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I am trying to create a library, where I have an array of pointers to functions in it. This array is used by other functions in the library. This is the code of the header file:

class Lib {
  public:
    static void call();
    static void (*caller[])();
  private:
};

This is the code of the .cpp-file:

#include "Lib.h"

void (*caller[2])();

void Lib::call() {
  caller[0]();
}

The sketch executing this is

#include <Lib.h>

void setup() {
  Lib::call();
}

void loop() {}

When I try to compile this, I get the following error:

undefined reference to `Lib::caller'
collect2: error: ld returned 1 exit status
Mehrere Bibliotheken wurden für "Lib.h" gefunden

Another weird thing is that the error about the multiple found libraries goes away if I take away the line

Lib::call();

However, if I put the same code directly into the sketch like so:

void (*caller[2])();

void call() {
  caller[0]();
}

void setup() {
  call();
}

void loop() {}

I get no error. What's the problem here?

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void (*caller[2])();

should be:

void (*Lib::caller[2])();

Since you are defining storage space for a static member variable you have to tell the compiler what class it's a static member of.

  • Thanks, that solves the part about the undefined reference. How does the problem with the multiple libraries originate from this though? – LukasFun Oct 30 at 12:00
  • Probably because you do have two libraries named Lib.h somewhere? – Majenko Oct 30 at 12:06
  • (incidentally, I don't speak german, so had no clue what you were on about at first about multiple libraries...) – Majenko Oct 30 at 12:09
  • No, there is just one Lib.h file. The funny thing is, that, as I wrote, this error goes away when not calling the function in the sketch. And it also goes away with your solution. I was just wondering where it originated from. – LukasFun Oct 30 at 12:49
  • Probably some bug in the IDE then... – Majenko Oct 30 at 13:14

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