Return Array from Class

Question

I need to return 3 values. X, Y, Z. I've tried something like this, but it does not work, can anyone help me a bit? I've looked here: Return a float array in C++ and I tried to do same thing, except with 1 dimensional array to return.

class Calculate
{
 float myArray[3][4], originalArray[3][4], tempNumbers[4];
 float result[3]; // Only works when result is 2 dimensional array, but I need 1 dimension.

public:
 Calculate(float x1, float y1, float z1, float r1,
  float x2, float y2, float z2, float r2,
  float x3, float y3, float z3, float r3)
 {
  myArray[0][0] = x1;
  myArray[0][1] = y1;
  myArray[0][2] = z1;
  myArray[0][3] = r1;

  myArray[1][0] = x2;
  myArray[1][1] = y2;
  myArray[1][2] = z2;
  myArray[1][3] = r2;

  myArray[2][0] = x3;
  myArray[2][1] = y3;
  myArray[2][2] = z3;
  myArray[2][3] = r3;

  result[0] = 1;
  result[1] = 2;
  result[2] = 3;
 }

 float* operator[](int i)
 {
  return result[i]; //Value type does not match the function type
 }

 const float* operator[](int i) const
 {
  return result[i]; //Value type does not match the function type
 }
};

Answer 1

Instead of returning a pointer, it's usually better practice to accept a pointer and write out the results there. That way someone can allocate a regular array on the stack and have it initialized by your Calculate.

Something like:

class Calculate
{
 float myArray[3][4], originalArray[3][4], tempNumbers[4];

public:
 Calculate(float x1, float y1, float z1, float r1,
  float x2, float y2, float z2, float r2,
  float x3, float y3, float z3, float r3, float *result)
 {
  myArray[0][0] = x1;
  myArray[0][1] = y1;
  myArray[0][2] = z1;
  myArray[0][3] = r1;

  myArray[1][0] = x2;
  myArray[1][1] = y2;
  myArray[1][2] = z2;
  myArray[1][3] = r2;

  myArray[2][0] = x3;
  myArray[2][1] = y3;
  myArray[2][2] = z3;
  myArray[2][3] = r3;

  result[0] = 1;
  result[1] = 2;
  result[2] = 3;
 }
};

Some other tweaks you can do - separate the constructor from the calculation, since constructors are more for initialization; and pass arrays for safer memory control:

class Calculate
{
    float myArray[3][4], originalArray[3][4], tempNumbers[4];

public:
    Calculate(const float initArray[3][4])
    {
        for (int i = 0; i < 3; i++)
            for (int j = 0; j < 4; j++)
                myArray[i][j] = initArray[i][j];
    }

    void DoCalculation(float result[3]) const
    {
        result[0] = 1;
        result[1] = 2;
        result[2] = 3;
    }
};

int main()
{
    float myArray[3][4] =
    {
        { 0, 1, 2, 3 },
        { 4, 5, 6, 7 },
        { 8, 9, 0, 1 }
    };
    float result[3];
    Calculate calc(myArray);
    calc.DoCalculation(result);
    return 0;
}