Inherit an array that is initialised in the child

Question

I'm looking for the best way to do something like this:

class variable{
    protected:
    variable()
    int convert[][]
}

class weight: variable{
    public:
    weight(){
        convert = {{1,2},{1,3},{2,5}}
    }

Now I know I can't do this as I have to declare the array size in advance. I have many classes all inheriting from base class variable, and variable has a function using convert so don't want to declare convert in each one separately. For each class the array length will stay constant so using a list seems unnecessary. What are your suggestions.

Many thanks.

Answer 1

There are several options.

• Use std::vector.
• Or use std::array (available in C++11 only)

• Or do something like this:

  template<size_t M, size_t N>
  class variable{
     protected:
       int convert[M][N];
  };
  
  class weight: variable<3,2>{
  public:.
   weight(){
     //convert = {{1,2},{1,3},{2,5}} //you cannot do this for arrays
     //but you can do this:
     int temp[3][2] = {{1,2},{1,3},{2,5}};
     std::copy(&temp[0][0], &temp[0][0] + (3*2), &convert[0][0]);
  };
  

• Or you can use std::vector or std::array along with template as well.