20 February 2017 at 22:45:09 UTC, Adam D. Ruppe wrote:

I don't
believe it does anything (except perhaps pad bytes again) for a 
stack-defined struct.


LDC does respect explicit type-alignments when allocating 
instances on the stack. The instances are obviously padded to 
their full size.

Re: align(n) outside struct useless?

2017-02-20 Thread Adam D. Ruppe via Digitalmars-d-learn 
On Monday, 20 February 2017 at 20:45:27 UTC, Michael Coulombe 
wrote:
I can't figure out how to set the alignment of a struct using 
align(n) on the outside of the struct.


align(n) on the outside of a struct will pad the struct as a 
whole to meet that size requirement. So it changes the sizeof and 
only really aligns when you have an array of the structs. I don't 
 believe it does anything (except perhaps pad bytes again) for a 
stack-defined struct.


align on the inside will shuffle the padding around in between 
members or pushing it to the end.


You'll likely want BOTH align, inside and outside, if you want to 
get a packed array of packed structs...

Re: align(n) outside struct useless?

2017-02-20 Thread Ali Çehreli via Digitalmars-d-learn 

On 02/20/2017 12:45 PM, Michael Coulombe wrote:

I can't figure out how to set the alignment of a struct using align(n)
on the outside of the struct. Only align on the fields (default or
annotated) seems to work. I get the same results back to at least DMD
2.065... Is this a bug or am I using it wrong?


However, it works correctly:

enum A = 32;

align(A)
struct S {
char c;
}

static assert(S.sizeof == A);

Ali

align(n) outside struct useless?

2017-02-20 Thread Michael Coulombe via Digitalmars-d-learn 
I can't figure out how to set the alignment of a struct using 
align(n) on the outside of the struct. Only align on the fields 
(default or annotated) seems to work. I get the same results back 
to at least DMD 2.065... Is this a bug or am I using it wrong?


align(32) struct A { ubyte padding; }
pragma(msg, A.alignof); => 1

align(32) struct B { align(32) ubyte padding; }
pragma(msg, B.alignof); => 32

struct C { align(32) ubyte padding; }
pragma(msg, C.alignof); => 32

align(32) struct D { int padding; }
pragma(msg, D.alignof); => 4