Using __STDC_VERSION__ macro

[Mason]

On 01/02/2017 14:52, Jonathan Wakely wrote:
> On 1 February 2017 at 13:49, Mason wrote:
>> Hello,
>>
>> https://gcc.gnu.org/gcc-5/porting_to.html states
>>
>> "Typically, this macro is used as in the following:
>>
>>   #if !defined __STDC_VERSION__ || __STDC_VERSION__ < 199901L
>>     /* ... */
>>   #else
>>   # include <stdint.h>
>>   #endif
>> "
>>
>> I think it is unnecessary to test for the existence of __STDC_VERSION__
>> because N1256 6.10.1p4 states
>> "all remaining identifiers [...] are replaced with the pp-number 0"
>>
>> Therefore
>> #if __STDC_VERSION__ < 199901L
>> would work as expected, even when __STDC_VERSION__ is undefined.
>> (As the constant-expression would be false.)
> 
> But you'd get a warning with -Wundef

Right.

I'm not convinced by the usefulness of -Wundef, though.

I suppose its only use is catching typos such as

#define FOO 42
#if GOO
#endif

which would silently discard the conditional code.

Regards.