[Bug c/51568] Enum value is not extracted properly via a union

[rearnsha at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51568

--- Comment #2 from Richard Earnshaw <rearnsha at gcc dot gnu.org> 2011-12-15 
17:27:19 UTC ---
(In reply to comment #1)
> On linux sizeof (struct rec) is 7, so how do you expect an unsigned (size = 4)
> to hold the entire value?
> 
> If you want a packed enum, you need to specify the packed on the element
> declaration, not just on the overall structure:
> 
> struct rec {
>   unsigned short w;
>   unsigned char  c;
>   enum en e __attribute__((packed));
> } __attribute__((packed));

Actually that doesn't work.  The only ways to pack the enum into 8 bits are to
either:

1) Use -fshort-enums (ABI change)
2) Use a bitfield expression in your struct.

struct rec {
  unsigned short w;
  unsigned char  c;
  enum en e:8;
} __attribute__((packed));

Sorry for the confusion.