Simple file-format for communicating dense n-dimensional matrices between matlab and C++

fromfile.cpp

#include <algorithm>
#include <numeric>
#include <iostream>
#include <fstream>
#include <vector>
#include "boost/multi_array.hpp"

template<class T, long unsigned int D=2u>
boost::multi_array<T, D> fromfile(std::string f, bool convert_to_c_order=false){
    typedef boost::multi_array<T, D> array_type;
    std::ifstream is(f);
    static_assert(sizeof(int) == 4, "size of int is not four");
    int ndim;
    is.read((char*)(&ndim), sizeof(int));
    assert(D == ndim);
    std::vector<int> v(ndim);
    is.read((char*)(&v[0]), ndim*sizeof(int));

    boost::array<long unsigned int, D> shape;
    std::copy(v.begin(), v.end(), shape.begin());

    boost::multi_array<float, D> vv(shape, boost::fortran_storage_order());
    size_t s = std::accumulate(v.begin(), v.end(), 1, std::multiplies<int>());

    std::fill(shape.begin(), shape.end(), 0);
    is.read((char*)(&vv(shape)), s*sizeof(float));

    if(convert_to_c_order){
        // convert from fortran to C storage order
        boost::multi_array<float, D> vvv(shape);
        vvv = vv;
        //std::cout << (vv.storage_order()==boost::fortran_storage_order()) << "(so)"<<std::endl;;
        //std::cout << (vvv.storage_order()==boost::fortran_storage_order()) << "(so)"<<std::endl;;
        return vvv;
    }
    return vv;
}

int main(){
    auto vv = fromfile<float, 2>("magic5.bin");

    for(int i=0; i<5; i++){
        for(int j=0; j<5; j++){
            std::printf("%02.0f\t", vv[i][j]);
        }
        std::cout << std::endl;
    }
    std::cout << std::endl;
}