Re: enum may be signed

[grischka]

Stefan Monnier wrote:
> > +  enum symbol_redirect redirect : 3;
>
> > Note that this breaks with compilers where enums can be signed (e.g. MSVC),
> > Because value 4 doesn't fit into 3 bits (signed), it is read as -4 and
> > breaks related switch statements (e.g. data.c:set_internal)
>
> Interesting.  I didn't know about that part of the C language.  Is it
> possible to specify that this is an unsigned enum somehow?
> I've tried "enum symbol_redirect redirect : 3;" but at least GCC didn't
> like it.

Planned for C++0x:
http://en.wikipedia.org/wiki/C%2B%2B0x#Strongly_typed_enumerations

> Of course we can add one more bit (we have plenty of bits left there),
> but I'd first like to know how this is usually handled, since it seems
> to imply that MSVC always requires one extra bit to store enums.

Good old "unsigned redirect : 3;" works as expected.

Btw, check also "enum Lisp_Type type : GCTYPEBITS;".

--- grischka

>         Stefan