How to globally #define a preprocessor variable?

问题

I'm programming an Arduino sketch in C++. I want the user to be able to #definea constant directly in the sketch.ino file which will be needed to compile the code. The Arduino IDE uses a g++ compiler.

Let's assume we have three files:

sketch.ino
sketch.h
sketch.cpp

In sketch.h I defined

#define OPTION_1 0
#define OPTION_2 1
#define OPTION_3 2
#define OPTION_4 3
#define SLOW 0
#define FAST 1

In sketch.ino the user then defines MYOPTION:

#define MYOPTION OPTION_2

In sketch.h I use the variable to define macros:

#if MYOPTION == OPTION_1 | MYOPTION == OPTION_2
    #define SPEED FAST
#else
    #define SPEED SLOW
#endif

In sketch.cpp I use it to improve time critical code:

MyClass::foo() {
    // do something
    #if SPEED == FAST
    // do more
    #if MYOPTION == OPTION_2
    // do something extra
    #endif
    #endif
    #if MYOPTION == OPTION_4
    // do something else
    #endif
    }

Unfortunately the definition of MYOPTION doesn't seem to be recognized inside sketch.cpp. Hower sketch.cpp does recognize variables defined in sketch.h. Is there a way to define preprocessor variables globally, so they can be accessed in any file that uses them?

回答1:

Move the option definitions to a separate file, e.g. options.h. You could also define them in sketch.ino if you like.
Include options.h in sketch.ino and sketch.h.
Move all the code that relies on the MYOPTION macro from sketch.cpp to sketch.h.
Define MYOPTION in sketch.ino before including sketch.h:

#include "options.h"
#define MYOPTION OPTION_2
#include "sketch.h"

Here's an example of a popular library that uses this technique:

https://github.com/PaulStoffregen/Encoder

It allows the user to configure the use of interrupts from the sketch via the ENCODER_DO_NOT_USE_INTERRUPTS and ENCODER_OPTIMIZE_INTERRUPTS macros.

来源：https://stackoverflow.com/questions/45393975/how-to-globally-define-a-preprocessor-variable

标签

c++

arduino

g++

global

preprocessor