[cfe-dev] c++11's alignas() ignored inside #pragma pack

[Richard Smith]

On Tue, Jul 22, 2014 at 1:03 PM, jahanian <fjahanian at apple.com> wrote:

> Implementation says that it is intentional:
>
>   // The maximum field alignment overrides the aligned attribute.
>   if (!MaxFieldAlignment.isZero()) {
>     FieldAlign = std::min(FieldAlign, MaxFieldAlignment);
>     UnpackedFieldAlign = std::min(UnpackedFieldAlign, MaxFieldAlignment);
>   }
> - Fariborz
>

I too find this very surprising. Does this match GCC / MSVC behavior for
#pragma pack? I don't think it matches __attribute__((packed)).


> On Jul 22, 2014, at 11:04 AM, jahanian <fjahanian at apple.com> wrote:
>
> This test shows that alignas() is ignored when used with #pragma.
> Is this intentional behavior?
>
> #pragma pack(push, 1)
> struct S1 { char a; short b; double c; alignas(32) double d; char e;
> double f; };
> #pragma pack(pop)
>
> int main()
> {
>  return sizeof(struct S1);
> }
>
> - Thanks, Fariborz
>
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