Packing of Struct Fields

Steven Schveighoffer schveiguy at
Sat Oct 17 13:42:46 UTC 2020

On 10/17/20 9:00 AM, Per Nordlöw wrote:
> On Saturday, 17 October 2020 at 12:51:21 UTC, ag0aep6g wrote:
>> c does come directly after s. The padding between b and c is part of 
>> s. If you don't want that padding, you can use `align(1)` to define S 
>> without padding. But then 75% of the ints in an S[] will be misaligned.
> I understand that. I don't want the alignment of `S` to change. I want 
> the padding after `s` in `T` to be avoided and have `c` start at 
> byte-offset 7. I don't see why this padding is needed in the case where 
> only a single (1-element array of) `S` is stored as a field inside 
> another aggregate.
> Ali's code prints:
> === Memory layout of 'T' (.sizeof: 12, .alignof: 4) ===
>     0: S s
>     8: char c
>     9: ... 3-byte PADDING

There might be some good reasons for this.

For one, what happens if you copy the s? Does it copy the c too?

For another, this is how C does it, so I would expect it to at least 
match C for compatibility.

I think it *should* be possible to do this, if it's not already, just 
with pragmas. (i.e. pack T but not S).


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