Is that why some structs have "char reserved[16]" data members? I think I saw this in NGINX, though that might have been to allow module compatibility between the open source offering and the paid version.
Yes, that slightly improves ABI flexibility, though the fact that callers can still access fields limits that.
An alternative is to make the only member `char opaque[16]` (IIRC some locale-related thing in glibc does this, also I think libpng went through a transition of some sort related to this?), but calculating the size can be difficult outside of trivial cases since you can't use sizeof/offsetof.
An alternative is to make the only member `char opaque[16]` (IIRC some locale-related thing in glibc does this, also I think libpng went through a transition of some sort related to this?), but calculating the size can be difficult outside of trivial cases since you can't use sizeof/offsetof.