overloading [][] operators in c++

Question

I'm writing a matrix 3x3 class in c++.

glm::mat3 provides access to matrix data through the [][] operator syntax.
e.g. myMatrix[0][0] = 1.0f; would set the first row, first column entry to 1.0f.

I'd like to provide similar access. How can I overload the [][] operators?

I've tried the following, but I get errors:

operator name must be declared as a function

const real operator[][](int row, int col) const
{
    // should really throw an exception for out of bounds indices
    return ((row >= 0 && row <= 2) && (col >= 0 && col <= 2)) ? _data[row][col] : 0.0f;
}

What's the correct way to overload this operator?

Answer 1

There is no operator [][], so you need to overload the [] operator twice: once on the matrix, returning a surrogate object for the row, and once for the returned surrogate row:

// Matrix's operator[]
const row_proxy operator[](int row) const
{
    return row_proxy(this, row);
}
// Proxy's operator[]
const real operator[](int col) const
{
    // Proxy stores a pointer to matrix and the row passed into the first [] operator
    return ((this->row >= 0 && this->row <= 2) && (col >= 0 && col <= 2)) ? this->matrix->_data[this->row][col] : 0.0f;
}