Re: Forward declaration of enum iterator_selection?

From: Ramsay Jones <ramsay@ramsayjones.plus.com>
Date: Aug 8, 2016, 18:52 UTC
Message-ID: <53ab8626-f862-a732-b369-abeab69a468f@ramsayjones.plus.com>
In-Reply-To: <c1ef8a65-844f-b676-cae0-abba87930063@ramsayjones.plus.com>

On 08/08/16 19:28, Ramsay Jones wrote:

Show 28 quoted lines

> 
> 
> On 08/08/16 17:30, Johannes Sixt wrote:
>> Am 07.08.2016 um 22:34 schrieb Ramsay Jones:
>>> On 05/08/16 23:26, Johannes Sixt wrote:
> [snip]
>>> At this point 'enum iterator_selection' is an incomplete type and may
>>> be used when the size of the object is not required. It is not needed,
>>> for example, when a typedef name is being declared as a pointer to, or
>>> as a function returning such a type. However, such a type must be
>>> complete before such a function is called or defined.
>>
>> All you say is true when it is a struct type, of course. But I doubt that there exists such a thing called "incomplete enumeration type" in C. In fact, with these keywords I found https://gcc.gnu.org/onlinedocs/gcc/Incomplete-Enums.html which indicates that this is a GCC extension.
> 
> Ah, well spotted!
> 
> You prompted me to look at the C99 (and C11) standards, in particular
> sections 6.7.2.2 (Enumeration specifiers) and 6.7.2.3 (Tags).
> 
> So, while (technically) enumeration types are incomplete prior to the
> closing } in its definition, the constraint imposed in 6.7.2.3-2 states:
> 
> 	"A type specifier of the form
> 		enum identifier
> 	without an enumerator list shall only appear after
> 	the type it specifies is complete"
> 
> which pretty much rules out its use here.

BTW, you can make gcc be that 'pickier compiler' you mentioned, thus:

$ rm refs.o
$ make CFLAGS='-g -O2 -Wall -std=c99 -pedantic' refs.o
    * new build flags
    CC refs.o
In file included from refs.c:8:0:
refs/refs-internal.h:363:14: warning: ISO C forbids forward references to ‘enum’ types [-Wpedantic]
 typedef enum iterator_selection ref_iterator_select_fn(
              ^
$

:-D

ATB, Ramsay Jones