[PATCH] assert: Suppress pedantic warning caused by statement expression [BZ# 21242]

[Florian Weimer]

On 07/04/2017 04:00 PM, Florian Weimer wrote:
> On 06/26/2017 12:56 PM, Joseph Myers wrote:
>> On Sun, 25 Jun 2017, Florian Weimer wrote:
>>
>>> I think we can use __extension__ if we also expand the expression
>>> without __extension__ in an unevaluated context.  The tricky part is to
>>> find one that is independent of GNU extensions.
>>> Perhaps this would work?
>>>
>>> #  define assert(expr)                                           \
>>>   ((void) sizeof ((expr) == 0), __extension__ ({                 \
>>>       if (expr)                                                  \
>>>         ; /* empty */                                            \
>>>       else                                                       \
>>>         __assert_fail (#expr, __FILE__, __LINE__, __FUNCTION__); \
>>>     }))
>>>
>>> sizeof suppresses the evaluation of the first occurrence of expr.  The
>>> comparison is needed because sizeof cannot be applied to function
>>> pointers and bitfields.  C11 says that expr is compared to zero, so the
>>> (expr) == 0 expression is well-formed.
>>>
>>> What do you think?  Should we make this change?
>>
>> I think that's reasonable (appropriately commented to explain why it's 
>> done that way).
> 
> This is what I came up with as a patch.
> 
> I would consider this still appropriate during the freeze.  It's
> something we'd backport to glibc 2.25, too.

Hopefully now with attachment.

Florian

-------------- next part --------------
A non-text attachment was scrubbed...
Name: assert.patch
Type: text/x-patch
Size: 1616 bytes
Desc: not available
URL: <http://sourceware.org/pipermail/libc-alpha/attachments/20170704/c815c2bf/attachment.bin>