Re: [avr-gcc-list] Can enumerator values be used in a #if preprocessordirective?

[David Brown]

On 30/08/2011 14:03, Bob Paddock wrote:
> > > Refinements of the concept left as an exercise for the reader. Regards,
> >
> > Does that mean I am not allowed to post my refinements?
>
> No.  Please post.  Extra points for using __FILE__ __FUNCITON__ and
> __LINE__ to give meaningful error message.

The error message already contains information about the line number, 
just like for any other error message.

You can't get very meaningful errors here - I have not found any way to 
get a user-defined error message in conjunction with static asserts. 
There is, AFAIK, an effort to get standardised static assertions into 
both C and C++ with useful messages.  But in a fine example of 
mind-blowing stupidity, C++0x uses
        static_assert(expression, message)
while C1x calls it _Static_assert.

If your compiler supports static_assert or _Static_assert (gcc 4.6 
onwards) then you are best using it directly.

> Digging out my old issue of Embedded Systems on Compile Time Assertions
> we find this:
> http://www.eetimes.com/discussion/programming-pointers/4025549/Catching-errors-early-with-compile-time-assertions
>
> One thing to watch out for in some of the examples I've seen is in C99
> a zero length variable array could be created.

My macros (message is for compatibility with future C/C++ standards, and 
self-documentation of the code - it is not used by the macro):

#define STATIC_ASSERT_NAME_(line)       STATIC_ASSERT_NAME2_(line)
#define STATIC_ASSERT_NAME2_(line)      assertion_failed_at_line_##line

#define static_assert(claim, message) \
        typedef struct { \
                char STATIC_ASSERT_NAME_(__LINE__) [(claim) ? 1 : -1]; \
        } STATIC_ASSERT_NAME_(__LINE__)