How to create derive from templated class and overload constructor? C++

Question

I have templated class vector<typename T,size S> (I have to use this instead of std::vector ). I would like to specify an alias which is in type of vector<double,2> , but I also need to count the amount of all created and all currently live objects of this. Here's fragment of my templated class:

template<typename T, size S>
class vector{
  private:
    T *_values;
  public:
    vector():
      _values(new T[S]){
        for(int i =0; i < S; i++)
          _values[i] = T();
    }
    ~vector(){
      delete[] _values;
    }
};

So I thought about creating class named vector2D which inherits vector<double,2> and with two additional static variables to count its amounts. But how to do that? How to invoke superclass constructor and destructor so that it only contains incrementation/decrementation of these two static variables? vector2D is going to be used often in project I have to do. Maybe there is better solution?

PS How to pretty initialize *_values ? I tried *_values = { 0 } but it didn't work (of course assuming this is going to be a table of primitive types).

Answer 1

I would like to specify an alias which is in type of vector<double, 2>

Well that's simple:

typedef vector<double, 2> vector2D

but I also need to count the amount of all created and all currently live objects of this.

That's simple as well. Here's a small example:

#include <iostream>

template <typename T, int S>
class vec {

    public:

    vec() {
        ++obj_counter;
    }

    static int obj_counter;

};

template <typename T, int S>
int vec<T, S>::obj_counter = 0;

typedef vec<double, 2> vec2d;

int main() {

    vec<int, 1> intvec1;
    vec<int, 1> intvec12;
    vec2d doublevec2;

    std::cout << vec2d::obj_counter << std::endl;

    return 0;
}

The advantage of this is the fact that obj_counter works for every type. In the above example if you type:

std::cout << vec<int, 1>::obj_counter << std::endl;

It will print 2 .