How to define a constant in a main and use it in other header files?

Question

file0: Main.ino (it's arduino file):

#define AXIS_SERIAL Serial1
#include "header.h"
...
void setup(){...}
void loop() {...}
...

file1: header.h

...
#ifndef AXIS_SERIAL
#define AXIS_SERIAL Serial
#endif
...

file2: header.cpp

...
AXIS_SERIAL.print("Hello World")
...

Question: When I use function in header.cpp value inside of AXIS_SERIAL is still Serial (not Serial1). Is there a way to define a constant in main file, and use it in other header file(s)? If so, it will going to generalize my piece of code.

I do know that it's possible to declare a variable something like HardwareSerial Axis_serial = Serial1; but I may use Software Serial in the future. So I need a thing that works both Hardware & Software Serial classes.

Have you looked at: https://stackoverflow.com/questions/10422034/when-to-use-extern-in-c ? — Programming Rage, Jan 04 '21 at 06:19
the header.cpp is a separate translation unit in which the define you have in ino isn't applied. https://forum.arduino.cc/index.php?topic=721040.msg4847132#msg4847132 — Juraj, Jan 04 '21 at 10:43

score -1 · Answer 1 · answered Jan 04 '21 at 07:50

-1

Yes, that should be possible, in the end the #define directive replaces your new "alias" with the string that you entered:

#define MY_DEFINE Serial

your code

void loop(){
   MY_DEFINE.println("Hello World!");
}

what your compiler sees:

void loop(){
   Serial.println("Hello World!");
}

answered Jan 04 '21 at 07:50

Max Kofler

86
4

Yes, In main.ino file, AXIS_SERIAL is Serial1. However, when I use functions declared in header.cpp (which uses AXIS_SERIAL) AXIS_SERIAL is still Serial (not Serial1). – Garid Jan 04 '21 at 08:43
this is a wrong answer – Juraj Jan 04 '21 at 10:42

How to define a constant in a main and use it in other header files?

1 Answers1