Question

Possible Duplicate:
Operator[][] overload

I have made class which contains an array containing (in one row) all the numbers from the given 2d array. For example given: {{1,2}{3,4}} the b field in the object of class T contains {1,2,3,4}. I would like to overload[][] operator for this class so it will work like that

T* t.....new etc.
int val = (*t)[i][j]; //I get t->b[i*j + j] b is an 1dimension array

---

    class T{
    public:
        int* b;
        int m, n;
        T(int** a, int m, int n){
            b = new int[m*n];
            this->m = m;
            this->n = n;
            int counter = 0;
            for(int i  = 0; i < m; i++){
                for(int j = 0; j < n; j++){
                    b[counter] = a[i][j];
                    counter++;
                }
            }
        }
int main()
{
    int m = 3, n = 5, c = 0;
    int** tab = new int*[m];
    for(int i = 0; i < m; i++)
           tab[i] = new int[n];
    for(int i  = 0; i < m; i++){
        for(int j = 0; j < n; j++){
            tab[i][j] = c;
            c++;
            cout<<tab[i][j]<<"\t";
        }
        cout<<"\n";
    }


    T* t = new T(tab,3,5);

    };

Answer 1

You cannot. You have to overload operator[] to return a proxy object, that in turn, overloads operator[] to return the final value.

Something like:

class TRow
{
public:
    TRow(T &t, int r)
    :m_t(t), m_r(r)
    {}
    int operator[](int c)
    {
        return m_t.tab[m_t.n*m_r + c];
    }
private:
    T &m_t;
    int m_r;
};

class T
{
    friend class TRow;
    /*...*/
public:
    TRow operator[](int r)
    {
         return TRow(*this, r);
    }
};

Instead of saving a T& in TRow you could save directly a pointer to the row, that’s up to you.

A nice feature of this solution is that you can use the TRow for other things such as operator int*().