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

[Victor Aprea]

No the original suggestion of (&LED1_DDR == &LED2_DDR) is necessary because of the way the DDRs are defined (they are the value of register)... the ampersands get you back to the register address, which is more likely what you are trying to determine with such a statement.

Vic

On Sun, Jun 3, 2012 at 3:29 PM, Joerg Wunsch <address@hidden> wrote:

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) {
   // ...
 } else {
   // both DDRs are not the same
   // ...
 }

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