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.

• Code Gorilla: I wouldn't use DEBUG if I was you, some compilers define it. You might want to look at printf which may solve you needs.
• Code Gorilla: Have you tried copying someone elses library and renaming the folders and files as appropriate. You might have an issue because the source file has no substance, so the compiler won't actually generate an object it can link against. You could stick a dummy function in there if this becomes an issue. In this case another solution would be to just define a header file and store it in a central location and do a 'include "..\DebugFile.h"` - dirty but effective.
• R Lloyd: yea i have been tossing up what exact command to call it. i want something simple and DEBUG() was working sofar but i might change it.. easy enough.. no substance yes good thinking ill keep it in mind. so you mean just a .h and not do much if anything with .cpp? because that would be oh so much less to think about
• user31481: You need to put your code inside bracket to make it a single statement. Otherwise, if (something) DEBUG3(x,y,z); will not give you what you want.

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 (<>).

• R Lloyd: thank you sir . this worked and solved the issue.. i was thinking it would be more complicated to do from all the content out there about libraries and not realzing what exactly a the #include and .h file actually do cheers

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";
}

• user31481: That's is an overly complicated solution for a OP that is struggling with using #define. OP approach does the thing in a simple and easily comprehensible way. I love you, Edgar, but C++ looks like the unwanted child of PHP raping JavaScript.
• R Lloyd: thanks both of you. Alterno i agree haha. i had a look at a few of the other ways to go about toggling serial debug lines @COMPILE TIME. all of which seem really long winded and overly complicated. {{{continue on next}}}
• R Lloyd: my approach seems to work a lot better than i had expected. being simple to implement a long chain of serial data and with ZERO change in overhead compared to Serial.print when DEBUG enabled(extra spaces aside..), and also ZERO overhead (as if all Serial.print was // commented out..) when disabled. it literally turns it all on or completely eliminates it. i discovered if i put all the #define DEBUG#(X) into an otherwise enpty sketch and #include <DIR\sketch.ino> that works its not a proper library but i guess it'l do if i cant make the library work