Re: [PATCH] stdnoreturn: new module

[Eric Blake]

On 02/28/2012 01:45 AM, Paul Eggert wrote:
> On 02/27/2012 06:29 PM, Bruno Haible wrote:
>> The current set of definitions
>>
>>   #define _Noreturn __declspec (noreturn)
>>   #define noreturn _Noreturn
>>
>> leads to a syntax error when someone writes  __declspec (noreturn),
>> because preprocessing transforms it to  __declspec (__declspec (noreturn)).
>>
>> How can this syntax error be avoided?
> 
> I don't see any reasonable way to do it.
> Perhaps we should just document that <stdnoreturn.h> is
> incompatible with MSVC, unless it is included after all
> system include files (yuck!).

This works:

$ cat foo.c
#define noreturn __declspec(noreturn)
#define _Noreturn noreturn
noreturn
_Noreturn
$ gcc -E foo.c | tail -n2
__declspec(noreturn)
__declspec(noreturn)

The trick is that on MSVC, we have to define noreturn in terms of
itself, so that pre-processing doesn't recursively expand things, then
_Noreturn is defined in terms of noreturn.

I think that if <config.h> expands _Noreturn to 'declspec(noreturn)',
but <stdnoreturn.h> undefined _Noreturn, defines noreturn, then
redefines _Noreturn, that you'll have a working solution - so you need
to add compiler conditionals to our <stdnoreturn.h> header to get this
ordering for MSVC.

-- 
Eric Blake   address@hidden    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

signature.asc
Description: OpenPGP digital signature