Error compiling codes: undefined reference

Using Arduino Programming Questions
1 
AppData\Local\Temp\ccsbCXFP.ltrans0.ltrans.o: In function `global constructors keyed to 65535_0_ArrayList.cpp.o.2153':
<artificial>:(.text.startup+0x46): undefined reference to `ArrayList<int>::ArrayList(int)'
<artificial>:(.text.startup+0x50): undefined reference to `ArrayList<int>::ArrayList(int)'
<artificial>:(.text.startup+0x60): undefined reference to `Device<float>::Device(ArrayList<int>)'
collect2.exe: error: ld returned 1 exit status

exit status 1

Compilation error: exit status 1

ArrayList.h

template<typename E>
class ArrayList {
private:
    int _size;
    E *const _array = {};
    void grow(int minCapacity);
    void ensureExplicitCapacity(int minCapacity);
    void ensureCapacityInternal(int minCapacity);

public:
    ArrayList();
    ArrayList(int initialCapacity);
    ArrayList(E *const initialArray);

ArrayList.cpp

template<typename E>
ArrayList<E>::ArrayList(int initialCapacity) {
    _array = new E[initialCapacity];
}
template<typename E>
ArrayList<E>::ArrayList(E *const initialArray) {
    _array = initialArray;
}
2

your class definition is missing the trailing }; and the .cpp would need to #include "ArrayList.h"

you also have to think it terms of who owns the array and add a destructor. May be something like this

.h

#ifndef __ARRAYLIST___
#define __ARRAYLIST___
#include <Arduino.h>

template<typename E>
class ArrayList {
private:
    int _size;
    E* _array;  // Removed const here as you want to change it
    void grow(size_t minCapacity);
    void ensureExplicitCapacity(size_t minCapacity);
    void ensureCapacityInternal(size_t minCapacity);

public:
    ArrayList(size_t initialCapacity = 10);
    ArrayList(E* const initialArray);
    ~ArrayList();  // Add a destructor to release allocated memory
};

#endif

.cpp

#include "ArrayList.h"

template<typename E>
ArrayList<E>::ArrayList(size_t initialCapacity) : _size(0), _array(new E[initialCapacity]) {}

template<typename E>
ArrayList<E>::ArrayList(E* const initialArray) : _size(0), _array(initialArray) {}

template<typename E>
void ArrayList<E>::grow(size_t minCapacity) {
    // Implement the grow function
}

template<typename E>
void ArrayList<E>::ensureExplicitCapacity(size_t minCapacity) {
    // Implement the ensureExplicitCapacity function
}

template<typename E>
void ArrayList<E>::ensureCapacityInternal(size_t minCapacity) {
    // Implement the ensureCapacityInternal function
}

template<typename E>
ArrayList<E>::~ArrayList() {
    delete[] _array;  // Release the allocated memory in the destructor
}

you'll have to explore exactly what it is you want from the constructor using an array
see also The rule of three/five/zero ➜ make the right decisions there, might need

    ArrayList(size_t initialCapacity = 10);
    ArrayList(const ArrayList& other);
    ArrayList(ArrayList&& other) noexcept;
    ArrayList& operator=(const ArrayList& other);
    ArrayList& operator=(ArrayList&& other) noexcept;
    ~ArrayList();
3

Thanks. I've encountered another similar problem.

/var/folders/x7/p119gjkx60n54k0hjx6p26br0000gn/T//ccPsrUEV.ltrans0.ltrans.o: In function `global constructors keyed to 65535_0_ArrayList.cpp.o.1815':
<artificial>:(.text.startup+0x60): undefined reference to `Device<float>::Device(int*)'

Device.h

#ifndef DEVICE_H
#define DEVICE_H


#include "Arduino.h"
#include "ArrayList.h"

template<typename T>
class Device {
protected:
    String _tag = "";
    ArrayList<String> _parentTags = new ArrayList<String>();
    int *const _pins;

public:
    Device(int *const pins);
    ~Device();
    void tag(String tag);
    String tag();
    void parentTags(ArrayList<String> parentTags);
    ArrayList<String> parentTags();
    void pinsCheck(int requiredNum);
    void initialize(String *parentTags);
    T read();
    void write(T payload);
    void close();
};
bool pulse(int pin);


#endif // DEVICE_H

Device.cpp

#include "Device.h"

template<typename T>
Device<T>::Device(int *const pins) : _pins(pins) {}
template<typename T>
Device<T>::~Device<T>() {
    delete[] _pins;
}
template<typename T>
void Device<T>::tag(String tag) {
    _tag = tag;
}
template<typename T>
String Device<T>::tag() {
    return _tag;
}
template<typename T>
void Device<T>::parentTags(ArrayList<String> parentTags) {
    _parentTags = parentTags;
}
template<typename T>
ArrayList<String> Device<T>::parentTags() {
    return _parentTags;
}
template<typename T>
void Device<T>::pinsCheck(int requiredNum) {
    if (sizeof(_pins) != requiredNum)
        throw value_error(format("This device only takes in {} pins", requiredNum));
}
bool pulse(int pin) { return digitalRead(pin) == LOW; }

WheelSpeedSensor.h

#ifndef WHEELSPEEDSENSOR_H
#define WHEELSPEEDSENSOR_H

#include "Device.h"

#define BOUNCETIME 20

class WheelSpeedSensor : public Device<float> {
protected:
    long _t1, _t2;

public:
    WheelSpeedSensor(int *const pins);
    void initialize();
    float read();
};


#endif // WHEELSPEEDSENSOR_H

WheelSpeedSensor.cpp

#include "WheelSpeedSensor.h"

WheelSpeedSensor::WheelSpeedSensor(int *const pins) : Device<float>(pins) {
}

void WheelSpeedSensor::initialize() { pinMode(_pins[0], INPUT); }

float WheelSpeedSensor::read() {
    if (millis() - _t2 > BOUNCETIME && pulse(_pins[0])) {
        _t1 = _t2;
        _t2 = millis();
    }
    return 60 / (_t2 - _t1);
}
4

All the template functions have to be in the .h file or they aren't seen from other compilation units.

5

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