sizeof?

sgt_bear:
Its not a must, i just want that my library knows how many values there are in a array. If i pass the lenght, thats also fine. But currently that doesnt work too..

you cannot create an array of length zero and simply add elements as you are trying to do:

private:
 uint16_t convFactor;
 uint16_t deadTime;
 uint32_t pulseCount[];
 uint32_t timeInterval[];
 uint32_t lastConversion[];

when you try to do this:

lastConversion[i] = 0;

all you are doing is stomping on memory you don't own!

use the template method I showed you to pass the array length... but you need to have a variable that holds that number.

template<uint8_t N>
class MyClass {
  private:
    uint32_t* myArray;
    size_t arrayLength;
  public:
    MyClass() {
      arrayLength = N;
      myArray = new uint32_t[arrayLength];
    }
    size_t getArrayLength (void) {
      return arrayLength;
    }
};

MyClass<10> myInstance;

void setup() {
  Serial.begin(9600);
  Serial.println(myInstance.getArrayLength());
}

void loop() {
  // put your main code here, to run repeatedly:

}