Error when using #if or #ifdef

Projects Programming
1

Dear all,

I try to make a sketch in which you can use a variety of display's to do the same task. I try to do this with a #define LCD_TYPE and place all the code between #if (LCD_TYPE == 1) and #endif for all the number of display's. At first this seemed to work just fine. I had #define LCD_TYPE 1 and designed the whole sketch for the first display at hand. Then I tried to move to the second LCD type and canged to #define LCD_TYPE 2 and made code in blocks with #if (LCD_TYPE == 2) #endif. But then I got weird error messages.

speedometer.ino: In function 'void setup()':
speedometer.ino:88:14: error: 'displayInit' was not declared in this scope
speedometer.ino: In function 'void loop()':
speedometer.ino:117:16: error: 'checkInput' was not declared in this scope
speedometer.ino:118:42: error: 'calcSpeed' was not declared in this scope
speedometer.ino:119:21: error: 'displaySpeed' was not declared in this scope
speedometer.ino:141:16: error: 'displayBusy' was not declared in this scope
speedometer.ino:144:16: error: 'displayIdle' was not declared in this scope
speedometer.ino: In function 'bool checkInput()':
speedometer.ino:165:11: error: 'class Adafruit_7segment' has no member named 'setCursor'
'displayInit' was not declared in this scope

At first I thought I did something wrong with an #endif or something. But if I changed back to the firt LCD everything was fine again. So I started a new sketch:

#define TEST 1

#if (TEST == 1)
  byte varname = 1;
#endif

#if (TEST == 2) 
  byte varname = 3;
#endif

void setup() {
  
  delay(2000);
  Serial.begin(9600);
  Serial.println(varname);
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}

If I run this I get a 1 at the serial monitor as expected. But if I change it to #define TEST 2 I get a compile error!

deftest.ino:12:3: error: 'byte' does not name a type
deftest.ino: In function 'void setup()':
deftest.ino:17:13: error: 'delay' was not declared in this scope
deftest.ino:18:3: error: 'Serial' was not declared in this scope
deftest.ino:19:18: error: 'varname' was not declared in this scope
'byte' does not name a type

Huh?? Why? And the line number in the error is off by 4 (line 12 is blank, it's line 8 in the sketch).

So I thought, mayby I can't check the value. So I edited to use #ifdef

#define TEST_A
//#define TEST_B


#ifdef TEST_A
  byte varname = 1;
#endif

#ifdef TEST_B
  byte varname = 3;
#endif

void setup() {
  
  delay(2000);
  Serial.begin(9600);
  Serial.println(varname);
  // put your setup code here, to run once:

}

void loop() {
  // put your main code here, to run repeatedly:

}

And again, I get a 1 in serial monitor. But if I change to
//#define TEST_A
#define TEST_B

deftest.ino:14:3: error: 'byte' does not name a type
deftest.ino: In function 'void setup()':
deftest.ino:19:13: error: 'delay' was not declared in this scope
deftest.ino:20:3: error: 'Serial' was not declared in this scope
deftest.ino:21:18: error: 'varname' was not declared in this scope
'byte' does not name a type

Hello again error!

Does anyone why it fails? I think it should just leave out a part of the code and compile the rest.

2

septillion:
Does anyone why it fails? I think it should just leave out a part of the code and compile the rest.

Remove the brackets in the comparison:

#define TEST 1

#if TEST == 1
  byte varname = 1;
#endif

#if TEST == 2
  byte varname = 3;
#endif
3

Does anyone why it fails? I think it should just leave out a part of the code and compile the rest.

The IDE modifies your code when it creates a cpp file for the compiler to compile. Using #if, #ifdef, #endif, etc. confuses it as to WHERE to make the modifications.

Usually adding something like

byte me;

as the first line of the sketch solves the problem.

4

Modifying my code when making the cpp, that's indeed the idea. Adding byte me; indeed fixes the problem! :o But why? Why does it fix it and why get's the compiler confused?

5

Why does it fix it and why get's the compiler confused?

The compiler isn't confused. The IDE is. It doesn't understand postprocessor directives. It assumes that the # is going to be followed by the word include.

So, what happens is that the IDE adds the #include statement to include Arduino.h, where byte and things like that are defined, after the first non-# statement in the code. In your case, that happens to be in the middle of a #if/#endif block that does not get compiled.

Adding a non-# statement at the top of the code gives the IDE a different (and correct) insertion point.

6

Thnx Paul! Explains it :smiley: But I really hope they fix it in the future.