Re: Struct size
On Saturday, 19 April 2014 at 12:26:16 UTC, Andrej Mitrovic via
Digitalmars-d-learn wrote:
On 4/19/14, Lars T. Kyllingstad via Digitalmars-d-learn
wrote:
Say I have two structs, defined like this:
struct A { /* could contain whatever */ }
struct B { A a; }
My question is, is it now guaranteed that A.sizeof==B.sizeof?
The best thing to do is add a static assert and then you can
relax:
That's what I've done, but it would be nice to know the code
won't break due to some combination of platform and/or compiler
switches I didn't think to test. Anyway, I've played around a
bit, and found that a combination of struct and field alignment
*can* break my assumption:
align(1) struct A
{
char c;
align(1) int i;
}
struct B { A a; }
Now, A.sizeof is 5, while B.sizeof is 8. I'd have to add
align(1) to the declaration of B to fix it.
Re: Struct size
On 4/19/14, Lars T. Kyllingstad via Digitalmars-d-learn
wrote:
> Say I have two structs, defined like this:
>
> struct A { /* could contain whatever */ }
>
> struct B { A a; }
>
> My question is, is it now guaranteed that A.sizeof==B.sizeof?
The best thing to do is add a static assert and then you can relax:
-
struct A { }
struct B { A a; }
static assert(A.sizeof == B.sizeof);
-
As for the ABI, I don't think I've ever seen it mentioned anywhere.
Struct size
Say I have two structs, defined like this:
struct A { /* could contain whatever */ }
struct B { A a; }
My question is, is it now guaranteed that A.sizeof==B.sizeof,
regardless of how A is defined (member variable types, alignment,
etc.)? More to the point, say I have a function foo() which
looks like this:
extern(C) void foo(A* ptr, size_t len);
Is it now guaranteed that I can safely pass it a pointer to an
array of Bs? That is,
auto arr = new B[10];
foo(cast(A*) arr.ptr, arr.length);
Thanks,
Lars
