file.cpp

class Encoder {
    ...

    int32_t *_currentPosition;

    ...
}

Encoder::Encoder(int32_t *currentPosition, uint8_t ENCA, uint8_t ENCB) {
    _ENCA = ENCA;
    _ENCB = ENCB;
    _currentPosition = currentPosition;
    pinMode(_ENCA, INPUT_PULLUP);
    pinMode(_ENCB, INPUT_PULLUP);
    attachInterrupt(digitalPinToInterrupt(_ENCA), updateEncoder, RISING);
}

void Encoder::updateEncoder() {
    if (digitalRead(_ENCB) > 0) {
        *_currentPosition++;
    } else {
        *_currentPosition--;
    }
}