Thread: Pointers and multi dimensional arrays

Hi,
I have troubles understanding the relationship between pointers (to double) and multidimensional arrays (of doubles).

I have a C++ routine that returns pointers to doubles, and a class object that I'm creating computes multidimensional arrays, because I like to think of the data as matrices.

Then when the computation is done all I have to do is to copy the array values into the location pointed by the pointer, increment it and so on.

So this is what I have:

Code:

void STDCALL FIESUB ( double *dfddis, double *dfdvel )
{
...
}

In this routine I instantiate an object of the class Field:

Code:

    class msField
    {
    private:
        double m_dfdx[6][6];
        double m_dfdxdot[6][6];
    public:
        void getForceDerivatives(double *fddist, double *fdvel);
    };

The idea being that in getForceDerivatives I would do something like this:

Code:

void msField::getForceDerivatives(double *fddist, double *fdvel)
{
    // retrieves the force derivatives from the field member datas
    int i, j;
    for ( i = 0; i < 6; i++)
    {
        for ( j = 0; j < 6; j++)
        {
            *fddist++=m_dfdx[i][j];
            *fdvel++=m_dfdxdot[i][j];
        }
    }
}

That function is called like this (inside of FIESUB):

Code:

rField.getForceDerivatives(dfddis, dfdvel);

The result?
Mayhem.
Obviously I am forgetting something.
Can anyone explain the relationship between pointers to double and arrays of doubles (multidimensional arrays, that is...).
Any help much appreciated!!
And72.