Question

I am trying to access this C++ function from the C# code in my program

Tridiagonal3 (float** mat, float* diag, float* subd)
{
   float a = mat[0][0], b = mat[0][1], c = mat[0][2],
                        d = mat[1][1], e = mat[1][2],
                                       f = mat[2][2];

}

The call is as shown below

tred2(tensor, eigenValues, eigenVectors);

where tensor is float[,] and eigenvalues and eigenvectors are float[] arrays.

When i try doing this i get an exception

Access violation reading location 0x3f5dce99

when i try accessing

float a = mat[0][0]

What could be happening?

Answer 1

Tridiagonal3 (float** mat, float* diag, float* subd)

mat is a double-pointer type (pointer to pointer).
In C#, float[,] is not a double-pointer. It’s just syntactic sugar for accessing a multi-dimensional array, just like you would do mat[x + y * width] instead of mat[y][x];

In other words, you are passing a float* to your C++ application, not a float**.

You should change the way you use mat to access elements using the manual offset, like mat[y + 2 * x]