structure members of packed structures

[Hans-Peter Nilsson]

On Mon, 14 Jul 2003, Nathan Sidwell wrote:
> struct Unpacked {  int i; };
>
> struct  __attribute__ ((packed)) Packed
> {
>    char c;
>    Unpacked u;
> };
>
> where should 'u' be placed? Our current behavour is to pack it so that
> Unpacked's members are unaligned.
>
> options

> 1) continue this behaviour, but prevent taking references/address of u or
> any of its members.

Only for members whose type does not include a "packed"
qualifier, and only when used in an expression whose type also
doesn't include a packed qualifier.  For example, this should
remain valid and supported:

struct Packed s1;
struct __attribute__ ((packed)) Unpacked *p1;
p1 = &s1.u;

> 2) force u to be aligned (ignoring the packed attribute).

No, that'd be very broken.

brgds, H-P