How to overload a matrix class?

[featips]

Suppose I define a class called Matrix

template <class T>
class Matrix {
    ......
private:
    vector< vector<T> > data;
};

My question is: how to overload Matrix[i][j] which take two integers i and j as parameters?

This is an interview question that I was asked, and the interviewer precluded the way of using Matrix(i,j). Thanks a lot.

[Joeman]

i would have said overloading () is not the the same as overloading [] to achieve [][]

template< typename T >
class Matrix 
{
private:
    vector< vector<T> > data;
public:
    vector<T>&  operator[]( size_t Id ){ return data[Id]; }
};

As you can see this is simple. Nothing too complicated.

[featips]

The interviewer ask me to do the overloading so that I can use mtx[i][j] to access an element, where mtx is a Matrix object.

Obviously, you code can not do this.

[Paul McKenzie]

The interviewer ask me to do the overloading so that I can use mtx[i][j] to access an element, where mtx is a Matrix object.

Obviously, you code can not do this.

First, there is no such thing as overloading operator[][]. You can only overload operator[]. Your interviewer needs to clarify the question.

Second, the code does work.

#include <vector>

template< typename T >
class Matrix 
{
private:
    std::vector< std::vector<T> > data;
public:
    std::vector<T>&  operator[]( size_t Id ){ return data[Id]; }
};

int main()
{
   Matrix<int> mt;
   mt[0][0] = 10;
}

This compiles with no errors.

Regards,

Paul McKenzie

[nbaztec]

@featips,
The code posted by Joeman is correct as far as logic is concerned. It's entirely upto you how you want to go on with it.
In a 2-D array '[]' returns the element at that index (row or column). So subsequent calls to '[]' ends
up fetching the data itself. Notice that there are no separate overloads for '[]' for 1D, 2D, 3D, etc. arrays.
Similarly the operator '[]' in case of your class can be made to return a row/column/1-D array too which with subsequent calls will finally fetch you the data.

Regards,
Nisheeth Barthwal