Undefined reference to ... when passing a byte from a struct to pinMode

Projects Programming
1

Hi everyone.
I'm writing a code where I have a struct containing the pinmap of my device on a dedicated file. I then use this struct to initialize the pins and do other stuff. I import the object on another file with extern and try to set pinMode with that pin byte I saved inside this 'p_pinmap' object. This procedure for reasons I cannot understand make the compiler trow "undefined reference to 'p_pinmap' ". If I use digitalWrite or assign the member inside a new variable the complier doesn't complain.
Can somebody explain me what am I doing wrong?

//main.ino

#include "init.h"
#include "parameters.h"

extern const pins p_pinmap;

void setup() {
  //initiate the channels
  initialize();
}

void loop() {
  delay(1000);
}

//init.h

#ifndef _INIT_
#define _INIT_

void initialize();

#endif

//init.cpp

#include "init.h"
#include "parameters.h"

extern const pins p_pinmap;

void initialize(){
  pinMode(p_pinmap.LED_Clock,OUTPUT); //undefined reference
  pinMode(p_pinmap.Heater[1],OUTPUT); //undefined reference
  const byte a=5;                     //OK
  const byte b=p_pinmap.LED_Clock;    //OK
  pinMode(b,OUTPUT);                  //undefined reference
  pinMode(7,OUTPUT);                  //OK
  pinMode(a,OUTPUT);                  //OK
  
}

//parameters.h

#ifndef _PARAMETERS_
#define _PARAMETERS_

#include <Arduino.h>

/*-----PINOUT-----*/
struct pins {
  const byte Heater[4];
  const byte Temp[4];
  const byte AnPot[4];
  const byte LED_Clock;
  const byte LED_Data;
  const byte LED_Latch;
  const byte DHTPIN;
  pins():   //fill here the pin numbers from 1st channel to the last
    Heater({10,11,12,13}),
    Temp({2,3,4,5}),
    AnPot({A1,A2,A3,A4}),
    LED_Clock(6), LED_Data(7), LED_Latch(8), DHTPIN(9) {};
};

#endif

//parameters.cpp

#include "parameters.h"

const pins p_pinmap;
2

Put this in parameters.h after the struct declaration:

extern const pins p_pinmap;

Remove that line from you .ino file.

3

Const implies internal linkage, so you explicitly have to mark p_pinmap as extern in your .cpp file (e.g. by including the extern declaration in the header as gfvalvo suggested).

4

ok, this actually works but I don't really understand why it needs to be in the .h file if I don't use it there but I define it in the .cpp. .cpp is the compilation unit, isn't it?
This was a snippet that I shortened but the actual code that I wrote in the parameters.h contains another bigger struct that contains multiple variables used everywhere and as this p_pinmap I define it only in the .cpp and not in the .h. For that struct / object that I extern the compiler doesn't complain anywhere.

5

Well, actually I had the same problem with that other struct. Undefined reference. I had created only the .h file and implemented therr the definiton and declaration. Than I resolved the problem by creating the .cpp file of parameters and moving there the definition of the object. So I don't know why for this struct p_pinmap now it asks again tu put the extern definition back in the header file.

6

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