Re: [Toon-members] TooN Matrix--->Access to the data structure?

[E. Rosten]

On Mon, 28 Sep 2009, "Gabriel Nützi" wrote:

> Hello
>
> I really need quick help
>
> How can I get the data pointer of a TooN Matrix or Vector like:
> Matrix<> A(3,1)
>
> I need a pointer to the stored data because I want to copy this to matlab in 
> c++ by memcpy()...
>
> &A(0,0) works only for the first element, its dynamic.....
>
> Can anybody help me? Whats the correct Syntax?
>
> Thanks alot!

If you declare:

Matrix<> A(3, 1);

Then the data is contiguous and &A(0,0) will give you the pointer to the 
first element, so you can to use memcpy. However, if your matrix is 
ColMajor, then you might not get the right answer.

However, if you use slices, the data is not contiguous, so:

Matrix<> A(3, 3);

&A.slice(2,2)(0,0) //You don't want to memcpy this pointer!


The best solution is to write a function which does a double 
for-loop over the matrix and copies the data. This will work slices, 
ColMajor, RowMajor and so on. Something like:

template<int R, int C, class P, class B>
void matrix_copy(const Matrix<R, C, P, B>& in, P* out)
{
   for(int r=0; r < in.num_rows(); r++)
    for(int c=0; c < in.num_cols(); c++)
     *out++ = in[r][c];
}

Swap the order of the loops if matlab stores things as column major.

-Ed


--
(You can't go wrong with psycho-rats.)(http://mi.eng.cam.ac.uk/~er258)

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