Activating a defined macro in a class from main.cpp

Question

Sorry if this question been asked. I'm trying to activate certain function in a class using a macro defined in the class from main.cpp. I'm using jrowberg MPU6050 library if that matters.

main.cpp

#include "gyro.h"
gyro gyro(Serial);
#define OUTPUT_READABLE_EULER

void setup(){
...
}
void loop(){
...
}

gyro.cpp

  #include "gyro.h"
  #ifdef OUTPUT_READABLE_EULER
      // display Euler angles in degrees
      mpu.dmpGetQuaternion(&q, fifoBuffer);
      mpu.dmpGetEuler(euler, &q);
      serial_.print("euler\t");
      serial_.print(euler[0] * 180/M_PI);
      serial_.print("\t");
      serial_.print(euler[1] * 180/M_PI);
      serial_.print("\t");
      serial_.println(euler[2] * 180/M_PI);
  #endif

If I define OUTPUT_READABLE_EULER in gyro.h, it works. But I want to do it from main.cpp.

Answer 1

You cannot not, but also you should not try to define a macro in a cpp file and use it in another cpp file.

Instead, you have to define it in a h (header) file, which is included in both cpp files.

Why would you define it in main.cpp or main.h anyway if you don't use it in those files?

You have mainly three options:

• Define it in gyro.h so you include it in gyro.cpp where you use it. You can later use it in other files as well.
• Define it in gyro.cpp so you can use it only in that file. This prevents the macro being used in other files (which can be safer).
• Define it in a separate file, e.g. euler.h and include this header file everywhere you need it.

See also Juraj's comments below.