Re: [Qemu-devel] [PATCH v3 2/4] compiler: rework BUG_ON using a struct

[Eric Blake]

On 01/20/2017 03:41 AM, Dr. David Alan Gilbert wrote:

>> -#define QEMU_BUILD_BUG_ON(x) \
>> -    typedef char glue(qemu_build_bug_on__, __LINE__)[(x) ? -1 : 1] \
>> -        __attribute__((unused))
>> +#define QEMU_BUILD_BUG_ON_STRUCT(x) \
>> +    struct { \
>> +        int qemu_build_bug_on : (x) ? -1 : 1; \
>> +    }
> 
> The problem with this is it can't be used as an expression, where as
> your previous version could.
> I've got a similar case (see previous reply) that needed an expression
> bug-on that would evaluate to zero.

Keep reading the series - the version usable in an expression is
QEMU_BUILD_BUG_ON_ZERO, introduced in 3/4.  Patch 2/4 is just rewriting
the existing check, with no change in the fact that it is still a
declaration.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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