[Boost-users] [Boost][multi_array] copying a float array to a particular dimension of a multi_array

From: Sebastien Fortier (sebastien.fortier_at_[hidden])
Date: 2006-08-11 09:31:17

I would like to know if it is possible to use memcpy to copy a float 
array to a particular dimension of a multi_array.

ex.:
I declare a 3 dimension multi_array of floats

typedef boost::multi_array < float, 3 > array_type3D_f_t;
int dim1 = 2;
int dim2 = 2;
int dim3 = 4;
array_type3D_f_t valueMatrix(boost::extents[dim1][dim2][dim3]);

then for each 3rd dimension I would like to copy a float array into it 
using memcpy
(the final real multi_array will contain approx 21 000 000 elements, and 
thts why I do wish to iterate ).

for (int i = 0; i < dim3; ++i) { // iterate over each 3rd dimension of 
the multi_array
    float *arr = NULL;
    arr = (float*)malloc(sizeof(float) * dim1 * dim2);
    function(&arr) // fills in the array (2D contiguous (dim1 * dim2))
    memcpy(&valueMatrix[something...], arr, sizeof(float) * dim1 * dim2) 
// I want to copy the vector into the multi_array's 3rd dimension
}

then when I want to access an element I simply do

valueMatrix[1][1][1];

what i used to do is

    int level = 0;
   while(it1 != it2){ // it1 and it2 are iterators to a list of records 
holding the data
        float* arr;
        readData(it1, &arr); // read the data into the array
        for (int j = 0; j < dim2; ++j){
            for (int i = 0; i < dim1; ++i){
                valueMatrix[i][j][level] = datavec[ j * dim1+i ];
            }
        }
        ++it1;
        // change level
        ++level;
    }

I would like to replace the nested loops by a memcpy, is this possible?

-- 
Sébastien Fortier