Return a float array in C++

Question

I currently have a 4x4 matrix class in C++ and I store each value as a float:

Matrix4d::Matrix4d(const float& m00, const float& m01, const float& m02, const float& m03,
                   const float& m10, const float& m11, const float& m12, const float& m13,
                   const float& m20, const float& m21, const float& m22, const float& m23,
                   const float& m30, const float& m31, const float& m32, const float& m33)
{
    _m00 = m00;
    _m01 = m01;
    _m02 = m02;
    _m03 = m03;
    _m10 = m10;
    _m11 = m11;
    _m12 = m12;
    _m13 = m13;
    _m20 = m20;
    _m21 = m21;
    _m22 = m22;
    _m23 = m23;
    _m30 = m30;
    _m31 = m31;
    _m32 = m32;
    _m33 = m33;
}

My question is, how can I return a float array of this data? I have no problem creating the array in the class for example:

float arrayToReturn[16] = { m00, m01, m02, m03, ... m33 };

However I can not return this value from the class. I've read about returning a pointer to the array, but have had no luck with it.

Answer 1

1. Don't pass floats by const reference, pass them by value.

2. I assume you want to return the array so you can do indexing? Then don't return an array from you matrix class. Instead, overload the [] operator or something.

3. Also, I wouldn't use 16 member variables but one array instead. Makes indexing a lot easier.

Here is how I would probably do it:

class Matrix4d
{
    float matrix[4][4];

public:

    Matrix4d(float m00, float m01, float m02, float m03,
             float m10, float m11, float m12, float m13,
             float m20, float m21, float m22, float m23,
             float m30, float m31, float m32, float m33)
    {
        matrix[0][0] = m00;
        matrix[0][1] = m01;
        matrix[0][2] = m02;
        matrix[0][3] = m03;
        matrix[1][0] = m10;
        matrix[1][1] = m11;
        matrix[1][2] = m12;
        matrix[1][3] = m13;
        matrix[2][0] = m20;
        matrix[2][1] = m21;
        matrix[2][2] = m22;
        matrix[2][3] = m23;
        matrix[3][0] = m30;
        matrix[3][1] = m31;
        matrix[3][2] = m32;
        matrix[3][3] = m33;
    }

    float* operator[](int i)
    {
        return matrix[i];
    }

    const float* operator[](int i) const
    {
        return matrix[i];
    }
};

int main()
{
    Matrix4d test(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 17, 16);
    test[3][2] = 15;
}