Compiler problem? [SOLVED]

Projects Programming
1

I've run into a weird problem with (I presume) the compiler and managed to reduce it to a few small test cases. I have tested them on V.0023 and V1.0 and they all work/fail the same way - I have a Duemilanove 328.
I'll start with the code from the description of setup() at setup() - Arduino Reference
This compiles (as it should):

int buttonPin = 3;
void setup()
{
  Serial.begin(9600);
  pinMode(buttonPin, INPUT);
}
void loop()
{
  // ...
}

Now let's suppose that the use of the buttonPin is optional and modify it so that it can be removed with ifdef - this also compiles:

#define NO_BUTTON
#ifdef NO_BUTTON
int buttonPin = 3;
#endif
void setup()
{
  Serial.begin(9600);
#ifdef NO_BUTTON
  pinMode(buttonPin, INPUT);
#endif
}
void loop()
{
  // ...
}

BUT if I decide I don't want the button, commenting the define out like this:

//#define NO_BUTTON
#ifdef NO_BUTTON
int buttonPin = 3;
#endif
void setup()
{
  Serial.begin(9600);
#ifdef NO_BUTTON
  pinMode(buttonPin, INPUT);
#endif
}
void loop()
{
  // ...
}

gives the compiler error message:

test23.cpp: In function 'void setup()':
test23:6: error: 'Serial' was not declared in this scope

Why?

Pete
P.S. I searched for this message and couldn't find any solution.

2

It has to do with how the IDE adds include statements to the .cpp file that it creates from your sketch. Include files are added, if I remember correctly, before the first executable statement in the code. So, they get added in the middle of your #ifdef block. When that block is not active, neither are any of the include files. You need to add some dummy code before the commented out #define statement so the IDE can find the right insertion point for the include files.

3

When I add "char dummy;" in front of the define all is well!
Thanks very much Paul.
Pete