C++ multidimensional array operator

Question

it is possible to overload somehow operator for multidimensional array?

Something like:

class A {
  ...
  int& operator[][] (const int x, const i         


        

Answer 1

No, there's just operator[]. As an alternative, you can overload:

int &operator()(int x, int y);

You can use that:

m(4, 5);

Answer 2

You need to overload operator[] and make it return a new class which only has another operator[].

Answer 3

Nope, that is not possible. There are two alternatives, though:

You can have operator[] return an array of a smaller dimension (For a 3D array, it will return a 2D array, for a 2D array it will return a 1D array, and for a 1D array, it will return a single element). Then you can "string them together" with the syntax you want. (arr[x][y][z])

Alternatively, you can overload operator(), because that can take multiple arguments.

Then you can use it like this, to index into a 3D array for example: arr(x,y,z)

But you can't overload [][] or [][][] as a single operator.

Answer 4

Not directly, but you can achieve the same functionality overloading operator[]() and having it return something that supports operator[]() itself.

For example:

class A {
  std::vector<std::vector<int> > vec;
public:
  std::vector<int>& operator[] (int x)
  {
      return vec[x];
  }
};

would allow you to write:

A a;
//...
int y = a[1][2];

because a[1] returns a std::vector<int> to which you can apply operator[](2).

Answer 5

There's no operator like that. I implemented, some times ago, a matrix trying to be close to the stl standards. And I used this method: first I've overloaded the operator[] to return another class that I called _C_row:

_C_row operator[](size_type index) { return _C_row(/*some parameters*/); } ///< This operator is overloaded to permit the use of double pointer notation.
_C_row operator[](size_type index) const { return _C_row(/*some parameters*/); } ///< This operator is overloaded to permit the use of double pointer notation.

And in _C_row I overloaded more than the operator[]:

value_type operator*() { return _r[0]; }
pointer operator->() { return _i[_idx]; }
double_pointer operator&() { return &(_i[_idx]); }
reference operator[](size_type col) { return _r[col]; }
const_reference operator[](size_type col) const { return _r[col]; }

I found this solution is very flexible. I hope my answer could be useful for you.

Answer 6

As mentionned before, there is no such thing as operator[][]. However, here is an an implementation using nested classes similar to what "jalf" proposed. For sake of simplicity, I hardcoded a 3x3 raw array.

    class Array2D final{
    public:
        class PartialArr final{
    private:
        friend Array2D;
        PartialArr(Array2D* ptr, int index) :original(ptr), firstIndex(index) {}
        int firstIndex;
        Array2D* original;
    public:
        int& operator[](int index) { return this->original->data[firstIndex][index];  }
    };

        PartialArr operator[](int index) { return PartialArr(this, index); }
    private:
        int data[3][3];
    };

This solution prevents the user of Array2D to manipulate the data directly when indexing only the first dimension of the array.

const versions of both operator[] could also be added to make the class complete.