Re: [avr-gcc-list] Check whether two macros are equal to each other

[Georg-Johann Lay]

Joerg Wunsch schrieb:
> Georg-Johann Lay <address@hidden> wrote:
>
> > > Could anyone explain this to me? Is there any way around this
> > > (still using macros)?
>
> > With macros? No way here.
>
> Well: no way *at the preprocessor level*.
>
> However, moving the comparison to the *compiler level* could work.
> The values of e.g. DDRD and DDRB are expressions that can be compared
> by the compiler.  As the resulting comparison is constant at
> compile-time, with optimization enabled, those code portions that can
> never be reached (due to the compile-time constant comparisons) are
> optimized away.
>
> So, turn your
>
> #if LED1_DDR == LED2_DDR
>
> into
>
>   if (LED1_DDR == LED2_DDR) {

As I already wrote, the right C-level condition is

if (&LED1_DDR == &LED2_DDR)

You don't want to /read/ from the ports.

Johann