How to use #define in a library I'm trying to write?

Question

I have written simple code to enable toggling of serial.print debug data.

  #define DEBUG
  #ifdef  DEBUG
    #define DEBUG3(x,y,z) Serial.print(x);Serial.print(" ");Serial.print(y);
     Serial.print(" "); Serial.println (z)
    #define DEBUG2(y,z) Serial.print(y);Serial.print(" ");Serial.println 
     (z)
    #define DEBUG(z) Serial.println(z)
    #define DEBUGln  Serial.println("");
  #else
    #define DEBUG3(x,y,z)
    #define DEBUG2(x,y)
    #define DEBUG(x)
    #define DEBUGln
  #endif

Then I can just call DEBUG3("words",value,"words"); anywhere in the sketch and it will automatically print out the text, int, strings, etc with a single space between and automatically go to next line etc etc.

Just define the correct number of fields to print and separate using commas.

If I want to turn off debug then I just comment out #define DEBUG at the top.

Now the issue is I don't want to copy in this code every time I want to use it, so it makes sense to make it a library so that I can just call something like:

#include <SERIAL_DEBUG.h>
#define DEBUG     (or //#define DEBUG) //to enable or disable

The reason being that sometimes I might want to print up to 10 things on a single line (not very often but it could happen).

This is my first library attempt and I'm having a hard time finding any information on how I would go about setting up the .h and .cpp files for this type of #define DEBUG(x) Serial.println(x) and the #define DEBUG (from sketch) parts.

Answer 1

Anything in a header file that is included with #include is literally pasted into the file at the point of the #include.

So anything in your sketch you want to place into a header file you can just place it in a header file and include that file at the same location where the original code was.

So you can have a header file debug.h:

  #ifdef  DEBUG
    #define DEBUG3(x,y,z) Serial.print(x);Serial.print(" ");Serial.print(y);
     Serial.print(" "); Serial.println (z)
    #define DEBUG2(y,z) Serial.print(y);Serial.print(" ");Serial.println 
     (z)
    #define DEBUG(z) Serial.println(z)
    #define DEBUGln  Serial.println("");
  #else
    #define DEBUG3(x,y,z)
    #define DEBUG2(x,y)
    #define DEBUG(x)
    #define DEBUGln
  #endif

And include that in your sketch at the right location:

#define DEBUG
#include "debug.h"

Note that the #define DEBUG must come before the #include. Remember: the #include is replaced by the content of the included file, so after preprocessing you end up with exactly what you had before in your sketch:

  #define DEBUG
  #ifdef  DEBUG
    #define DEBUG3(x,y,z) Serial.print(x);Serial.print(" ");Serial.print(y);
     Serial.print(" "); Serial.println (z)
    #define DEBUG2(y,z) Serial.print(y);Serial.print(" ");Serial.println 
     (z)
    #define DEBUG(z) Serial.println(z)
    #define DEBUGln  Serial.println("");
  #else
    #define DEBUG3(x,y,z)
    #define DEBUG2(x,y)
    #define DEBUG(x)
    #define DEBUGln
  #endif

The file can be in the same location as the sketch (in which case you should use #include "debug.h" or in a library folder (Arduino/libraries/debug/debug.h) in which case you should include it with #include <debug.h>. In the Arduino IDE it actually makes little or no difference which type of #include you use, but it does serve as a visual reminder that this is either a header included with the sketch ("") or an external library or system header (<>).

Answer 2

Not a direct answer to your question, but I would suggest a different approach based on streaming output, as described in the Arduino Playground: Adding Streaming (insertion-style) Output. In a nutshell, you define the << operator for Serial (and any other object that inherits from Print) in a way that allows you to write things like:

Serial << "My name is " << name << " and I am " << age << " years old.";

Now you can define a Debug object which would be, depending on whether you want debugging output or not:

• an alias to Serial
• a dummy object that just discards its input.

Example:

#define DEBUG_ON

// From https://playground.arduino.cc/Main/StreamingOutput
template<class T> inline Print& operator<<(Print &obj, T arg)
{ obj.print(arg); return obj; }

#ifdef DEBUG_ON
# define Debug Serial
#else
class DummyStream {
public:
    template<class T> DummyStream& operator<<(T arg)
    { (void) arg; return *this; }
} Debug;
#endif

void setup()
{
    const unsigned long BAUDRATE = 9600;
    Serial.begin(BAUDRATE);
    Debug << "Serial port open at " << BAUDRATE << " bps\r\n";
}