Re: mutually referential (Pg 140 K&R2)

pete <pfiland@xxxxxxxxxxxxxx> writes:
> Dave Thompson wrote:
[...]
>> Forward declared struct and union tags are incomplete, until (the end
>> of) the full definition (if any). You can't forward declare an enum
>> tag; technically an enum type is incomplete from its type-specifier to
>> its closing brace, but this only means you can't use sizeof(enum foo)
>> as one of its own values which seems pretty silly anyway.
>
> I think you can. The enum type is complete,
> that is to say that it's type size is known at compile time,
> even if it's values haven't been specified.
>
> /* BEGIN new.c */
>
> #include <stdio.h>
>
> int main(void)
> {
> enum foo {Zero = sizeof (enum foo), One};
> enum bar;
>
> printf("sizeof (enum bar) is %lu bytes\n.",
> (long unsigned)sizeof(enum bar));
> return One - Zero - 1;
> }
>
> /* END new.c */

No. C99 6.7.2.2p4 says:

Each enumerated type shall be compatible with char, a signed
integer type, or an unsigned integer type. The choice of type is
implementation-defined, but shall be capable of representing
the values of all the members of the enumeration. The enumerated
type is incomplete until after the } that terminates the list of
enumerator declarations.

A footnote says:

An implementation may delay the choice of which integer type until
all enumeration constants have been seen.

If your compiler accepts the above code (in conforming mode), it's
probably broken. <OT>gcc doesn't.</OT>

--
Keith Thompson (The_Other_Keith) kst-u@xxxxxxx <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
.

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